|Year : 2023 | Volume
| Issue : 1 | Page : 102-105
Torus occipitale and occipital bun: Case series of autapomorphic traits
Manaswi Shamsundara1, Nikil Sanaba Paramesh2, Vasudha Kulkarni3
1 Medical Student Phase 3 Part 1 MBBS, Dr. B. R. Ambedkar Medical College, Bengaluru, Karnataka, India
2 Department of Orthopaedics, Dr. B. R. Ambedkar Medical College, Bengaluru, Karnataka, India
3 Department of Anatomy, Akash Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India
|Date of Submission||28-Aug-2022|
|Date of Decision||04-Oct-2022|
|Date of Acceptance||11-Nov-2022|
|Date of Web Publication||02-Feb-2023|
Medical Student Phase 3 Part 1 MBBS, Dr. B. R. Ambedkar Medical College, 48, Karnataka
Source of Support: None, Conflict of Interest: None
Nonmetric characteristics, epigenetic traits, and cranial distinct traits are indicated by tubercles, ossicles, bony protuberances, foramina/notches, and other features on the human skull. For decades, they have piqued the interest of anatomists and anthropologists by supporting and providing evidence for human evolution. Torus occipitale is one such cranial nonmetric variation which is the projection/prominence of inion (midpoint of external occipital protuberance). According to studies, it is caused by the ossification of the ligamentum nuchae's connection to the external occipital protuberance. Yet another nonmetric trait, occipital bun is the posterior projection of the squamous part of the occipital bone below internal occipital protuberance. This case series reports how autapomorphic traits such as torus occipitale and occipital bun are helpful to determine race and the relationship between living taxa and paleontology. These tiny qualitative differences can be used as phenotypic connection markers between groups. We hereby report four types of torus occipitale and cases of occipital bun with their clinical and anthropological relevance.
Keywords: Autapomorphic trait, case series, enthesophytes, occipital bun, torus occipitale
|How to cite this article:|
Shamsundara M, Paramesh NS, Kulkarni V. Torus occipitale and occipital bun: Case series of autapomorphic traits. MRIMS J Health Sci 2023;11:102-5
| Introduction|| |
The occipital bone forms the cranial vault and basicranium. It is widely studied in paleoanthropological investigations as it aids in distinguishing ancient hominin species. Hypoglossal canal, sutural Wormian bones, and torus occipitale are the nonmetric/qualitative characteristics of the occipital bone. These are not quantifiable but aid in the identification of race and fossil kinds. “Elevation of a region between supreme and superior nuchal lines” is torus occipitale. It is located at the intersection of the cranial vault and the basicranium. It has been classified into three types: Type 1 – smooth type, Type 2 – crest type, and Type 3 – spine type. Yet another phylogenetic trait useful in anthropometric studies is occipital bun which refers to the posterior projection of the occipital bone below the nuchal plane.
Evidence from different studies has shown that many tiny autapomorphic traits of the human skeleton can be used as phenotypic connection markers between groups. This case series reports the phylogenetic significance of traits-like torus occipitale and occipital bun in understanding the relationship between living taxa and paleontology.
Occipital spurs are incidental findings in radiograph. These enthesophytes are bony projections at the site of ligament/tendon attachments causing pain in the region of the external occipital protuberance. It gains attention in occipitocervical fixation due to its relation internally to straight sinus and/or confluence of sinuses.
| Case Series|| |
We examined 213 human skulls from the osteology collection for the presence and severity of torus occipitale and occipital bun. We identified three types of tori occipitale and skulls showing occipital bun in 48 of the cases (22.5%).
Case 1: Type 1 – smooth type
We identified 26 (12.2%) cases of Type 1 occipital tori [Figure 1]. This type of occipital torus presents as a smooth elevation at the inion. Type 1 occipital spur was shown to be 67.5% more prevalent in women in prior investigations.
|Figure 1: Image showing skull with torus occipitale Type 1 or smooth type|
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Case 2: Type 2 – crest type
We observed 8 (3.8%) cases of this type [Figure 2]. The bony spur presented as a raised ridge from the surface of the external occipital protuberance. This group is nearly equal in both sexes and is less useful for determining sex.
|Figure 2: Image showing skull with torus occipitale Type 2 or crest type|
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Case 3: Type 3 – spur type
This anatomical skull variant, also known as spine type, is a sex marker in forensic and anthropological investigations, with 63.4% of males and 4.2% of females preponderance. We found 4 (1.9%) cases of this type of occipital spur presenting as spine-like bony projection from external occipital protuberance [Figure 3]. It commonly arises in late adolescence as a result of growth spurts, and when the protuberance expands in size, it causes subperiosteal straining, resulting in discomfort. In certain circumstances, Type 3 manifests as a subcutaneous scalp pseudotumor.
