Morphometric Analysis of Accessory Sutural Bones Association With Parietal Emissary Foramina

Background: The sutural bones and fontanelle of the skull display unique morphological characters. Sutural bones are also called supernumerary bones or ossicles or Wormian bones (WB). These are irregular and develop from the independent ossification centers present along the cranial sutures. They appear on periosteal and endosteal surfaces of the skull with variations in size, number, shape, and location. In the present study, we aimed to determine the morphological characteristics of sutural bones and association with parietal emissary foramina. Methods: The present study was done on 128 dry human skulls by a convenient sampling method. The skulls were collected from the Department of Anatomy and considerable characteristic features of Inca and Wormian bones like shape, number, size and location were recorded. Included abnormal parietal emissary foramen associated with the Wormian and Inca bone respectively. Results: Out of 128 dry skulls, the Wormian bones were seen in 13.2 % of skulls and Inca bones in 5.4 % of skulls. Incorporation of Wormian bones in the lambdoid suture was noted in 12.5 %, in the sagittal suture 0.7 % skulls respectively. The Wormian bones were found frequently on the left side (n=12) as compared to the right side (n=5). The morphometry of the accessory bones showed quadrilateral as the most common shape (n=9, 37.5 %) followed by triangular (n=4, 16.6 %). Radiological examination of all 24 skulls with accessory bones showed a zigzag pattern of accessory suture lines. The prevalence of abnormal parietal emissary foramen (bilateral and unilateral absence associated with the Wormian bone were noted in 23.5%. The prevalence of abnormal parietal emissary foramen (unilateral absence and foramen on the sagittal suture) associated with the Inca bone were noted in 71.4%.  Conclusions: The presence of Wormian and Inca bones can be easily confused with fractures of the related bony regions. The surgeons need to be aware of this fact in order to make a proper and accurate diagnosis. The knowledge regarding these bones is highly beneficial to the clinician, radiologist, and neurosurgeon.