Smt. NHL Municipal Medical College, Ahmedabad

Research article Sexing the human skull using the mastoid process. Swati Shah*,Pratik Patel** *Asst. Professor, Department of Anatomy,**Professor & head,Forensic medicine

Smt. NHL Municipal Medical College, Ahmedabad

ABSTRACT Sex determination of human or human skeletal remains is considered an initial step in its identification. In cases of fragmented or mutilated body, it is difficult to identify the body. This skillful process is carried out by forensic and anatomy experts. In cases where intact skull is not found, mastoid play a vital role in sex determination as it is the most dimorphic bone of skull. The mastoid region, a fragmentary piece of skull is ideal for sex determination as it is resistant to damage due to its anatomical position at the base of skull and its toughness. The skull measurements vary significantly in different ethnic groups of the world and number of research/studies are too few for Indian population. In present study, 100 adult human skulls of Gujarat population were studied to determine accuracy of mastoid process in sex determination. A quantitative blind study of the dimensions of the sides of the mastoid triangle was carried out. Results show significant craniometric difference between male and female mastoid triangles. KEY WORDS Asterion, craniometrical points, heron’s formula, mastoid triangle, mastoid, porion, sex determination. INTRODUCTION Identify means “determination of the individuality”. In number of civil and criminal matters identification of the individual, either living or dead, is required. The anatomical and medical features are the two major aspects to establish the identity. The establishment of identity is required from fresh intact corpses, decomposed corpses, mutilated and dismembered corpses or skeletalised material.1 Sex determination of human or human skeletal remains is considered vital step in identification and is crucial for further analysis. When performing a forensic anthropological analysis for human identity, sex estimation of the individual is

one of the first and most important steps. In living, identification is possible with absolute fixation of the individuality but in case of advanced decomposed, mutilated or skeletalised body it is difficult to establish the identity of the dead body either partially or completely. In such circumstances the identification of human skeletal remains a critical issue. In present forensic scenario, dismemberment or mutilation of body has become the frequent method to conceal the identity of victim. In such instances the pelvis is considered the best bone to determine the sex of an individual2. When the pelvis is unavailable the skull is also widely considered the best indicator of sex. Krogman3 states that skull is the most dimorphic and easily sexed portion of skeleton after pelvis, providing up to 92% reliability. Bass4 states that the skull probably is the second best area of the skeleton to use for determining sex. Bass4, Byers5 and Pickering and Bachman6 presented the idea that skull is the second best choice to estimate the sex of the dead body. With intact skull descriptive features are traditionally considered rather than dimensions [size and proportions] to estimate the sex of the corpse. However in fragmented skull bone both metrical and morphological characteristics may be helpful to determine the sex3. In the skull, the mastoid bone is robust and tough making it resistant to physical damage. The mastoid region is favorable for sex determination for two reasons, the compact structure of the petrous portion and its protected position at the base of the skull. So it is commonly found remained intact in skeletons of very old age. Even though skull is fragmented, the mastoid stays intact. From the size of mastoid sex can be presumed i.e. a larger mastoid suggests male sex and a smaller mastoid suggests female sex. As it’s the subjective and comparative criteria, it can not be relied upon. Henceforth individual parts of the skull like mastoid have been analyzed by few researchers for sex determination. Mathematical dimensions of various parts of mastoid are used by craniometric techniques to identify the

75 NHL Journal of Medical Sciences/July 2013/Vol.2/Issue 2

sex in fragmented skull bone. Nagaoka T method is employed by some experts using two parameters on both sides of skull i.e. height and width of the mastoid7. This method has its own merits and significance. Paiva & Segre (2003) after studying a sample of 60 skulls introduced an easy technique for sex determination starting from the temporal bone. The technique is based on the triangular area calculation obtained between the points porion, mastoidale and asterion, measured from xerographic copy of skulls8. This technique has significant degree of predictability with a small observational error. Multiple measurements instead of single measurement of mastoid have increased its significant value. AIMS AND OBJECTIVES The objective of this study is to provide a new method for determination of sex of fragmentary human skeletal remains of natives of Gujarat state, India, using the three craniometric points of mastoid process i.e. the mastoidale, porion and asterion.

MATERIAL AND METHOD 100 dry skulls of known sex, 50 male and 50 female, from the department museum of anatomy of various medical colleges from Gujarat were analyzed for the present study after taking approval of Institutional Review Board of Smt NHL Municipal Medical College and written permission from the concerned department/ institute. Adult skulls of mature individuals, 18 or more years old, without destruction of the mastoid bone in the region of the craniometrical points, were chosen for the study. The skulls that present evidence of injury/fracture or deformity were excluded from this study. All the skulls were confirmed of the individual of native of Gujarat state, India from the concerned department record. Three points on the mastoid portion on either side, porion [upper most lateral point of external acoustic meatus pore], Mastoidale [the most inferior point of mastoid process], Asterion [the meeting point of three posterior skull sutures i.e. lambdoid, occipitomastoid and parietomastoid] were selected as area of our study. These craniometrical points were marked by a single investigator. A triangle was prepared/drawn using these three points on skull bone

on both sides. Porion, asterion and mastoidale were referred as Po, As and Ma respectively. Measurements of the dimensions of the sides of the mastoid triangle were carried out using vernier caliper. Any of these three points if found damaged, the skull was excluded from the study. The area (mm2) of the demarcated triangle for each side of the skull (right (R) and left (L) sides) was determined by Heron’s formula9 and the total value (T) of these measures of both sides was calculated as per method described by De Paiva and Segre8, Helmuth10, Demoulin11. DATA MANAGEMENT AND ANALYSIS Using appropriate analytical software, the data was analyzed. The descriptive statistics of the lineal dimensions and the mastoid triangle area were calculated. DISCUSSION & CONCLUSION The studies for sex determination of the bones are based on the dimorphism that is present in the majority of human bones. The present study was carried out using method applied by other researchers, based on craniometric dimensions of mastoid part of the skull. Total 100 dry skulls were measured. Out of these, 49 were male skulls and 51 were female skulls. The mean of Heron’s triangle was as follows. Table 1: Male and female right and left side measurements GROUP Male Right Male Left Female Right Female Left

NO. 49 49 51 51

MEAN 663.66 662.54 595.92 589.29

S.D. 68.77 64.031 96.704 81.963

Table no. 1 shows various values of male right, male left, female right and female left side in the study population. Mean values of male skulls were found significantly high on both sides in comparison to that of female sex.


Means of the mastoid dimensions and mastoid triangular area of skulls (whole skull or fragments) provide an accurate method for determining sex.


Table 2: Comparison: male and female right and left side using Student t-test. P -value

’t’Value

Degre e of freedo m

Level of Significance

Male Right side Vs Female Right side

4.023

98