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Vol. 28. Num. 1.January - February 2017Pages 1-50
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Vol. 28. Num. 1.January - February 2017Pages 1-50
Review article
DOI: 10.1016/j.neucie.2016.04.001
Cranial trepanation in primitive cultures
La trepanación craneal en las culturas primitivas
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José Manuel González-Darder
Servicio de Neurocirugía, Hospital Clínico Universitario, Valencia, Spain
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Abstract

A review is presented on cranial trepanations performed by primitive cultures. The scientific interest in this topic began after the discovery in 1965 by Ephraim G. Squier of a pre-Columbian trepanated skull, and studied by Paul Broca in Paris. Pseudotrepanation and other types of cranial manipulation are reviewed. The techniques, technology, and instruments for every type of trepanation are well known. There are a surprisingly high percentage of cases showing signs of post-trepanation survival. Indications for trepanation are speculative, perhaps magic. Although trepanation in primitive cultures is widespread around the world, and throughout time, the main fields of interest are the Neolithic Period in Europe, the pre-Columbian period in Andean South America, and some contemporaneous Pacific and African tribes. This particular trepanation procedure has no relationship with modern Neurosurgery, or with trepanations with therapeutic purposes performed since the Greco-Roman period in Europe, and afterwards around the world.

Keywords:
Trepanation
Primitive cultures
Pre-Columbian period
Neolithic period
Kisii tribe
Resumen

En el presente trabajo se revisan las trepanaciones craneales realizadas en el seno de las civilizaciones primitivas. El interés científico por este tema se inicia con el estudio de un cráneo precolombino trepanado encontrado en 1865 por Ephraim G. Squier en Perú y estudiado en París por Paul Broca. Se revisan las seudotrepanaciones y otras formas de manipulación craneal. Las técnicas, la tecnología y los instrumentos para los diferentes procedimientos de trepanación están bien establecidos. Hay un sorprendentemente alto porcentaje de casos con criterios de supervivencia. Más especulativas son las indicaciones, probablemente mágicas. Aunque la trepanación en culturas primitivas se extiende en el tiempo y por todo el mundo, hay 3 focos de mayor relevancia: Neolítico europeo, Sudamérica andina antes de la colonización española y algunas tribus oceánicas o africanas contemporáneas. Esta forma de apertura craneal no tiene ninguna relación con la neurocirugía moderna ni con las trepanaciones con finalidad médica iniciadas en la época grecorromana en Europa.

Palabras clave:
Trepanación
Culturas primitivas
Periodo precolombino
Periodo neolítico
Tribu kisii
Full Text
Introduction

It is often said that trepanation is the oldest recorded surgical procedure. It can also be said that practically all human cultures, in practically all geographic areas and in practically all periods have performed some kind of opening of the skull using different methodologies and with very different objectives, whether known or unknown. In this review, we will refer to the cranial openings or trepanations performed in primitive cultures, including cultures throughout the world and covering different time periods, including the European Neolithic, the pre-Columbian American period until Spanish colonisation in the 15th century, or even contemporary oceanic or African tribal cultures where, leaving aside speculations or theories, it is not truly known why or for what reason they were performed.1–6 In this article, we will review the trepanations in these primitive cultures, highlighting the technical and technological aspects of these practices, without losing sight of the cultural context in which they were performed.

Semantic and conceptual aspects

Trepanations in primitive cultures are also called prehistoric or ancient trepanations.1,2,4,5

Trepanation: Out of the three most significant forms of cranial opening, trepan, trephine and craniotomy, only the first can be found in the dictionary of the Real Academia de la Lengua Española,6 where “trépano” (trepan) is defined as “Med. Instrument used to trepan” [translation], “trepanar” (to trepan) is defined as “Med. To pierce the skull or other bone for the purpose of healing or diagnosis” [translation] and “trepanación” (trepanation) as “Med. Action and effect of trepanning” [translation]. The medical etymological dictionary of the Universidad de Salamanca traces the origin of “trepan” to Greek: “Language of origin: Gr. In Gr. It changed from ‘drill’ to ‘surgical instrument to drill the skull’. In Hippocrates, 5th c. BC, it moved on to mediaeval Latin ‘trepanum’ and it appears in Spanish and mediaeval French.”7 [translation]. Thus, from a semantic and etymological point of view, cranial trepanation should be considered a bone perforation of the skull for the purposes of healing or diagnosis, but the latter cannot be demonstrated in the cranial openings of primitive cultures. On the other hand, the current neurosurgical meaning of “trepan” refers to a small hole made in the skull with a trepan or drill, but it is a fact that very large cranial openings were also made in primitive cultures that cannot be called craniotomies. In spite of all of this and taking this into consideration, in this study we will use the term “trepan” with the broad meaning of cranial opening of variable size and “trepanation” as the technical action and the consequence of trepanning, without any connotation regarding the size, techniques or intentions that led to carrying out such action (Fig. 1).

Fig. 1.
(0.17MB).

