Is Asterion a Reliable Surgical Landmark for the Transverse and Sigmoid Sinus Junction in Indian Skulls?

Background: Asterion is the junction of lambdoid, parietomastoid, and occipitomastoid sutures. In traditional anatomy teaching, it is believed that asterion sits over the transverse-sigmoid sinus junction (TSSJ). It is a significant surgical landmark for the placement of a burr hole in the retrosigmoid approach. Objective: The purpose of this study was to evaluate the asterion's accuracy as a TSSJ-specific external surgical landmark in the Indian population. Materials and Methods: 16 human dried skulls were obtained from the Department of Anatomy, AIIMS, New Delhi. The point of TSSJ was taken between the two lips and just posterior to the entry of the superior petrosal sinus. Asterion internally was localized with the help of a geometrical divider. The x- horizontal/ anterior and y- vertically superior (+)/ inferior (-) distances were measured from asterion (internally) to the TSSJ by a digital vernier caliper. Results: The mean horizontal distance (x) of the left side asterion & TSSJ was 10.3±1.0mm whereas the vertical distance (y) ranged between +2 to -4.3 mm. The mean horizontal distance (x) of the right side asterion & TSSJ was 13.5±1.4mm whereas the vertical distance (y) ranged between +3 to -4.2 mm. Conclusion: Asterion is not a reliable landmark for TSSJ in Indian skulls. The TSSJ with respect to asterion was found on average 10mm and 13.5mm anterior on the left and right side respectively, and mostly inferior (average 4.2mm) in 75% of the skulls. The TSSJ was closer to the asterion on the left side in comparison with the right side. However, further studies with a larger sample size will be needed to evaluate the population-specific relation of asterion with the TSSJ.

Development of myenteric plexus in human foetuses: a quantitative study.

Maturation of neurons of the myenteric plexus (MP) of human fetal sigmoid colon was studied at various weeks of gestation (WG). There is abundant literature on the development of MP in various segments of the gut but there are fewer reports on the development of MP in human sigmoid colon which is a site of various disorders. Sigmoid colonic segments from 12 aborted foetuses aged 14-23WG were processed for NADPH histochemistry. Stereologic evaluation of the neuronal cell profiles, numerical density, number of neurons per ganglion and myenteric fraction was conducted using using imageJ software. According to gestational age, foetuses were assigned into two groups (group 1 [n=7], less than <17WG and group 2 [n=5], more than >17WG). The overall size of neuronal cell profiles in the MP was significantly increased (P<0.05). The numerical density of neurons decreased in group 2 in comparison to group 1, the number of neurons per ganglion and myenteric fraction were increased in group 2 but all these were not statistically significant. This study revealed that the maturational event increases after 17WG and extensive innervations is established at 23WG. During prenatal life there is an increase in the neuronal cell size from 14-23WG signifying maturational process. Such studies are essential for clinicians and surgeons to correlate the normal and pathologic development of the enteric nervous system.