Unusual MR Imaging Features in CT Hyperdense Posterior Fossa Dermoids: Report of Two Cases

Abstract

Dermoids, either intracranial or in the rest of the body, usually have typical imaging findings due to their fat contents as fat density in computed tomography (CT) and T1- and T2-hyperintensity in magnetic resonance imaging (MRI). Variable imaging appearances have been described due to soft tissue contents, hair, calcification, or even tooth. Posterior fossa dermoids have been reported as a specific variant that shows hyperdensity in CT and mixed signal intensity in MRI. We report two cases of posterior fossa CT hyperdense dermoids that showed unusual MRI features in the form of signal loss in magnetization transfer images and lipid peak in magnetic resonance spectroscopy. Both patients underwent surgical resection and histopathological confirmation and the causes of this unusual imaging appearance are discussed.

Hemifacial spasm caused by multiple vascular attachments due to remote compression effects of a dermoid cyst in the cerebellar hemisphere: illustrative case

“…Observations Dermoid cysts in the lateral posterior fossa are extremely rare, and they are located close to occipital bone at the asterion, intradural space, and cerebellar hemisphere. [3][4][5][6][7][8] These cases are summarized in Table 1. Clinical symptoms of patients with these lesions included headache, ataxia, hearing loss, gait disturbance, dizziness, vertigo, and trigeminal neuralgia.…”

“…4 However, it is surprising that dermoid cysts originating from cerebellar parenchyma demonstrate not only a dural defect but also skull bone erosion. 3,7 If a dermoid cyst originates from true cerebellar parenchyma, it should destroy surrounding parenchyma, which is softer than such hard structures. Therefore, in the present case, it is believed that the dermoid cyst originated from the diploic space of the occipital bone, destroyed the dura mater, and compressed the cerebellar parenchyma.…”

“…1,2 Dermoid cysts located laterally in the posterior fossa are extremely rare. [3][4][5][6][7][8] The lesion is very slow growing and presents with clinical symptoms in early adulthood. Clinical symptoms depend on the location of the lesion.…”