(A) Large trepanation of the Andean Paracas culture (700–100 BC). The opening is 11.6cm×9cm, biparietal and affects the superior sagittal sinus. The author states that an anterior bone bridge was preserved to avoid injury to the sinus but that the defects of handling after exhumation fractured it, with only the ends remaining. Colour image at: https://formentinatura.files.wordpress.com/2011/09/la-trepanacic3b3n-y-cirugc3ada-de-crc3a1neo-en-el-antiguo-perc3ba-rc2a9-formentc3ad.pdf. (B) Computed tomography study of a large cranial defect secondary to repeated craniotomies due to recurrent atypical meningioma. (C) Computed tomography study with a 3-D reconstruction of a large cranial defect secondary to two consecutive craniotomies after spontaneous cerebral haemorrhage. The characteristics of modern craniotomy are appreciated, with drill holes, the linear cut between them using a saw and the holes near the cutting edge for lifting the dura mater. Image A taken from Fernández Díaz-Formentí.27

Primitive cultures: In this study, primitive cultures are considered those that meet certain characteristics. The first is that they lack any written documentation, i.e., they are prehistoric. From all that is known of them, and particularly of trepanations, human bones and some marginal archaeological remains have been found which allow us to contextualise the findings. They are extinct or contemporary cultures, developed in confined geographical areas or areas with few exchanges between them. As regards trepanations, as in other aspects of palaeopathology, these cultures had to have performed burial practices on bodies as it was the only way they could preserve skeletal remains for as long as possible.

Pseudotrepanations

Naturally, not all cranial openings found in archaeological remains are trepanations. Because the only information usually available in the case of a drilled skull found at an archaeological site is obtained from the bone remains, the first action is to rule out, from the details of the remains, that it is a pseudotrepanation. In this sense, there are several possibilities.8–11

First, factors that must be analysed include the changes caused in the cranial remains during the process of burial preparation, physical agents used during burial, any necessary manipulation during disinterment and, finally, palaeontological studies and museum preparation. The study of the burial process, decomposition and preservation of the remains buried in the process of fossilisation is a subspecialty of palaeontology named “taphonomy” (from the Greek τ??φοζ, taphos, burial, and νóμοζ, nomos, law), a term introduced in 1940 by the Russian palaeontologist Ivan Efremov. Contamination before burial may be due to many causes: some skulls were drilled post-mortem to obtain bone fragments used as pendants or amulets; others were perforated by impalement to display the heads as trophies or offerings; and finally some skulls may have been drilled in situations of nutritional or ritual cannibalism. There are a number of natural taphonomic agents that can produce holes in the skull, for example, the position, the action of the material surrounding the remains, weather elements, animal bites, particularly rodents, chemical or biological processes that produce erosion, abrasion, corrosion, crushing or bone fracture, or even a lack of part of the remains at the time of burial. In the process of excavation and exhumation of the remains, human taphonomic actions may occur, such as, for example, holes being accidentally produced from spikes or sharp objects, involuntary accidental loss of bone material or during cleaning processes. These deleterious actions produced by man are more likely and serious when transferring remains or in disinterments that are not controlled from an archaeological or palaeontological perspective.

A second cause of pseudotrepanation is the existence of a pre-mortem head injury. There are genetic causes (cranial dysraphism, persistent parietal foramina), tumours (benign or malignant, intracranial or cranial tumours that pierce the skull, whether primitive or metastatic), bone infections (eosinophilic granuloma, tuberculosis or pyogenic infections) or metabolic lesions. One of the most common causes of confusion is traumatic injury with fractures of all kinds secondary to war injuries and even fractures during growth. On this particular topic, when the military weapons used at the time are known or available, it is easy to correlate the number, size and shape of injuries with the weapon in question and rule out pseudotrepanations.

Finally, incorrect interpretations must also be considered. Despite the use of imaging methods for studying remains, including computed tomography and magnetic resonance imaging, there is a tendency for palaeopathologists to interpret the smaller depressions found in the skull as incomplete trepanations or signs of survival, while from a neurosurgical view a large number of these injuries would be considered simple depressed fractures caused by a hard, sharp object. Campillo12 discusses this issue in a review article in the Proceedings of the Seventh National Congress of Palaeopathology, where in some of the papers presented and collected in the same book of proceedings examples can be found of highly debatable interpretation.13

Supra-inial trepanation

Supra-inial trepanation is a particular form of the intentional manipulation of the skull consisting of a simple scraping of the periosteum of the outer table of the skull in the supra-inial region that can exceptionally reach the inner table and result in a hole in the skull. The scraping was done in the midline, above the inion and the superior nuchal line and below the lambda craniometric point. In the mummies in which the soft tissues were preserved, we see that they were performed using a horizontal incision. Apart from bone scraping, the skulls show a new superior nuchal line that is rougher and smoother than the physiological. Several skulls also have deformations caused by bandages and boards. This technique was performed in Peru (especially in the Chancay and Chimu cultures) and Mexico (Chiapas, Yucatán), with an extremely high incidence among the population and is found in skulls of any age and in both sexes. Initially, it was interpreted as the result of cranial deforming bandages or other types, but the sign of incisions in soft tissue found in mummies means that today it is believed that so-called supra-inial trepanation was a prophylactic action to facilitate the use of deforming or other types of bandages, or alternatively it may have had a cultural reason or be from an unknown type of ritual.14

Sincipital T-mutilation

This is another action on the surface of the skull similar to the previous one but less intense. It was described for the first time in France by Manouvrier in 1895 in six skulls from the Neolithic Period, though similar actions have been found in other primitive and developed cultures. Its incidence is very low and appears in brachycephalic skulls, especially children and women. The bone deformity is a T-shaped depression on the midline, with the vertical arm along the sagittal suture and the horizontal arm in both parietals, often close to the lambdoid sutures. It is not known what meaning or justification it had, but this method was used in the 16th17thcenturies in Europe to treat certain mental illnesses. It was performed by cauterising the periosteum and/or bone without any intention to perforate it.4

