Intradiploic epidermoid cyst of the skull
A 46 years old female, presented with a history of chronic headache, mainly on the left occipital region, which had increased in severity and frequency recently. Patient had no neurological deficits.
Contrast enhanced computed tomography revealed large expansile non-enhancing intradiploic hypodense lesion within the squamous part of left side of occipital bone (Fig. a,b). Magnetic resonance image revealed non enhancing lesion with heterogeneous hyperintense matrix. Diffusion weighted imaging and apparent diffusion coefficient revealed intense diffusion restriction which confirms the nature of the tumor (Fig. c,d,e,f,g).
Epidermoid cysts are benign, slow-growing lesions and may often reach an enormous size without producing neurological symptoms. Less than 1% of cranial tumors are epidermoid tumours, of which 75% are intradural and 25% are intradiploic in location. Intraparenchymal extension of intradiploic epidermoids is known to occur. Both CT and MR imaging modalities enable the preoperative diagnosis of these tumors with good accuracy.
CT is superior for assessment of density of lesion, extent of involvement of the inner and outer tables and presence of calcification. MRI is superior to CT in demonstrating lesions that have associated parenchymal involvement and lesions that do not have associated bone destruction.
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