T1 pre-gad T1 post-gad T1 post-gad

Diagnosis: Pilocytic astrocytoma with neurofibromatosis type I

Neurofibromatosis type I is an autosomal dominant phakomatos seen on chromosome 17 which is associated with cafe au lait spots, low grade astrocytomas, optic nerve gliomas, cerebral aneurysms, plexiform neurofibromas, white matter and basal ganglia hamartomatus lesions, hypoplastic sphenoid wing among many others. Optic nerve glioma is the most common CNS tumor in NFI and occurs in up to 15% of cases. Twenty five percent of all patients with optic nerve glioma have NF1. Pilocytic astrocytoma is one of the low grade astrocytomas seen in neurofibromatosis type I. They typically appear in children or young adults and are usually located around the third or fourth ventricles in the region of the hypothalamus or the optic chiasm. Another common location is in the cerebellar hemisphere. They are usually histologically benign lesions; however, up to 1/3 may be clinically aggressive. Leptomeningeal dissemination has been reported. On CT and MR the classic appearance is of a cystic mass which is hypointense on T1 and bright on T2 with an enhancing mural nodule. Calcification occurs in 10% of pilocytic astrocytomas. Hydrocephalus is a complication of pilocytic astrocytoma and is dependent upon the size and location of the mass.

Neurofibromatosis type II on the other hand is typically associated with bilateral acoustic schwannomas and is much less common. It is transmitted as an autosomal dominant trait on chromosome 22. Percutaneous manifestations of NF2 are unusual. Other lesions seen in NF2 include meningiomas, cord ependymomas, and intracranial calcification. Without the other stigmata of neurofibromatosis type 1 as seen in this patient, the differential diagnosis of a cystic lesion in the midbrain with an enhancing mural nodule should include, in addition to pilocytic astrocytoma; metastasis, particularly in an older age group, ganglioglioma and hemangioblastoma. This location is not typical of hemangioblastoma as most of these are located in the cerebellar hemispheres.

This patient has multiple stigmata of neurofibromatosis type I including optic nerve glioma, which may have spread into the optic radiations on the right best seen on the T2 weighted axials. The focus of increased signal in the periatrial white matter on the left is non- specific but may represent a hamartomatous lesion. The enhancing soft tissue adjacent to the left EAC which is barely visible on this images is actually a plexiform neurofibroma. In addition, the enlargement of the third and lateral ventricles with increased T2 signal in the periventricular white matter is compatible with hydrocephalus and transependymal resorption of CSF. This patient had known neurofibromatosis type I without a family history. The pilocytic astrocytoma was resected. Related Cases

Pou Serradell A; Central lesions in neurofibromatosis: clinical, MRI and histopathologic correlations. An attempted classification. Rev Neuol, 1991, 1471(1) p17-27.

Palma L, Guidetti B, Cystic pilocytic astrocytoma of the cerebral hemispheres. Surgical experience with 51 cases and long-term results. J Neurosurg, Jun 1985; 62(6) p811-5.

Strong JA, Hatten HP, Brown MT; Debatin JF, Friedman HS, Oakes WJ, Tien R. Pilocytic astrocytoma: correlation between the initial imaging features and clinical aggressiveness. AJR Aug 1993; 161(2) p369-72.















































Hemangioblastoma Neurofibromatosis Optic nerve glioma