Posterior fossa dermoid cyst.

Dear Sir,

A 2-year-old boy presented with opisthotonos and gait imbalance. The patient reported several episodes of vomiting over the last month. A sinus tract near the external occipital protuberance was also noted. Fundus examination showed bilateral papilledema. CT that ensued revealed a posterior fossa cystic lesion causing obstructive hydrocephalus [Figure 1]. An emergency external ventricular drain (EVD) was placed. Subsequent Magnetic resonance imaging (MRI) revealed a 50 × 35 × 35 mm cystic lesion behind the 4th ventricle with a 10 mm solid component. Given the presence of the sinus tract, dermoid cyst was the most likely diagnosis [Figure 1]. The patient was operated upon. A dermal sinus tract was identified that extended intracranially. The cyst wall was carefully mobilized and excised completely. Histological examination verified the presence of a dermoid cyst. Postoperative the patient was neurologically intact and the EVD was removed on postoperative day 8. On follow-up MRI carried out 4 months later, no cyst recurrence was noted.

Figure 1

(a) Computed tomography (CT) demonstrating a cystic lesion, compressing the 4th ventricle and causing obstructive hydrocephalus (b) (c–e) Magnetic resonance imaging (MRI) showing a cystic lesion with a 10-mm solid component. (f) Postoperative CT

Intracranial dermoid cysts are congenital benign neoplasms that account for 0.1–0.7% of all intracranial tumors.[12] Most intracranial cysts arise in the posterior fossa and they usually lead to neurological symptoms such as dizziness, headache, and meningitis during childhood. Patients with a posterior fossa dermoid cyst and an associated dermal sinus may develop bacterial meningitis or abscess formation of the dermoid itself.[1] Treatment of the posterior fossa dermoid cyst needs microsurgical excision. Total removal of the dermal sinus and the tumor is preferred in order to minimize the risk of recurrence or malignant transformation.[1]