r. H. is a 42 year old left handed male who suffered a witnessed generalized seizure lasting 3-4 minutes. His past medical history was significant for ethanol abuse as well as being followed at an outside institution for the past three years for a seizure disorder. At the time of admission, his sole prescription medication was dilantin. Physical exam was notable only for a right parietal soft tissue hematoma. Neurological examination was normal. Blood tests obtained in the Emergency Room revealed no abnormality.
 
Imaging Findings
 

        Initial non-enhanced CT scan of the brain (Fig. 1a,b) demonstrated a 4.2 x 3.8cm left occipitoparietal cystic lesion without significant mass effect. Apart from a right parietal soft-tissue hematoma there was no acute intracranial traumatic injury identified. Following the injection of contrast (Fig 2a,b), there is identification of a 1 cm. enhancing nodule at the medial aspect of the lesion.
 
         On MRI (Fig. 3), the left occipitoparietal lesion is again noted with a homogeneous medial enhancing nodule again noted. There was no enhancement identified along the wall of the cyst. Of further note is that the signal intensity of the cystic component differs from that of clear fluid representing proteinaceous material (Fig. 3b).
 
Discussion
 
          In the pediatric population, the pilocytic astrocytoma is both the most common cerebellar neoplasm as well as the most common glioma overall- constituting 10% of all pediatric astrocytomas⁽³⁾. The quoted incidence rate within the adult population varies across studies, with 0.49 per million per year the incidence quoted in a recent British study specifically interested in adult pilocytic astrocytomas (Bell, 2004).

         One of the earliest features of pilocytic astrocytomas in the adult to be recognized was how the distribution of lesion location within the brain differed from the pediatric population. In children, the cerebellum was the most frequent site of tumor involvement (67%). In adults, however, Bell et al.⁽¹⁾ found that five of the ten patients over

Figure 1: A, Unenhanced axial CT scan image at the level of the basalganglia demonstrates a left occipital hypodense focus with a possible nodule at the medial aspect B, Unenhanced image slightly cephalad to (a) shows a well defi ned left parietoccipital cystic lesion that is slightly hyperdense to CSF.








Figure 2: a,b Contrast-enhanced CT matched images to Figure 1demonstrates homogeneous enhancement of the medial mural nodule with no signifi cant enhancement of the cystic component.

30 with pilocytic astrocytomas had supratentorial lesions and the remaining five had cerebellar lesions. Similarly, Burkhard et al⁽²⁾ found supratentorial involvement in 55% of adult patients. As would be expected from the diverse location of the lesions, the clinical presentation is varied depending on the site of the tumor.
 
The classic imaging manifestation of cerebellar and cerebral pilocytic astrocytoma is that of a cyst-like mass with an enhancing mural nodule and is seen in approximately two-thirds of cases. The cyst wall can