The imaging appearance of a cauliflower-like hypervascular intraventricular mass plus a more irregular and hypercellular component with CSF dissemination, in a child, strongly suggested a choroid plexus carcinoma. The differential diagnosis included a germ cell tumor, but bloodwork did not reveal any suggestive biomarkers. Other considerations included intraventricular glioblastoma, intraventricular ependymoma, and primitive neuroectodermal tumor. Given the evidence of CSF dissemination, total spinal imaging was also performed as part of the initial staging (as well as follow-up studies), which did not reveal a definite distant deposit.

The patient underwent craniotomy for partial resection (to be followed by chemotherapy and craniospinal radiotherapy).

Pathology report:

High-grade neoplasm with choroid plexus differentiation and embryonal morphology, suggestive of choroid plexus carcinoma.

Sections show a densely cellular biphasic tumor with two distinct components. One consists of sheets of markedly pleomorphic and discohesive cells with scant cytoplasm consistent with a primitive neuronal or embryonal appearance, with scattered bizarre and multinucleated giant cells. Mitotic figures are frequent and necrosis is present. The other component consists of complex papillary epithelioid structures resembling choroid plexus, with scattered mitotic figures, including atypical mitoses. The transition between these two components is mostly abrupt, with some foci showing a gradual transition.

Immunohistochemical staining performed on block A3 shows that both components of the tumor are diffusely positive for synaptophysin. S100, AE1.3/CAM5.2 and MNF116 predominantly highlight the choroid plexus component and are largely negative in the poorly differentiated component, with some scattered positivity for keratins. There is strong and diffuse p53 nuclear labeling seen in both the poorly differentiated portion as well as the epithelial component. There is focal GFAP and desmin positivity and focal weak staining for transthyretin in the choroid plexus component, while the poorly differentiated component is negative. INI1 and BRG1 show retained nuclear staining throughout (consistent with wildtype). EMA, Oct3/4 and SALL4 are negative.

The overall morphology and immunophenotype are consistent with a choroid plexus neoplasm, suggestive of choroid plexus carcinoma (a WHO grade 3 neoplasm), however, the presence of a primitive/embryonal component is unusual in this context and may affect the biological behavior of this tumor (perhaps resembling a WHO grade 4 neoplasm).

Molecular diagnostics revealed variants in TP53, PTEN, and RB1. Genetic testing for germline TP53 mutations was negative.