Regresses Epidermoid Cyst Manifesting as Lytic Skull Lesion

Dear Editor,

Differential diagnosis of calvarial lesions is important in order to decide whether biopsy, surgical intervention, or follow-up is required for further management [1]. A 33-year-old female presented with the complaint of recently noticed depression over the vertex. It was not associated with pain or fever. There was no history of trauma. There was around 5×5 cm ill-defined depression without any local tenderness on features of inflammation (Figure 1). The skin over the depression was healthy and could be moved freely. CT scan bone window showed a lesion with irregular outer table (Figure 1). There was no evidence of calcification or periosteal reaction. Rest of the skull was unremarkable. Cerebral parenchyma was normal. A differential diagnosis of multiple myeloma and histiocytosis was considered. Blood investigations were normal. The patient was planned for the biopsy of the lesion. Through a small curvilinear incision, the lesion was exposed. There was presence of thin membrane attached to the outer table; it was taken for biopsy (Figure 2). Bone was irregular but healthy. The microscopic examination revealed the membrane to be composed of stratified squamous keratinized epithelium (Figure 2). There were no areas of calcification or hemorrhage. The post-operative course of the patient was uneventful and the patient was doing well at follow-up. Epidermoid cysts are thought to result from a displacement of ectodermal tissue during the third to fifth week of embryogenesis [2]. Epidermoid tumours account for less than 1% of the cranial tumors. Out of these, 75% are located intradurally and 25% are located within the diploic spaces [3, 4]. Usually these lesions present in the third or fourth decade of life as a long-standing painless subcutaneous scalp swelling covered with normal skin [3]. The most common presentation of the calvarial epidermoid is a long-standing, asymptomatic lump on the head [5]. Surgical excision is the preferred treatment for diagnosis, to relieve any symptoms and for cosmetics with the goal being total removal of the capsule [1-3,5]. Spontaneous regression of epidermoids and dermoids of the calvarian bones has been reported during early childhood [6]. In this case, probable regression of the small cyst brought attention of the patient towards the lesion and as the lesion was a lytic skull lesion in a young adult; the patient underwent biopsy of the lesion to confirm the diagnoses and it showed to be the epidermoid cyst.

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