History

It is now understood that scientific interest in trepanation in primitive peoples has its origins in Ephraim George Squier (1821–1888) and his relationship with Paul Broca (1824–1880).15–17 Squier was an American diplomat and archaeologist who, after completing a mandate from the American government in Peru that started in 1863, spent his free time on his hobby of anthropology. While travelling the country, he found a skull in which he observed and described the obvious signs of a frontal trepanation (Fig. 2). It was a skull found in the region of Cuzco (Peru), from the pre-Columbian period and later dated between the years 1400–1530 AD. Upon his return, in 1865, he submitted the skull for study to the New York Academy of Medicine, which, in its final report, expressed its full scepticism that the trepanation had been done pre-mortem. Disappointed by the report, Squier sent the skull to Paris to be studied by Broca, who was considered at that time to be a global authority on the brain and its pathology, and who had also founded the Society of Anthropology in 1859. Broca concluded in his report that the individual had been trepanated while alive and had survived, also awakening in Broca a personal interest in the study of ancient skulls found in France by himself and others. He did this with the participation of P. Barthélemy Prunières, one of his colleagues. Prunières himself had discovered a perforated skull at the base of a dolmen in 1865 that he initially considered to be a ceremonial vase. In 1839, Morton included drawings of trepanated skulls in a book but considered that the cranial opening was due to an injury.15 Other authors of the period found older references about perforated skulls discovered in Europe, with a finding dated 1685 in Cocherel (France) and another in 1816 in Nogent-les-Vierges (Oise, France), also considered to be the result of injuries.18,19 Thus, Broca and Prunières systematically reviewed the skulls with perforations attributed to injuries and ritual or ceremonial practices and were then considered to be the subject of trepanations, creating the basis of a doctrine on the subject. Major questions regarding the techniques, survival and intentions of trepanation were quickly raised and studied scientifically.1,2,4,5

Fig. 2.
(0.55MB).

Drawing of E.G. Squier from 1877 (A) and photograph (B) that show the skull found by Squier in Peru and studied by P. Broca, with evident signs of frontal trepanation using the polygonal incision technique. Broca ruled that it was a trepanation made while the subject was alive and with survival. The skull was found in the region of Cuzco (Pere), belongs to the pre-Columbian Era and was later dated to the period from 1400 to 1530 AD. From de Arnott et al.1

Survival criteria

A fundamental element in the assessment of trepanated skulls are the individual's signs of survival. These signs cannot demonstrate whether a trepanation had been performed post-mortem or pre-mortem in the case of very short-term survival. In this sense, Lastres and Cabieses20 describe some phases in the bone regeneration process when there is survival:

  • 1.

    When there are no signs of biological reaction of any type in the skull or the physical or mechanical signs of trepanation marks are visible, this means that the death was immediate or that the trepanation was done post-mortem.

  • 2.

    Between one and four weeks after the trepanation, a ring of superficial osteoporosis appears, which is because the hyperemic periosteal reaction mobilises the mineral salts in the area.

  • 3.

    Later, the necrotic bone remains, present along the edge of the bone and wound, disappear. This bone necrosis is the product of the mechanical action of trepanation or a consequence of the devascularisation caused by the removal of the periosteum. If the individual survives long enough, this necrotic bone will disappear as a consequence of the physiological resorption processes. Initially, they are left isolated forming “islands”, giving a moth-eaten appearance to the bone, until they finally disappear altogether (“osteolysis”). A number of processes may alter this biological sequence, such as local infections or cleaning phenomena when obtaining and handling the remains during exhumation or museum conservation processes. In this phase, the edge of the bone is irregular and blurred, and the initial trepanation line is lost.

  • 4.

    The resorption of the islands (“osteolysis“) continues with the “bone remodelling” phase. In this phase, the trepanation edge becomes regular and rounds out, becoming larger than what was initially made. Bone begins to form between the inner table and outer table of the skull. For this, 8 weeks have to have passed.

  • 5.

    Now ossification begins of the scar fibrous matrix, formed due to the precipitation of minerals, by which the bone-shaped radial striations are finally formed and the edges are condensed. The edges of the skull are sealed by an irregular callus between the outer and inner table, so that the cranial hole is rounded, hard and mineralised, with no visualisation of the diploe. A smaller diameter than the initial diameter is maintained and the bevel persists, as the outer table is reabsorbed more intensely than the inner. There may be areas of deep ossification on the dura mater. The lack of osteogenic stimulus (Wolff's Law) prevents the closure of the bone defect. In a few months, the process stabilises. For these latter processes, months of survival are needed.

A simpler classification in three phases has been established by Andrushko and Verano21 and Verano.22 In the first phase, there are no signs of scarring and only the clean borders of the trepanation are recognised. In the second phase, there are osteoclastic changes in the areas surrounding the necrotic bone. Finally, in the late stage of healing, large areas of remodelling and regularising of the trepanation edges are recognised. The problem is the difficulty in recognising these anatomopathological elements in the fossilised biological remains, even with the use of modern imaging techniques including computed tomography scan or magnetic resonance imaging, which can be studied both in the case of trepanation and in the phenomena of bone repair from injuries. However, high survival rates of more than 75% of cases are shown in some studies.8,21 Post-trepanation infection is relatively low, but its presence is in itself a clear sign of survival.

