Case Report Atypical Intracranial Epidermoid Cysts: Rare Anomalies with Unique Radiological Features Eric K. C. Law, 1 Ryan K. L. Lee, 1 Alex W. H. Ng, 1 Deyond Y. W. Siu, 1,2 and Ho-Keung Ng 3 1 Department of Imaging & Interventional Radiology, Prince of Wales Hospital, e Chinese University of Hong Kong, Shatin, Hong Kong 2 Department of Radiology, Kwong Wah Hospital, Kowloon, Hong Kong 3 Department of Anatomical & Cellular Pathology, Prince of Wales Hospital, e Chinese University of Hong Kong, Shatin, Hong Kong Correspondence should be addressed to Eric K. C. Law; ekclaw@gmail.com Received 12 August 2014; Accepted 26 December 2014 Academic Editor: Yoshito Tsushima Copyright © 2015 Eric K. C. Law et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Epidermoid cysts are benign slow growing extra-axial tumours that insinuate between brain structures, while their occurrences in intra-axial or intradiploic locations are exceptionally rare. We present the clinical, imaging, and pathological indings in two patients with atypical epidermoid cysts. CT and MRI indings for the irst case revealed an intraparenchymal epidermoid cyst that demonstrated no restricted difusion. he second case demonstrated an aggressive epidermoid cyst that invaded into the intradiploic spaces, transverse sinus, and the calvarium. he timing of ectodermal tissue sequestration during fetal development may account for the occurrence of atypical epidermoid cysts. 1. Introduction Epidermoid cysts are benign, slow growing extra-axial tumours that account for ∼1% of all intracranial tumours [1]. Embryologically, they are derived from ectodermal inclu- sions during neural tube closure from the third to the ith weeks of embryogenesis [1, 2]. hey frequently occur at the cerebellopontine angles and parasellar regions, insinuating between brain structures. Conversely, epidermoid cysts in intraparenchymal or intradiploic locations are very rare, accounting for less than 5% of all intracranial epidermoid cysts [3]. Here, we report two cases of atypical epidermoid cysts; the irst case demonstrated an intraparenchymal epi- dermoid cyst while the second case showed an epidermoid cyst that invaded into the intradiploic space and surrounding structures. Comparison on the salient radiological features of typical and atypical epidermoid cysts is emphasized. 2. Patient 1 A 47-year-old male with good past health was admitted for a one-month history of ataxia and headache. Plain CT brain (Figure 1(a)) showed an intra-axial hyperdense mass in the right cerebellar hemisphere with coarse calciic foci. he lesion was homogenous in appearance with lobulated margin with no appreciable enhancement ater IV con- trast (Figure 1(a)). Despite its size and mass efect (causing obstructive hydrocephalus), no signiicant vasogenic oedema was evident. On MRI, the lesion appeared markedly T2W hypointense and T1W hyperintense (Figure 1(b)), suggestive of either high proteinaceous content or subacute blood. No luid restriction was demonstrated in the difusion weighted images (DWI) and corresponding apparent difusion coef- icient (ADC) images (Figure 1(c)). Intraoperative indings showed extremely thick gelatinous substance, and histolog- ical examination of the surgical specimen showed cyst lining made of attenuated squamous epithelium and dystrophic cal- ciication along with keratinous debris, indings compatible with an epidermoid cyst (Figure 1(d)). he patient recovered well following surgery and had no neurological sequelae. 3. Patient 2 A 37-year-old male with good past health was admitted for progressive unsteady gait for six months. CT brain Hindawi Publishing Corporation Case Reports in Radiology Volume 2015, Article ID 528632, 4 pages http://dx.doi.org/10.1155/2015/528632