Case 4: The occipital bun (“chignon”)
An occipital bun is the posterior projection/convexity of the occipital squama below the internal occipital protuberance (IOP) and not the thickening of external occipital protuberance as in torus occipitale. It is seen as a concavity in the norma lateralis view just anterior to lambda in parietal bones with or without supralambdoid flattening. We observed 2 (0.9%) cases of occipital bun [Figure 4]. The developmental interactions between the brain, cranial base, neurocranium, and face account for the embryological basis of some morphological variations like occipital bunning. The accelerated growth of basicranium has an impact on the formation of the occipital bun. The presence of a “hemibun” in some Upper Paleolithic Europeans implied Neanderthal – early modern European interbreeding.
| Discussion|| |
We observed the three types of tori occipitale along with occipital bunning in 48 human adult skulls. The description of these cases provides us with evidence of autapomorphic traits as evidence of the racial determination of the South Indian population. The processes that lead to the creation of the occipital torus are caused by appositional bony growth. Occipital configuration is influenced by galea aponeurotica and nuchal muscles such as the semispinalis capitis, trapezius, rectus capitis posterior major and minor, and obliquus capitis superior. Hyperossification is the primary cause of torus occipitalis. It is a phenomenon that occurs in late adolescence due to focal bony exostosis. The lateral extension of the semispinalis capitis, which inserts at the superior nuchal line, creates an enthesis on the occipital bone at the torus. The muscle performs the function of a first-class lever and causes subperiosteal stretching.
Occipital spurs are also called inion hooks or chignon hooks or occipital knobs. They are usually asymptomatic and have incidental findings during radiography. The majority of patients complain of a sensitive bony swelling in the back of their neck that gets worse when they lie down or move their neck. Tenderness results due to subperiosteal stretching as protuberance grows in size in late adolescence. It can be conservatively managed by simple analgesics and soft pillows. In cases of persisting symptoms, surgical recontouring, and smoothening of the protuberance can be done with minimal intracranial risk. Because there is little risk of intracranial penetration and the scarring is minor and disguised by the hair, such surgical procedures are regarded to be relatively safe. Osteoma and skull metastasis form differential diagnoses for this condition. Occipital spur or torus is the characteristic feature of skeletal dysplasia such as atelosteogenesis Type 1. Occipital horn syndrome is a X-linked recessive disorder, with males as carriers presenting with subnormal intelligence and autosomal dysfunction disorders.
Autapomorphic trait evidence
Torus occipitalis is a characteristic of anthropoids and human races (Neanderthal traits). There are two types of character states: ancestral (primitive) and derived. Autapomorphies are derived from character states that are unique. In Asian Erectus, Andrews (1984) hypothesized seven types of autapomorphies. These characteristics include frontal and parietal keelings, thick cranial vault bones, angular torus, occipital torus, the broad separation between inion and endinion, mastoid fissure, and recess between entoglenoid process and tympanic plate. Neanderthals and “Ante-Neanderthals” appear to have autapomorphic torus occipitale. Occipital torus was also found in paleospecies throughout Eurasia and Africa.
Evidence of occipital bunning in earlier studies was obtained from skulls of central European Aurignacian or Gravettian sites such as Mladec, Zlaty Kun, Stetten, Predmostı, Brno, Dolnı Vestonice, and Pavlov. Five grades of occipital bunning have been reported in earlier studies [Figure 5]. Grade 1: no bunning/slight posterior projection of occipital outer table below the IOP; Grade 2 minor bunning, with a slight posterior projection of the internal table of the occipital bone above the IOP and below lambda; Grade 3, moderate bunning, with a significantly more concave internal occipital table above the IOP and below lambda; Grade 4, marked bunning, with a similar degree of internal occipital concavity to Grade 3, but in which the external table is also substantially more developed above the IOP and below lambda; and Grade 5, extreme bunning, with a highly concave internal occipital table above the IOP and below lambda, combined with a thick and highly convex outer table.
There is a need for genome-wide-based analysis studies to determine the genetic basis of torus occipitale and occipital bun as autapomorphic traits of South Indian skulls. A larger sample size is required to classify the occipital bun into subtypes. As a next step, we intend to correlate the presence of these enthesophytes with occipital horn syndrome.
| Conclusion|| |
We found smooth, crest, and spur types of the occipital torus and the occipital bun in 23% of South Indian skulls. Autapomorphic traits-like torus occipitale and occipital bun can be used to determine race and are useful tools for determining the relationship between living taxa and paleontology. In radiographs, they present as incidental findings and present as a differential diagnosis for skeletal dysplasia.
The authors would sincerely thank the principal of DR. B. R. Ambedkar Medical College and Akash Institute of Medical Sciences and Research Centre, Bengaluru, for their keen support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]