Giant cystic choroid plexus papilloma mimicking intracerebral hydatid cyst.

PURPOSE: To present the rare case of a giant cystic choroid plexus papilloma masquerading as a hydatid cyst with a paradoxical clinical and radiological presentation. METHODS: This is the first case of a giant choroid plexus tumour within the lateral ventricle being clinically asymptomatic. This child presented incidentally after head trauma. Magnetic resonance imaging demonstrated an entirely cystic component with minimal engorgement of the anterior or posterior choroidal arteries and lack of vivid frond-like enhancement which are normally associated with choroid plexus papillomas. On the contrary, the lesion actually exhibited classical hallmarks of a hydatid cyst including 'floating membrane sign' with a distinct lack of perilesional oedema. RESULTS: Suspicion for a hydatid cyst mandated a surgical approach tailored to the goal of en bloc removal necessitating a larger craniotomy to facilitate the Dowling-Orlando hydrodissection technique. Preoperative albendazole was administered and 3% hypertonic saline soaked patties were available. These precautions were ultimately unnecessary given a thin-walled cyst was encountered bearing no resemblance to a hydatid cyst, with safe internal puncture and decompression followed by gross total resection possible without anaphylactic reaction. A convincing choroid plexus attachment was identified. Interestingly, massive blood loss often cautioned in choroid plexus papillomas was not encountered. CONCLUSION: It is imperative to consider hydatid cysts as a cause of giant intra-axial cysts given the disastrous consequences of anaphylactic shock if spillage occurs and this differential has not been considered. This is a rare case of an entirely cystic choroid plexus papilloma mimicking a hydatid cyst.