Types and techniques of trepanation in primitive cultures

Since the discovery of pre-Columbian trepanation, there have been several experimental studies to determine the instruments and techniques required to perform it, as there are no archaeological remains or documents to define what specific instruments were used for this purpose. In his book, Lucas-Champonière included several examples of experimental trepanations performed by himself and others at the end of the 19thcentury.4 Thomas Wilson Parry (1866–1945), an English doctor, conducted an extensive practical study by perforating and trepanning skulls using techniques and instruments that supposedly could have been used in the European Neolithic period, which focuses on the use of flint.23 In other experiments, the author drilled with shark teeth, flint points, abrasions with flint stones and cuts with obsidian, showing that each culture used the instruments available in their environment and that each instrument makes a different type and size of hole. Some of these beautiful skulls are on display in the London Science Museum and the photographs can be seen online.24 In general, any new discovery of trepanated skulls in cultures where there were no findings is accompanied by an experimental demonstration of the possibility of performing these trepanations with the materials and tools available in these cultures.25

There are different classifications in relation to the types and techniques of trepanation, although there is some general agreement on the most common methods.1,2,4,5,12–23,25–29 Below, we explain drilling techniques on a carpenter's crown, abrasion, polygonal incision, bevelled incision, circular incision, incision with leverage, percussion and perforation with a cylindrical object.

  • 1.

    Perforation by drilling (“boring”) is the most common technique. It is conducted with a sufficiently hard stone tip that is held with one hand or with a handle, using half-rotation movements which enable the cranial vault to be perforated. This rotation action can be improved by attaching the handle to a rope arc system. If trepanning does not penetrate the endocranium, the resulting hole is conical, while if it passes the inner table, it will be truncoconal. In any event, the hole is always circular, with a larger diameter at the outer table and a smaller one in the inner table. The angle of the hole edges is very large from the outer limit to the inner one. The edge of the cut is clean and no abrasion is seen around the hole, although there may be fleshing grooves or microfractures. The most commonly used materials are microcrystalline rocks such as flint, chert or chalcedony. Other hard materials such as teeth or bones may achieve a similar result (Fig. 3A).

    Fig. 3.
    (0.27MB).

    Diagrams of the most relevant skull perforation techniques. (A) Diagram of trepanation by drilling. The perforation is made using repeated half-rotation movements with a hard, sharp stone. If the inner table is not perforated, a hole with a conical section (left) is created, and if the inner table is perforated, the hole has a troncoconical section (right). The angle of the edges of the hole is very large. (B) Diagram of trepanation by abrasion. The perforation is made using repeated back-and-forth movements in the same direction with a hard, rough stone. The outer table is broadly perforated and the internal table to a more restricted degree, with a bone edge that is slightly slanted and with large exposure of diploe. The opening is usually ovoid due to the curvature of the skull. (C) Diagram of quadrangular incisional trepanation. The incision is made with a hard and sharp knife-shaped stone or rock using a sawing motion, so that the incision has a navicular shape (left). A square fragment is obtained with four incisions using leverage (right). (D) Diagram of incisional trepanation. The incision is made with a hard, sharp instrument, such as obsidian. There is always a larger opening in the outer table than in the inner table, which is usually rounded, with edges that are slightly slanted exposing a large amount of diploe and no abrasion area.

  • 2.

    The “carpenter's crown” perforation is a variant of the above, where several small holes are bored in a circular formation and very close together, in such way that the bone remaining between them breaks with percussion, and a scalloped-edge bone segment is dislodged. It is a very exceptionally observed method and appears in post-mortem trepanations, probably to obtain pendants or charms, for practice or entertainment.

  • 3.

    The abrasion technique (sanding or scraping) requires a grainy or vitreous stone, for example, a core of flint, chert or chalcedony, from which flakes have been removed to create edges. The stone is used to file down the surface of the cranial vault which, as it is rounded, allows a hole to form which in this case is ellipsoid. It is usually surrounded by an abrasion area that is longer depending on how small the curvature of the skull is. In this case, the perforation is of much smaller dimensions in the inner table than in the outer table and the edges of the hole have a small angle. It is the oldest trepanation technique and has the highest survival rate, although the area of abrasion may be confused with an area of bone regeneration (Fig. 3B).

  • 4.

    The polygon incision (“polygonal cutting”) technique consists of making crosswise incisions forming a polygon. The polygonal technique is performed with a flint or obsidian stone carved into the shape of a knife and consists of making one or more incisions using a sawing motion that, given the curvature of the cranial vault, have a spindle-shaped morphology. When the cranial vault is not fully perforated, Latin American authors have compared its shape to a Native American canoe. When several overlapping incisions are made, the trepanation is polygonal, most commonly quadrangular. This method was rarely used in Europe, although it was a very common technique in South America. Occasionally, there is only one spindle-shaped groove or multiple grooves that do not complete a polygonal resection. When there is a complete polygonal figure, it is normally a square. In the polygonal incision, a bone plate is obtained, usually by “leverage” in one of the grooves, which could lead to obtaining incomplete skull fragments or additional skull fractures (Fig. 3C).

  • 5.

    For the bevelled incision technique, a hard and sharp stone is needed. A section of the cranial vault's surface is bevelled towards the centre of the perforation towards the inner table, forming a roughly circular or ellipsoidal central hole surrounded by an area of long bevelled abrasion and very little slanting. In this case, the perforation has dimensions that are much smaller in the inner table that in the outer table. A “slice” of bone is removed (“rondelle”). Obsidian stones were used to conduct this technique (Fig. 3D).

