Presentation
Two month history of headaches, sometimes nauseated/vomiting. New onset diplopia. On examination has bilateral hyperemic, swollen discs.
Patient Data
Lobulated midline posterior fossa abnormality. Inferiorly, the lesion protrudes through the foramen magnum. It is predominantly high attenuation but there are components that are calcified and other areas with relatively low attenuation. There is minimal perilesional edema. There is mass effect with effacement of the 4th ventricular outflow tracts, flattening of the brainstem and effacement of the prepontine and quadrigeminal plate cisterns.
There is obstructive hydrocephalus with dilatation of the third ventricle recess evident and some periventricular low attenuation compatible with transependymal CSF spread.
No subarachnoid or intraventricular hemorrhage.
There is a vessel extending inferiorly from the region of the straight sinus along the posterior margin of the abnormality close to the calcified regions. It is not clear if this is an artery or vein. No other abnormal vessels. The dural venous sinuses appear patent allowing for the phase of enhancement.
Right frontal approach external ventricular drain.
The midline posterior fossa lesion is well-defined and lobulated. It has predominantly low signal on T2 and FLAIR and high intrinsic T1 signal and non enhancing. There is a component inferomedially which shows high T2w signal and enhancement. There are areas of susceptibility artefact posteriorly which probably represent a mixture of calcification and blood products based on the mixed signal on the phase map.
There is central low T1w signal in the partially imaged cervical spinal cord, which probably represents a syrinx.
Surgical resection pathology report
Much of the specimen consists of altered blood clot but there are fragments of gliotic cerebellar tissue within which there is a large cystic lesion. This lesion is lined by epithelium and the epithelium varies between simple cuboidal ciliated epithelium to stratified squamous epithelium, although the epithelium is not keratinizing. Goblet cells are occasionally noted. Hair shafts and glandular structures are also identified, as is bone and adipose tissue. The cyst has clearly ruptured and there is a foreign body giant cell reaction including cholesterol clefts.
Comment
The appearances are of a mature teratoma which has ruptured resulting in hemorrhage. There are no malignant elements identified in the tissues examined.
Posterior fossa lesion - Ruptured mature teratoma.
Case Discussion
Unusual posterior fossa abnormality. Initially it was thought to be a hemorrhage secondary to a vascular abnormality given the high attenuation and areas of calcification. However, the patient had a 2 month history. There is minimal perilesional edema, which would be unusual for hemorrhage. There is also pronounced obstructive hydrocephalus with marked dilatation of the third ventricular recesses. This degree of hydrocephalus is unlikely to have occurred acutely, particularly because the patient was relatively well.
The MR signal characteristics are not in keeping with a spontaneous hemorrhage. Rather most of the lesion appears cystic with presumably proteinaceous material. There is a solid enhancing component and areas of calcification, potentially fat and blood products.
The midline location, apparent slow growth and mixed solid cystic lesion with calcified components suggest a teratoma.