Petalia is an anatomic description of cerebral asymmetry where one of the cerebral hemispheres protrudes towards the other hemisphere and thereby causes an impression on the inner surface of the skull 1,2.
The typical configuration in modern humans is the combination of a right frontal lobe petalia and a left occipital lobe petalia i.e the right hemisphere protrudes anteriorly beyond the left, and the left hemisphere extends posteriorly beyond the right. CT and MRI studies show that these petalias are more prominent in right handers. The opposite pattern is seen in left-handedness.
A related term, Yakovlevian counterclockwise torque, is a geometric torsion in hemispheres secondary to their asymmetries, where generally the wider right frontal cortex makes a displacement to left and concomitantly the left occipital pole makes a bending towards the right side, also known as occipital bending. Some studies have shown that petalia and occipital bending have some functional significance and these are more common among patients with psychiatric diseases like major depressive disorder 3, schizophrenia 4, and bipolar affective disorder 5 in comparison to healthy controls. Occipital petalia is also a predictive imaging sign for transverse sinus dominance 3,7.
- 1. Hadziselimović H, Cus M. The appearance of internal structures of the brain in relation to configuration of the human skull. (1966) Acta anatomica. 63 (3): 289-99. Pubmed
- 2. R Shapiro, SJ Galloway, MD Shapiro. Minimal asymmetry of the brain: a normal variant. (2012) American Journal of Roentgenology. 147 (4): 753-6. doi:10.2214/ajr.147.4.753 - Pubmed
- 3. Ezgi Yetim Arsava, Ethem Murat Arsava, Kader Karlı Oguz, Mehmet Akif Topcuoglu. Occipital petalia as a predictive imaging sign for transverse sinus dominance. (2019) Neurological Research. 41 (4): 306-311. doi:10.1080/01616412.2018.1560643 - Pubmed
- 4. Maller JJ, Thomson RH, Rosenfeld JV, Anderson R, Daskalakis ZJ, Fitzgerald PB. Occipital bending in depression. (2014) Brain : a journal of neurology. 137 (Pt 6): 1830-7. doi:10.1093/brain/awu072 - Pubmed
- 5. Maller JJ, Anderson RJ, Thomson RH, Daskalakis ZJ, Rosenfeld JV, Fitzgerald PB. Occipital bending in schizophrenia. (2017) The Australian and New Zealand journal of psychiatry. 51 (1): 32-41. doi:10.1177/0004867416642023 - Pubmed
- 6. Maller JJ, Anderson R, Thomson RH, Rosenfeld JV, Daskalakis ZJ, Fitzgerald PB. Occipital bending (Yakovlevian torque) in bipolar depression. (2015) Psychiatry research. 231 (1): 8-14. doi:10.1016/j.pscychresns.2014.11.008 - Pubmed
- 7. David R. Pettersson, Joel D. McLouth, Benjamin Addicott, Jeffrey M. Pollock, Ramon F. Barajas. The Gibraltar Sign: An Anatomic Landmark for Predicting Transverse Sinus Dominance Laterality on Conventional MRI. (2018) Journal of Neuroimaging. 28 (1): 99. doi:10.1111/jon.12457 - Pubmed