  • 6.

    Circular incisions (“circular grooving”) involve carving a groove in a circumference and prying up a bone disc. To do this, a ringed groove is made with a sharp tip, going over the initial groove several times, which becomes deeper and deeper, until it reaches the inner table. At this time, leverage may be used to pry up a bone fragment or slice that is more or less oval or circular. The circular abrasion and incision methods can be difficult to distinguish in a trepanated skull, particularly in the case of trepanations with survival, but in the latter, a slice of bone is obtained in the end and the edges are more angled.

  • 7.

    Incision with leverage is an uncommon method. One or two longitudinal incisions are made and the skull is fractured using leverage.

  • 8.

    Percussion is done with a hard cylindrical object of wood, bone or stone that is struck with a heavy object that acts as a hammer.

  • 9.

    Perforation with a hollow cylindrical object is done by rotating a hard hollow wooden or bone object and using abrasive sand. A cylindrical hole is obtained with vertical edges and a cylindrical slice of bone.

The materials used in the ancient primitive cultures for trepanation were eminently lithic, especially flint and obsidian. Flint, as well as chert and chalcedony, are rocks that are very rich in silica with a microcrystalline structure that gives them great hardness (flint: 7 on the Mohs scale). All of them are very abundant rocks and the difference between them is geological, although for practical purposes all are equally useful for trepanations by drilling or abrasion and even incision. Obsidian is an igneous rock belonging to the group of silicates which is also very hard (5–6 on the Mohs scale), but when it breaks apart it provides relatively hard and very sharp edges, which makes it especially useful in trepanation by drilling or incision. Some later primitive cultures had access to metallurgical materials, although the available alloys were very poor quality for trepanation. However, they could be useful for soft tissue. In pre-Columbian Peru, the most classic instrument was the “tumi”, made of an Incan bronze alloy or “champi”,28 and other later European civilizations also used bronze knives.25 Contemporary primitive cultures use metal and even surgical instruments for trepanation.1

What is even more speculative is how the soft tissue was handled at opening and closure and what measures were used for analgesia, haemostasis and infection prevention. In some pre-Columbian mummies, there are straight line or star-shaped incisions on the soft tissue. Closure could have been done by tying the hair, suturing with a needle and thread, applying ant heads or a compression bandage. It is speculated that hallucinogenic drugs or alcoholic beverages would have been used as painkillers. The use of antiseptic methods is also unclear, though the resistance of primitive peoples to wound infections is well-known and, in fact, there are few trepanated skulls with signs of survival and associated signs of bone infection.

As an interesting neurosurgery curiosity, there are two descriptions in the literature of in vivo trepanations performed by neurosurgeons on patients in the 20thcentury, using sterilised pre-Incan trepanation instruments, demonstrating that it is possible to successfully perform craniotomies using these instruments. These are summarised by Marino and Gonzales-Portillo.28

In 1944, two Peruvian neurosurgeons performed a trepanation using instruments from the Archaeological Museum of Cuzco on a 22-year-old male who presented a head injury after a tree fell on his head. They made an incision on the scalp using a “tumi”, which was also used to elevate the periosteum; they used a sterilised Inca obsidian chisel to open the bone and performed an oval craniotomy of 6cm×3cm. The edges of the wound were sutured with a “champi” Inca bronze needle. The procedure lasted 1h. The patient died seven days later from bronchopneumonia.

In 1953, another two Peruvian neurosurgeons, Graña and Rocca, performed an experimental trepanation with an Incan “tumi” on a cadaver. They made a 3cm incision in the scalp, and the bone was perforated with an obsidian knife from the National Museum of Anthropology and Archaeology in Lima. They found that obsidian knives broke when they made circular motions to perforate the bone and that the best drilling technique with obsidian tools was to make sawing motions. In this way, they created a square craniotomy. Later, they performed an in vivo trepanation with the same instruments in 1953 on a patient with head trauma followed by hemiplegia and aphasia. After anaesthetising and intubating him, they performed a trepanation with sterilised Incan instruments. The incision on the scalp was made with a “tumi” and the craniectomy, oval in shape, was performed using a flint chisel. After exposing and opening the meninges, a subdural haematoma was drained.

Historical and geographical setting of trepanations in primitive cultures

As previously stated, the practice of trepanation is extended practically throughout the world and over all periods of time, though predominantly in the European Neolithic and American pre-Columbian eras. An important aspect on this point is that many civilizations throughout history did not bury their bodies, so it is not possible to find trepanated skulls in cultures that left corpses in the open for animals or underwent cremation. In these cases, due to the absence of documented evidence to the contrary, it cannot be confirmed or denied that they performed trepanation.

  • 1.

