venerdì 28 settembre 2007
Figure 1: Axial noncontrast CT scan demonstrates a lobulated mass of increased attenuation arising from the pineal gland. This is causing dilatation of the lateral and third ventricles.
Figure 2: Sagittal T1 demonstrates a lobulated mass arising from the pineal gland of slightly decreased signal intensity when compared to grey matter.
Figure 3: Axial FLAIR image shows mild increased signal in the region surrounding the pineal mass, representing edema.
Figure 4: Sagittal postcontrast T1 demonstrates heterogenous enhancement, which is mostly peripheral, of a pineal mass. Subtle leptomeningeal enhancement along the anterior aspect of the brainstem and the cerebral vermis is also seen.
Figure 5: Axial postcontrast T1 demonstrates heterogenous enhancement, which is mostly peripheral, of a pineal mass. Obstructive hydrocephalus is present with mild ventricular dilatation.
Diagnosis: Pineal germinoma
Pineal region tumors account for only 0.3-2.7% of intracranial tumors with germinomas making up the largest portion of the region’s tumors, approximately 40%. Additionally, germinomas are the most common of the germ cell tumors, with a large portion, 90%, presenting in patients less than 20 years of age. They tend to show a substantial male predominance. Patients with pineal germinomas may present with Parinaud syndrome (upward gaze paralysis with altered convergence). Additionally, diabetes insipidus can be a presenting sign with suprasellar germinomas prior to abnormal imaging findings.
Germinomas are more frequently located in the suprasellar region (50-60%), and less commonly located in the pineal region (30-40%). This is in contradistinction to the commonly held opinion that they occur more frequently in the pineal region. Synonyms for germinoma include: dysgerminoma, extra-gonadal seminoma, and atypical teratoma.
NECT scan of a germinoma usually reveals a mildly hyperattenuating mass that may have calcifications in or around the tumor. Both contrast enhanced CT and MRI will demonstrate intense enhancement (which is often speckled in appearance on MRI). Iso to hyperintense signal is seen on both T1 and T2 weighted MRI images. The tumor marker PLAP (Placental Alkaline Phosphatase) tends to be elevated in both the serum and the CSF of patient’s with a germinoma.
Several important diagnoses should be considered when faced with pineal region pathology. Pineal parenchymal tumors, pineoblastomas and pineocytomas, may demonstrate calcifications in or around the tumor, however this occurs three to four times more frequently with germinonas. Other lesions to consider in the differential include other germ cell tumors and tectal gliomas. Serum and CSF tumor markers, including ß-HCG and alpha-fetoprotein, may be beneficial in narrowing the differential.
Dissemination of germinomas arising from both locations into the CSF is common. Consequently, MRI of the entire neuroaxis is recommended prior to surgery. Germinomas have a relatively good prognosis because of their sensitivity to radiation and chemotherapy; 5-year survival approaches 90%.