Vol.:(0123456789) 1 3 Anatomical Science International https://doi.org/10.1007/s12565-018-0454-x ORIGINAL ARTICLE Prevalence of wormian bones in dried adult human skulls: an osteo‑morphometric study in Nepal Laju Maya Basnet 1  · Sunara Shrestha 1  · Subash Sapkota 2 Received: 13 February 2018 / Accepted: 7 August 2018 © Japanese Association of Anatomists 2018 Abstract The purpose of this study was to determine the incidence of wormian bones (WBs) in diferent head shapes of Nepalese skulls along with their distribution at various sites. This study was conducted on 70 Nepalese skulls obtained from the Department of Anatomy, Nepal Medical College, and the Institute of Medicine from September 2017 to January 2018. The skulls were examined for the presence and topographic distribution of WBs. The occurrence of WBs at various sites was correlated among diferent head shapes. The incidence of skulls showing WBs was 88.57%. The WBs were observed at the lambdoid (61.43%), parietomastoid (41.43%), occipitomastoid (27.14%), pterion (25.71%), asterion (24.29%), lambda (11.43%), sagittal (7.14%) and coronal sutures (4.28%). The dominant head type was dolichocephalic (44.29%) and the least dominant was brachyce- phalic (10%). The maximum number of WBs was shown on brachycephalic (mean 8.86 ± 7.13) then hyperdolichocephalic (mean 8.33 ± 9.15), mesaticephalic (mean 5.10 ± 4.45) and dolichocephalic heads (mean 4.16 ± 5.30). Brachycephalic heads frequently exhibited WBs at the pterion (57.14%) and at diferent sutures: lambdoid (71.42%), parietomastoid (57.14%), sagittal (28.57%) and squamous (14.28%). Hyperdolichocephalic heads displayed more lambda (33.33%) and coronal (8.33%) WBs. Similarly, dolichocephalic and mesaticephalic heads showed WBs at the occipitomastoid (35.48%) and asterion (30%), respectively. Inca bones were only identifed in three dolichocephalic skulls. Neurosurgeons, radiologists and orthopedists should be careful when doing clinical and surgical procedures on diferent head shapes of the Nepalese population. Keywords Brachycephalic · Lambdoid · Skulls · Sutures · Wormian bones Introduction Wormian bones (WBs) are irregularly shaped islands of bones found within the cranial suture and fontanelles. They are derived from additional ossifcation centers and most commonly present in the lambdoid suture and posterior fontanelle (Standring 2016). They were named “wormian bones” after the Danish anatomist, Olaus Worm (Pryles and Khan 1979). An isolated large bone at the lambda is called as an Inca bone or Goethe’s ossicle (Standring 2016). The term “Inca bone” was used because it was commonly observed in the skull of indigenous Incas (South American Indians) (Vishali et al. 2012). These WBs are also present at the pterion as pterion ossicles or epipteric bones (Standring 2016) and at the bregma as the os Kerckring (Vishali et al. 2012). WBs can be observed in healthy individuals as a nor- mal anatomic variant but tend to be smaller and fewer in number (Kaplan et al. 1991). However, a higher incidence of WBs has been observed in patients with certain kinds of congenital disorders (Kaplan et al. 1991) such as osteogen- esis imperfecta, rickets, cleidocranial dysostosis, congenital hypothyroidism, oto-palato-digital syndrome, Down’s syn- drome, and so on, and children with central nervous system abnormalities (Pryles and Khan 1979) such as hydrocepha- lus, microcephaly, macrocephaly, craniosynostosis, cerebral palsy and epilepsy. Knowledge about WBs is essential for radiologists when interpreting skull radiographs as they may be mistaken for fractures in case of head injuries and for neurosurgeons when performing craniotomies (Patel et al. 2015; Murlimanju et al. 2011). * Laju Maya Basnet laju.basnet@gmail.com 1 Department of Anatomy, Nepal Medical College, Kathmandu University, Attarkhel, Gokarneswor Municipality-15, Post Box No. 13344, Kathmandu, Nepal 2 Department of Anatomy, Gandaki Medical College, Kathmandu University, Pokhara, Nepal