    In Europe, the Neolithic Period is considered to have started at about 5000 BC, coinciding in Europe with the appearance of agriculture, and ends with the introduction of bronze metallurgy at around 2000 BC. Trepanations were performed throughout Europe in this vast period and at the start of the Bronze Age.1,30 The country with the highest number of findings is probably France, accumulated in the department of Lozere and in the region of Seine-Oise-Marne. Interest in this type of findings was important in the early years following the initial proposals of Paul Broca, especially in the surgical environment. Consequentially, it is covered extensively in the French treatises of the period on neurological and cranial surgery. As examples, Chipault dedicated several pages of his book Chirurgie opëratoire du système nerveux, published in 1894, to Perforations crâniennes préhistoriques.18 Terrier and Péraire did the same in their book L’opération du trepan, published in 1895.19 In the Iberian Peninsula, a total of 100 cases of prehistoric trepanation have been documented up to 2007, predominantly in the coastal areas, especially in the Mediterranean.2 The techniques are varied, but the incision technique was uncommon. They were performed pre-mortem, clearly for ritual reasons, probably as painful initiation techniques and only exceptionally due to injuries. Several are clearly post-mortem. In the Mediterranean area, there are also prehistoric trepanations in Italy, with 36 documented cases up to 2015 using abrasion and drilling techniques, with rare cases of incision as in the Iberian Peninsula. The skulls are of adults trepanated in the frontal and parietal regions, with a high frequency of bone signs indicating survival.11 Discoveries of trepanations throughout Europe continue to be published on a regular basis at Neolithic sites, such as in Germany,30 and from the Bronze Age, as in Greece,31 and even in the Pazyryk culture of the 6thcentury BC-2ndcentury BC-2ndcentury AD of the Altai Mountains in Russia.25 As previously stated, in Spain there is a significant number of trepanated remains and abundant literature on the subject.2,3,12

  • 2.

    In pre-Columbian American cultures, the number and frequency of trepanations overwhelmingly surpass those of the European Neolithic period. At this point, several areas should be considered, specifically the Andean area, Mesoamerica and North America.

    • a.

      The first documented trepanation refers to a skull found on the southern coast of Peru dating from the year 400 AD. In the Andean areas of Peru and Bolivia, there is a first period with trepanations that is part of the pre-Incan period prior to the 10thcentury when Incan rule starts.1,21,26–28,32 The term Pre-Incan indicates the cultural and historic reality of a specific territory before its annexation by the Incas and this includes the Chavin, Paracas, Nazca, Mochica, Huari, Tiahuanaco, Chimú and Huanca cultures. In these areas, and for these cultures, there was a large number of cases excavated without guarantees at the end of the 19thcentury and start of the 20thcentury, but the number of skulls is massive. Some 15,000 skulls from the pre-Columbian Andean highlands have been catalogued, and more than 2000 of these skulls were trepanated. About 5–6% of the mummies found in Peru had been trepanated “in vivo”. Each culture prefers to use one technique or another.21,26–28,32 As an additional item of interest, there are findings that would correspond with the description of the first cranioplasties in history. Thus, there is a skull with a frontal skull defect on the medial line located on the superior sagittal sinus and repaired with a nutshell. Obvious signs of bone regeneration confirm the survival of the individual and that the cranioplasty was performed pre-mortem.33,34 Another skull found in Cerro Colorado of Paracas shows a small left frontal trepanation, repaired with gold foil which widely covered the frontal region.34,35 The most likely indications for trepanations would be injuries and ritual acts.

    • b.

      In Incan Peru, whose capital was Cuzco, trepanations were performed until Spanish colonisation in 1532, and probably for a period of time afterwards, though there is no record of this in the Spanish documents of the time. The incidence of trepanated skulls is extraordinarily high, though variable depending on the site: in Urubamba, 17% of 341 cases were trepanated; in Calca, 20% of 55 cases were trepanated; and, in Cuzco 16.1% were trepanated. On the other hand, in Machu Picchu there are no trepanated skulls, which has been justified by the fact that the inhabitants belonged to the nobility. Andrushko and Verano21 exhaustively studied a collection of 709 skulls from Cuzco and the surrounding areas after the 10th century which included 411 that were in good condition and were from subjects over 5 years of age, showing that 16.1% had been trepanated. The techniques were highly standardised in Incan Peru, with circular incisions and abrasions in all cases, except for one case with a polygonal incision technique. There are between one and seven perforations per skull, with a mean opening of 5.5cm2, and trepanations located in the parietal (72%), frontal or occipital bone on the left (27.5%), centre (60.6%) and right (12.7%) sides, on sutures in 44% and in areas of muscle insertion in 11%. The subjects were mostly young adults and adolescents, not children, with a male/female ratio of 1.84. There is evidence of an underlying pathology in several cases, especially injury (44%) and, to a lesser extent, mastoiditis (3%). The bone signs of survival are very common (83%), with only 4.5% of post-trepanation bone infections.

    • c.

      Trepanated skulls have also been excavated in Central America, especially in Yucatan and Monte Albán in Oaxaca Valley, Mexico. About 25 cases have been found corresponding to the so-called classic period (250–800 AD). Most trepanations were performed by abrasion and drilling, but there are seven skulls with drill holes of about 11mm in diameter made with a reed or bone and abrasive sand, and usually multiple in presentation (up to five in one case). The proposed indications include rituals, headache and headache due to cranial remodelling.35,36

    • d.

      Some trepanated skulls have also been found in North America. By 1990, 19 cases had been described (11 in Canada and 8 in the USA), all from the pre-Columbian period and performed with an abrasion technique in the parietal (9 cases), frontal (3 cases) and occipital (3 cases) regions. One skull had two trepanations, and the average opening area was 3cm2. None of the cases showed fractures, and bone signs of survival were the norm (90% of cases).37,38

  • 3.

