A rare case of giant cerebral hemispheric colloid cyst - expect the unexpected.

Introduction: Colloid cysts are rare cystic tumors commonly located in the third ventricle. Extraventricular locations are rare, and only very few cases have been reported in the literature. These include the fourth ventricle, sellar region, cerebral hemisphere, cerebellum, brainstem, and velum interpositum. We are reporting a case of a giant right hemispheric colloid cyst. Case Description: A 75-year-old gentleman presented with complaints of difficulty in walking, swaying, and mild memory disturbances with subtle left pyramidal type of weakness. The imaging studies revealed a giant cystic lesion in the right cerebral hemisphere that was T1 hypointense and T2 hyperintense with no contrast uptake. During surgery, the cyst was suspected to be a colloid cyst since it was filled with whitish viscous substance. The patient had a complicated postoperative period with focal seizures and delayed left side weakness and drowsiness which required readmission and prolonged hospital stay. Conclusion: Extraventricular locations of colloid cysts are rare. Our case of right cerebral giant colloid cyst represents a rare case posing a diagnostic and management dilemma. The case highlights that all care must be taken to ensure minimal cyst content spillage intraoperatively. Postoperative concerns include seizures, chemical meningitis, and acute encephalopathy-like picture which need careful assessment and tactical management.