Purpose or Case Report: To report an unusual case of synchoronous primary brain tumours of two different histological subtypes in the posterior fossa of a 13 year old girl.
Methods & Materials: An otherwise well 13 year old girl presented following an 8 month history of headache, which had increased in severity in the 2 weeks prior to presentation. Initial MRI demonstrated an abnormality in the posterior fossa with unusual morphology. In the left cerebellar hemisphere was a well circumscribed, FLAIR hyperintense ovoid nodule which demonstrated no restricted diffusion and negligible post contrast enhancement. Adjacent, within the inferior vermis was an irregular mass which showed different signal characteristics, with differentiating features being contrast enhancement and restricted diffusion. In addition, there was leptomeningeal enhancement within the posterior fossa and along the spinal cord. No discrete nodular metastates. On biopsy, the lesions were of two distinct histological subtypes. The circumscribed nodule was a pilocytic astrocytoma with biphasic architecture and Rosenthal fibres, WHO grade I. The adjacent, more irregular mass was a WHO IV Medulloblastoma with classical histological subtype, and non-WNT, non-SHH molecular subgroup by immunohistochemistry.
Results: The presence of synchronous primary brain tumours is rare, with fewer than 5 cases reported in the paediatric population. To our knowledge, there have been no previous reports of synchronous posterior fossa tumours with different histological type. Inherited genetic syndromes such as neurofibromatosis type 1, neurofibromatosis type 2, Li-Fraumeni syndrome, tuberous sclerosis complex, Cowden disease and Turcot sydrome can predispose to tumours of the central nervous system. NF1 and NF2 can be assocatied with multiple CNS tumours. Other predisposing factors for multiple CNS tumours include previous radiotherapy and trauma. Our patient had no relevant past medical history and there were no clinical or genetic features of an underlying tumour predisposition syndrome.
Conclusions: Unique teaching point: While a rare entity, the signal characteristics of the two adjacent lesions allowed a prospective suggestion that dual pathology was present. In this case, the most discriminatory MR features were the DWI and post contrast signal characteristics, which differed between the synchronous WHO I astrocytic and WHO IV embryonal tumours.