Cystic atypical choroid plexus papilloma, WHO grade II.
Choroid plexus tumors are rare tumors, seen mostly in children, where they comprise 2-4% of all brain tumors in the pediatric age group (10). The most common variant is choroid plexus papilloma (CPP), corresponding to WHO grade I tumors. Morphologically they grow in a papillary pattern with fibrovascular cores lined by a single layer of cuboidal to columnar cells with minimal pleomorphism, and have a sparse mitotic count. Complete surgical resection is the treatment of choice and is associated with an excellent prognosis. In contrast; choroid plexus carcinomas (CPC), correspond to WHO grade III, are aggressive tumors and have a dismal prognosis. They are characterized by areas of solid growth pattern, marked pleomorphism, increased mitotic count and necrosis. Brain invasion can be seen in all grades and per se, would not warrant a more aggressive behavior according to the WHO classification.
The presence of some tumors that are intermediate between CPP and CPC has only been recently included in the WHO classification. Patients with atypical CPP are significantly younger than other tumors (10). These atypical tumors show a papillary growth pattern with minimal pleomorphism. However; they tend to exhibit an increase in the mitotic count of ~2/10HPFs (3). The presence of occasional features of malignancy as seen in CPC is accepted although not required for making this diagnosis. In addition, proliferative marker Ki67 and p53 staining are intermediate between the benign and the malignant counterparts (10). Surgical excision is the treatment of choice in these patients. Chemotherapy is preserved for cases with recurrence or metastatic development.
The cystic variant of choroid plexus tumors was first recognized by Hoenig et al in 1967(2). Since then, only a few cases have been reported (1, 4, 5, 7, 8). Many of these tumors are seen in infants and are considered congenital in some cases. Occasionally, these lesions are discovered during routine antenatal screening(5). Acute hydrocephalus due to obstruction of CSF pathway can be a serious primary presentation, which if not treated urgently can result in sudden death (4, 8).
Radiologically; there is a large cystic mass with or without a mural nodule, located in the medial portion of the cyst wall(9). The nodule enhances after contrast medium injection. However, in the absence of such nodules, the cyst wall enhances instead. The content of the cyst is identical to CSF. All cases described so far have been of CPP (1). Treatment included total excision of the mural nodule and the cystic wall which resulted in complete cure (1).
The radiological differential diagnosis for a cystic tumor with an enhancing mural nodule includes pilocytic astrocytoma, hemangioblastoma, pleomorphic xanthoastrocytoma, meningioma and ganglioglioma(9). In the absence of a tumor nodule, choroid cyst comes into the differential diagnosis(6). Pathologically; cystic CPP's without a mural nodule are lined by cuboidal and elongated columnar epithelium with atypical nuclei, increased cellularity and positive Ki-67 immunostain(4). Another pathological differential diagnosis is papillary ependymoma, which shows GFAP strongly positive fibrillary cores in the absence of basement membrane. Yolk sac tumor is also an important consideration in this age group. However; these tumors are located in the midline, contain eosinophilic globules and are positive for α fetoprotein. As with all pediatric brain tumors, approach to management should be discussed within a multidisciplinary team. Choroid plexus tumors are extremely rare and calls for international collaboration should be considered.
Contributed by Maysa Al-Hussaini, MD, Izzeddin Bakri, MD, Maisa Swaidan, MD, Usama Jumaily, MD, Najyah Abuirmeileh, MD