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Hydatidosis is an endemic affection in Morocco. Cerebral echinococcosis is a relatively rare entity accounting for only 1-2% of all hydatid cysts in humans. hydatid cyst of the posterior fossa is a very uncommon site for the disease. We report the case of a 12 year-old child admitted for high intracranial pressure. Brain CT scan showed a posterior fossa cyst without enhancement after contrast medium injection. Operative finding revealed a hydatid cyst. The histological examination of the tissue sample confirmed the diagnosis. The patient was given albendazole post operatively. He feels well six months later., Competing Interests: Les auteurs ne déclarent aucun conflit d’intérêt.

Dandy-Walker malformation (DWM) is the most common human cerebellar malformation, characterized by hypoplasia of the cerebellar vermis, cystic dilation of the fourth ventricle, and an enlarged posterior fossa with upward displacement of the lateral sinuses, tentorium, and torcular. Although its pathogenesis is not completely understood, there are several genetic loci related to DWM as well as syndromic malformations and congenital infections. Dandy-Walker malformation is associated with other central nervous system abnormalities, including dysgenesis of corpus callosum, ectopic brain tissue, holoprosencephaly, and neural tube defects. Hydrocephalus plays an important role in the development of symptoms and neurological outcome in patients with DWM, and the aim of surgical treatment is usually the control of hydrocephalus and the posterior fossa cyst. Imaging modalities, especially magnetic resonance imaging, are crucial for the diagnosis of DWM and distinguishing this disorder from other cystic posterior fossa lesions. Persistent Blake's cyst is seen as a retrocerebellar fluid collection with cerebrospinal fluid signal intensity and a median line communication with the fourth ventricle, commonly associated with hydrocephalus. Mega cisterna magna presents as an extraaxial fluid collection posteroinferior to an intact cerebellum. Retrocerebellar arachnoid cysts frequently compress the cerebellar hemispheres and the fourth ventricle. Patients with DWM show an enlarged posterior fossa filled with a cystic structure that communicates freely with the fourth ventricle and hypoplastic vermis. Comprehension of hindbrain embryology is of utmost importance for understanding the cerebellar malformations, including DWM, and other related entities.

Rosette-forming glioneuronal tumor (RGNT) of the fourth ventricle is a rare, recently described WHO Grade I neoplasm. The authors report 6 examples of RGNT arising primarily from the cerebellar vermis. All the patients were female, and the mean age of presentation was 24.8 years. The original diagnoses included pilocytic astrocytoma, ependymoma, cerebellar dysembryoplastic neuroepithelial tumor (DNT), and oligodendroglioma. The cases showed classic pathological characteristics, although in 2 cases the lesions included DNT-like "floating neurons" involving Purkinje cells, a feature which has not been previously reported to the authors' knowledge. The clinical outcome was excellent with no recurrences after complete resection. These cases expand the known clinical and histological spectrum of this rare tumor type. Given the lack of fourth ventricle involvement in most of these cases, the authors suggest revising the name to RGNT of the posterior fossa.

A 10-year-old boy was admitted with a 4-month history of ataxic gait, headache, vomiting and diplopia. The headaches had worsened in month 4 and were associated with vomiting during head movement. Cranial computed tomography (CT) and magnetic resonance imaging (MRI) scans revealed a hydatid cyst located in the posterior fossa. The patient underwent suboccipital craniotomy and a cerebellar hydatid cyst (approximately 5 cm in diameter) was removed using Dowling's technique. The diagnosis was confirmed during surgery and by histological examination of a tissue sample from the cyst. The patient was treated with the antihelmintic agent albendazole in combination with antibiotics. The post-operative course was uneventful and the patient was discharged after 1 week. In conclusion, when a cystic lesion is detected on CT or MRI scans, hydatid disease should be taken into consideration in countries where hydatid infestation is endemic.