The differential diagnosis of the occipitally located tumor included meningeal metastasis of the known adenocarcinoma. However, the tumor was comprised of three germ layers with mesenchymal neuroectodermal and endodermal tissue corresponding to a mature teratoma. Teratomas within the central nervous system (CNS) are scarce tumors with a reported incidence of 0.006 per 100.000 per year and with a fraction of 82 % representing nonmalignant teratomas (9). Matsutani and colleagues showed that mature teratomas make up to 12.4 % of intracranial germ cell tumors. In their study, the age of analyzed patients was 11.6 +/- 8.5 years (mean +/- standard deviation) with nearly all cases located in the pineal region (17/19) and all patients being male (8). A recent study reported 35/43 CNS teratomas being pediatric (?16 years), while 8 cases were adults (4). The pediatric teratomas were localized in the spinal cord (23/35) and intracranially (12/35). 8/12 intracranially located cases represented mature teratomas and were localized in the third ventricle, frontobasally or occipitally (4). The latter localization was sometimes associated with an encephalocele (4). Mature CNS teratomas occurring in adults are an absolute rarity with only few reports existing in the literature. Localizations are described within the spine, the sellar region, the occipital lobe and the pineal region (12), (1), (2). Only single case reports present adult patients with mature teratomas of the posterior fossa (3, 10), underlining the sparsity of our case.
Vermis aplasia and the enlarged posterior fossa reported here are both part of the Dandy-Walker Malformation (DWM). DWM is a rare congenital disorder that was initially reported as a triad of cystic dilatation of the fourth ventricle, vermis hypoplasia and hydrocephalus (11), but can present with a variety of morphologic features and clinical symptoms (5). Typically, DWM patients display severe neurological symptoms in early childhood, and the majority of patients show associated neural malformations (5). Our patient was adult and did not report on any neurological symptoms. We did not detect any abnormalities in the forebrain. Instead, a teratoma was attached to the meninges that had a bridge-like connection to the cerebellum, suggesting that this tumor was part of the malformation. While single DWM cases have been reported with co-occuring lipomas, hamartoma, neurocutaneous melanosis or dermoid cysts (5), (7), (6), the here presented case is, to our knowledge, the first report showing a combination of DWM and a teratoma, which should be taken into consideration when observing similar phenomena on MR imaging.
Contributed by Julia Pöschl, Frank Berger, Hans Kretzschmar and Ulrich Schüller