Posterior Fossa Calcifying Pseudoneoplasm of the Neuraxis (CAPNON): Presentation of Three Surgical Cases.

Background: Calcifying pseudoneoplasm of the neuraxis (CAPNON) is an extremely rare entity with fewer than 150 cases reported in the literature and mostly with a supratentorial or spinal location. Posterior fossa CAPNON has been reported scarcely, and association with perilesional edema is a topic not yet approached which might play a significant role in treatment decision and clinical progression. Our objective is to report, to our knowledge, the first series of 3 posterior fossa CAPNON surgically treated in a single institution and assess features that help provide a systematic approach to diagnosis and timely treatment.

Methods: This was a monocentric, retrospective study of surgical patients diagnosed with a posterior fossa CAPNON in the last 5 years. A thorough bibliographic research was conducted.

Results: Three patients were included. Locations involved IV ventricle, right cerebellopontine angle with extension to foramen magnum, and cerebellar vermis. Two of them presented with symptoms linked to acute hydrocephalus, and the other one presented with progressive cranial nerve palsy and brainstem compression signs. The 3 of them showed radiological signs of perilesional edema on their preoperative magnetic resonance imaging. Gross total resection was accomplished in one case, with near and subtotal resections in the others. There were no complications. The outcome was favorable in all cases.

Conclusions: It is essential to contemplate this infrequent diagnosis in cases of calcified lesions involving the posterior fossa. When symptoms manifest, surgery should be considered. Perilesional edema could be associated with symptomatic progression and hence a sign suggesting the need for surgical treatment.