Late finding of a dermoid cyst in a posterior fossa intra-axial lesion: A rare case report.

Background: Intracranial dermoid cysts are rare congenital inclusion cysts derived from ectodermal elements and account for a very small proportion of intracranial lesions. Although they are usually slow-growing and may remain clinically silent for years, they can become symptomatic once they exert mass effect or obstruct cerebrospinal fluid pathways. Posterior fossa involvement is uncommon, and delayed clinical presentation may occur despite long-standing lesion growth. This report describes a posterior fossa dermoid cyst causing obstructive hydrocephalus in an adolescent patient and highlights the radiological, histopathological, and surgical considerations relevant to its management. Case Description: The patient, a 16-year-old female, presented with a 3-year history of progressive visual impairment, daily vomiting, fatigue, and loss of appetite. Radiological studies, including computerized tomography and magnetic resonance imaging scans, revealed a midline cystic lesion within the fourth ventricle, leading to active obstructive hydrocephalus. Clinical manifestations included signs of increased intracranial pressure and fourth ventricle narrowing. Histopathological examination of tissue fragments from the cyst wall demonstrated a lining of squamous epithelium with evidence of parakeratosis. Furthermore, the necessity for careful consideration of surgical techniques is underscored, as dermoid cysts could exhibit adherence to arachnoid tissue. Intraoperatively, the lesion was approached through a posterior fossa craniotomy, and cyst decompression/ excision was performed with careful microsurgical dissection because the capsule was adherent to surrounding arachnoid and neural structures. Conclusion: This report emphasizes the significance of early diagnosis and surgical intervention in managing the intricate challenges posed by posterior fossa dermoid cysts.