    In contemporary primitive cultures, there is documented and even iconographic information of trepanation being performed in very recent times within primitive Berber cultures in northern Africa, on the islands of Polynesia1,4,19,39 and black tribes in central Africa.1,40–42 Thus, in the “Kisii” tribe in Kenya, trepanations are occasionally performed using modern surgical instruments for the incision and closure of the soft tissue and perforation of the skull. The act is indicated and performed by the tribe's “shaman”, or medicine man. As in all ethnic groups of Kenya, the medicine man (“ubanyamorigo”) has a very privileged position in the tribe. One of the practices still used is the resection of part of the spine or skull in cases of back pain or brain problems. One of these procedures was documented in pictures by a journalist, and a full photographic sequence is available online.43 Even though it was not published until 1994, the article that is presented was written in 1977 and was photographed by Michael D. Mueller, a member of the New York Explorers Club.42 The patient was a young woman with a five-year history of headaches and dizziness after a fall and head injury. She moved slowly and was unable to show emotion. The procedure was performed by the “omobari omotwe” (head surgeon) and the photographic article sequentially follows the entire surgery and the patient's postoperative condition. Another procedure of this type performed by the “kisii” is available on YouTube.44

Discussion

Scientific interest regarding ancient skulls exhumed with cranial perforations began with the recognition by Paul Broca that the Inca skull sent by Squier for study had undergone a trepanation in life that the individual had survived.15–17 An initial phase of scepticism had to be overcome, as it was considered almost impossible that primitive peoples could successfully perform surgical procedures that medicine in the second half of the 19th century rarely performed, with outcomes that were not encouraging and, even worse, were much more limited in terms of the size of the cranial opening or areas addressed and clearly less sophisticated in all aspects considered. Something similar happened with the Palaeolithic cave paintings of Altamira, discovered in 1880, which for more than a couple of decades were declared as fraud by European specialists of the time as they believed that the paintings had too much artistic quality to have been painted by Palaeolithic men. Immediately afterwards, and thanks to the impetus of Paul Broca himself, previous findings of perforated skulls were reviewed, many of which were considered trepanated, and new specimens were provided. Soon the scientific discussion focused on the technical aspects, survival, and the reasons why they were performed.

The map of trepanated skull findings spreads across the world, but they are particularly prevalent in Europe and America. They have also been found in all historical periods, with the highest incidence in Europe in the Neolithic Era and the pre-Columbian Era in America.1,2,4,5,8–11,14–34,36–42 This practice has been called “prehistoric trepanation” or “ancient trepanation”, but even though the term trepanation is preferable to craniotomy, we consider it is more useful to refer to “primitive cultures”, as we have done here, since it allows us to include trepanations that are performed in a certain cultural setting, as defined above, excluding geographical or chronological factors.

Currently, there is little doubt about the materials and methodologies that were used for these trepanations, and multiple well-documented experimental studies have proven that it is possible to perform them with lithic materials. We have also reviewed various trepanation techniques, which are well described, and which have also been reproduced in several experimental studies.1,2,4,5,11,21,22,25–28 Furthermore, there have been two published craniotomies performed successfully in Peru by neurosurgeons using the materials and techniques used in the pre-Columbian period, which show that they can be performed by experienced people.28

Taking into account the geographical isolation and varying time periods among the different cultures that performed trepanations, it can be asserted that the technical materials and solutions were generated autonomously, without learning phenomena among them. A crucial aspect is the stone material available in the geographical environment of the culture that performed the trepanation, or one that could have easily been available through trading. Thus, microcrystalline rocks like flint, chert or chalcedony are particularly useful for abrasion or drilling techniques, and they were used in Europe where they are abundant. However, thousands of years later in America, obsidian was used, which allowed incision type techniques to be employed. Other cultures used shark teeth and other accessible materials.23,39 More modern or contemporary cultures include metallic or even modern surgical instruments in the materials.1,4,40–42 So, if geographical isolation and varying time periods of the main areas of trepanation made it virtually impossible to consider shared knowledge or learning among these cultures, the preference for one or more forms of trepanation in each culture indicates that, although they independently arrived at the same instrumental solutions, where a crucial aspect was the type of drilling equipment available, the general methodological aspects are very similar. The alternative to this hypothesis is the theory of “diffusionism”, which has been discussed and rejected, at least in regard to the European Neolithic cultures and pre-Columbian American periods.45

One factor that has led to greater speculation is the question of survival. It is impossible to differentiate between a post-mortem trepanation from another performed on a living subject but with very short survival. Survival is based on demonstrating signs of bone resorption and regeneration in the remains. The phases of bone resorption and repair are described from an anatomopathological point of view and translate into longer or shorter periods of survival.20–22 However, these changes are really difficult to put into evidence in the skeletal remains by direct observation or even with the use of modern imaging techniques, given the state of these pieces from taphonomic processes.11,25,31 From a neurosurgical standpoint, when we examine images from studies where long-term survival is claimed, assertions that have been made are often too forceful. Thus, any bone filling of the bottom of a cranial bone hole, regardless of size, is almost automatically interpreted as a sign of long survival. However, it is exceptional in modern neurosurgery to find this ossification after bone decompressions or decompressive craniotomies of any size, even after years of evolution (Fig. 4). In fact, these ossifications at the sites of cranial defects are only observable for trauma with untreated comminuted or depressed fractures or those that are treated where sufficient bone matrix has been left. Although the dura mater has osteogenic capacity, the lack of osteogenic stimulus due to the absence of compressive forces or distraction from Wolf's law makes a large osteogenic response unlikely. In children, the problem is different, as can be seen in the surgical treatment of craniosynostosis, where the cranial windows usually ossify. These considerations are not an obstacle to recognising that a significant percentage of trepanated individuals survived for a long time.8,10,21,26,27 The same is true of many of those who had depressed or fragmented skull fractures secondary to severe direct trauma, usually from acts of war, whether or not they were trepanated.

