DIAGNOSIS: Papillary glioneuronal tumor (PGNT)
This is the 11th case of a PGNT reported in the literature (1, 2). In the revised WHO classification (3) this tumor is not included as a separate entitity, but only briefly mentioned as a rare variant of ganglioglioma. In the present case, clinical features were similar to those previously reported, including a short history of seizures and headaches. The average age at presentation had been found to be 27 years (1, 2), and the age of our patient was 24 years. The male:female ratio including our case is 0.8.
PGNTs have been reported to arise in all major cerebral lobes, and with one exception all contained a cystic element (1, 2). Radiologically, all tumors were well-demarcated. The size range was 1.5-7 cm, and only 3 large lesions ($ 6 cm) had been found associated with significant edema. In contrast to almost all other cases, the tumor in our patient showed no contrast-enhancement. Only the smallest tumor (1.5 cm) of all other reported PGNTs had also lacked contrast enhancement (2). As our reported tumor was of a similarly small size (1 cm), contrast enhancement in PGNTs as well as edema formation seem to be size-dependent. An additional radiological feature of PGNTs can be calcification, which was observed in 40% of the previous cases, but was absent in our case.
Histologically, the most striking feature was the clear immunohistochemical distinction between cells of neuronal and astrocytic differentiation. The pseudopapillary arrangement of actrocytic cells with the neuronal cells being interspersed in the interpapillary spaces is highly typical of papillary glioneuronal tumors, and the pseudopapillae have been considered the most architecturally distincive feature of PGNT (2). Other findings, that have been associated with the majority of PGNTs and were also found in our case are Rosenthal fibers and hemosiderin-laden macrophages in the surrounding reactive tissue (2).
Somewhat in contrast to the previously reported cases we did not observe prominent hyalinization of tumor vessels. Hyalinized vessels are also a common feature of several other glioneuronal neoplasms, such as ganglioglioma, neurocytoma, dysembryoplastic neuroepithelial tumor, pilocytic astrocytoma and pleomorphic xanthoastrocytoma. In all of these tumors hyalinized vessels may or may not be present. Our case is the first PGNT reported to lack conspicuous vessel hyalinization. Considering its small size, it is possible that the tumor was caught at a stage to early for prominent hyaline degeneration of vessel walls to develop.
Follow-up data on the patients reported so far ranged from 6 months up to 7 years (1, 2). Gross total tumor resection had been achieved in 9 cases, and partial resection in one, which was then irradiated. None of the tumors had recurred during the follow-up period. Likewise, also in our case the patient, who was operated in May 2000 showed no recurrence on scans taken in August 2000 and has remained free of symptoms. Thus, PGNTs uniformely appear to carry a good prognosis.
Contributed by Katrin Lamszus MD, Maria Makrigeorgi-Butera M.D., Rudolf Laas MD, Manfred Westphal M.D., Dimitrios Stavrou MD