Suprasellar Germinoma

Abstract

The most common germ cell tumor of the suprasellar region is the germinoma. A suprasellar germinoma can be a primitive tumoral lesion or a metastatic lesion from a pineal germinoma. Germinomas are most commonly seen in adolescents and young adults: 90 % of patients are younger than 20 years. There is no gender preference for the suprasellar location, unlike the pineal location with male predominance. Clinical symptoms include diabetes insipidus, precocious puberty, or growth failure related to hypothalamic involvement and visual loss provoked by chiasmatic compression. Large lesions can cause hydrocephalus by obstruction of the interventricular foramens. Tumoral markers such as α-fetoprotein and human chorionic gonadotropin (HCG) can be found in the serum and/or CSF. In the case of suggestive clinical and radiological patterns with presence of tumoral markers, the diagnostic biopsy can be avoided. Infundibular thickening and absence of the posterior lobe bright spot on T1WI are the more precocious radiological signs, and at this stage can simulate an inflammatory process, Langerhans cell histiocytosis, or lymphocytic infiltration (Fig. 31.1). As it grows, the lesion appears as a well-delineated round or lobulated lesion, isointense or hyperintense to gray matter on T1WI and isointense to hyperintense on T2WI (Fig. 31.2), with hyperintense necrotic foci in some cases. Calcifications, better seen on CT than on MRI, are not unusual but less frequent than in the pineal location. After gadolinium injection there is a marked and mostly speckled enhancement. The origin within the optic nerve or optic chiasm is very rare. Intraventricular extension in lateral ventricle and infiltration of the basal ganglia and the corpus callosum can occur (Fig. 31.3). Multifocal germinomas usually involve the pineal gland and the suprasellar cistern, simultaneously or not (Fig. 31.4). Leptomeningeal spread with drop metastases along the spinal cord are reported. ADC is usually decreased. MR spectroscopy shows markedly elevated choline with diminished N-acetyl aspartate. Despite the aggressive MRS pattern, a good response is observed in most cases after radiotherapy and chemotherapy. Before treatment, a complete survey of the brain and spinal canal is required because germinomas can metastasize by subarachnoid seeding. Negative MRI in children with diabetes insipidus does not exclude germinoma (Fig. 31.5). A repeat MRI examination is required in 3–6 months. Early diagnosis may reduce the risk of dissemination and the morbidity of treatment. The limited differential diagnosis includes craniopharyngioma with a more heterogeneous appearance associated with cysts, solid components and calcifications, and hypothalamic-chiasmatic glioma rarely associated with diabetes insipidus (see Chap. 30).