Fig. 4.
(0.17MB).

Cranial tomography studies with bone window in three patients undergoing neurosurgical craniotomy with high-speed motor saw, no bone replacement or complications and different follow-up times. (A) Study conducted two weeks after the craniotomy, where the bone edge of the cut with the outer table, diploe and inner table are clearly visible. (B) Study conducted three years after the craniotomy. The cutting edge of the craniotomy is seen to be rounded. (C) Study conducted more than 10 years after the craniotomy. The cutting edge is rounded and with a newly formed edging of compact bone. There are no signs of calcification or ossification on the plane of the dura mater within the bone defect.

The most intractable problem is the reason that led to performing a trepanation. In this sense, there are different positions, but generally all are speculative and are based on contextualising the supposed indication of trepanation within known or suspected cultural elements of the specific civilization where it was performed. In the absence of documentary evidence, the main reasons invoked are ritual (particularly religious, magical or initiation rites), medical (headache, psychiatric disorders, epilepsy) and surgical (treating wounds, fractures or cranial or intracranial injuries).

If it is accepted that trepanations were conducted for medical-surgical reasons, the truth is that pathology is only found in trepanated skulls in the presence of trauma or mastoiditis, which offer external physical signs. In the other cases, it would be very risky to assume the coexistence of medical knowledge for a clinical and topographic neurological diagnosis, which in modern medicine was only reached at the end of the 19th century. Moreover, even assuming the above, i.e., that there was pathology in all cases, the frequency of trepanations in many cultures far exceeds the current rate in the Western world. Furthermore, several trepanations are clearly post mortem. If Inca trepanations had been a routine example of medical and surgical treatment in the context of highly sophisticated medicine, it would have drawn the attention of the Spanish, and there are no references about this practice.

As indicated above, the relationship between trepanation and recognisable cranial or intracranial pathology in the bone remains is anecdotal. Even though at present it is exceptional to make a diagnosis of cranial or intracranial pathology from data obtained from their direct or indirect bone impact, thanks to early diagnosis and the use of modern imaging techniques, it is true that many evolved pathological processes are capable of producing gross bone changes in the skull. These changes are those that provided the diagnosis of cranial and intracranial lesions through direct and indirect radiological signs in simple radiologic studies of the skull until well into the 20thcentury.46 These signs, which presumably could be recognised with some ease in trepanated skulls, are in fact not found if we exclude fractures or mastoiditis.

As medical-surgical indications are reasonably excluded, sociocultural reasons are proposed. The differences of any social or cultural aspect between civilizations can in fact be extreme. The sociocultural environment of the European Neolithic Period was clearly different from that of the Incan Empire, which was much more complex and developed. Therefore, it is difficult to think that in both cultural environments the same solution was proposed for the same problem using the same arguments. In light of these attempts, there are overall and more practical proposals, such as that of Domingo Campillo, a leading Spanish researcher of Palaeopathology and a neurosurgeon, who postulates that all trepanations could be magical.2,8 Magic is the method primitive cultures used to anticipate and solve all types of problems. Magic acted through rites performed by a “shaman” or the tribe's medicine man. One of these rites would be trepanation, without being able to infer more about the actual justification of its practice in a specific case. This would explain the weak relationship of trepanation with pathology, the variability of its practice, the high frequency of trepanation in some cultures and the surprisingly high survival rate of trepanated individuals.

It is important to categorically separate this type of trepanation from craniotomies that we perform in the field of modern neurosurgery,47 a relationship that is usually made repeatedly in the media, specific settings and publications of science and pseudoscience. Interestingly, this conceptual pollution has been allowed in prestigious neurosurgical journals. Neurosurgery published an article entitled “Peruvian Neurosurgeons of the Pre-Conquest”28 and in World Neurosurgery it is stated that, “the neurosurgical profession must be one of the oldest in the world”.31 However, these trepanations are unrelated to those carried out before modern neurosurgery, where the trail of cranial techniques can be followed retrospectively to the Hippocratic texts dating back about 400 years BC. The surgeons who performed trepanations during this time also cannot be called neurosurgeons and, interestingly, no one has called them that. The Hippocratic text “Head Trauma” describes the types of traumatic cranial lesion (contusion without fracture; contusion with linear fracture; depressed fracture; perforation of the skull with indentation; remote lesion), types of treatment (incision and wound examination; trepanation, which should be avoided in depressed fractures and over sutures and should not penetrate the dura mater), the technique of trepanation (removing bone up to the inner table, without reaching the dura mater) and the required instruments (drill and serrated drill or “modiolus”; probe; scraper).1 In these cases, the trepanation was always clearly therapeutic in its intent, regardless of the scientific paradigms on which it was based, and since there is no cultural or chronological relationship between European Neolithic civilizations and the Greco-Roman world, much less between these and pre-Columbian civilizations, there is no argument that can bring these various practices together.

Conflicts of interest

The authors declare that there are no conflicts of interest.

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Please cite this article as: González-Darder JM. La trepanación craneal en las culturas primitivas. Neurocirugía. 2017;28:28–40.

Copyright © 2016. Sociedad Española de Neurocirugía
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