Clinical, radiological, and pathological features of 24 atypical intracranial epidermoid cysts.

Object: Most intracranial epidermoid cysts typically present with long T1 and T2 signals on MR images. Other epidermoid cysts with atypical MR images are often misdiagnosed as other diseases. In this study the authors aimed to analyze the incidence and the clinical, radiological, and pathological features of atypical epidermoid cysts.

Methods: Among 428 cases of intracranial epidermoid cysts that were surgically treated between 2002 and 2008 at Beijing Tiantan Hospital, cases with an atypical MR imaging appearance were chosen for analysis. Clinical and pathological parameters were recorded and compared in patients with lesions demonstrating typical and atypical MR appearance.

Results: An atypical epidermoid cyst accounts for 5.6% of the whole series. Radiologically, 58.3% of atypical epidermoids were misdiagnosed as other diseases. Compared with a typical epidermoid cyst, atypical epidermoid lesions were significantly larger (p = 0.016, chi-square test). Pathologically, hemorrhage was found in 21 patients with atypical epidermoid cyst and is significantly correlated with granulation (p = 0.010, Fisher exact test). Old hemorrhage was found in 13 cases and was significantly correlated with cholesterol crystals. Twenty-one patients were followed up for 1.3-8.6 years after surgery. The 5- and 8-year survival rates were both 100%. Three patients experienced cyst recurrence. The 5- and 8-year recurrence-free rates were 95% and 81.4%, respectively.

Conclusions: Radiologically, an atypical epidermoid cyst should be differentiated from dermoid cyst, teratoma, schwannoma, glioma, craniopharyngioma, and cavernous angioma. A tendency toward spontaneous hemorrhage is confirmed in atypical epidermoid cysts, and a hypothesis was proposed for spontaneously intracystic hemorrhage in atypical epidermoid cysts. Follow-up confirmed long-term survival of patients with atypical epidermoid cysts.