Intracranial germinomas are diagnosed based on clinical presentation, neuroimaging characteristics, and histological examination [1]. Our patient presented with unusual clinical, radiological, and pathological findings of intracranial ectopic germinomas. The main complaint of the patient was dystonic movement of the right fingers. Brain imaging showed multiple lesions with cystic and solid components. Biopsy findings of granulomas with lymphocytic infiltration were unreasonable for germinoma.
Although there is no consensus, some hypotheses exist regarding the etiology of intracranial germinomas [1]. According to the germ cell theory, intracranial germinomas originate from neoplastic transformation of primordial germ cells that have migrated aberrantly and usually arise in midline structures, such as the pineal gland or suprasellar regions [1, 2]. Occasionally, germinomas originate from the basal ganglia and thalamus which is slightly off-midline because they spread along the ventricles [2, 4]. However, germinomas in the cerebral hemispheres, as in our patient, have rarely been reported [1, 2]. The etiology of ectopic germinoma is unclear; however, third ventricle development may induce ectopic primordial germ cells to migrate away from the midline or germ cells may directly move to the cerebral hemisphere during embryonic development [6].
Ectopic intracranial germinomas can have a variety of symptoms depending on their location [1]. Our patient initially presented with focal dystonia in the right finger. Focal dystonia may be caused by abnormal thalamic-to-premotor cortex input from lesions in the basal ganglia [7]. The most common symptoms in patients with germinomas in the basal ganglia are progressive cognitive decline and hemiparesis [8, 9]. However, focal dystonia without hemiparesis or cognitive decline has rarely been reported in basal ganglia germinoma [7].
The initial diagnosis is important to establish an appropriate treatment strategy for brain tumors. In our case, most parts of the tumor occurred in the intraparenchymal areas and basal ganglia without involvement of the pituitary and pineal gland, which lead to the initial diagnosis of other tumors such as astrocytoma, ependymoma, or primitive neuroectodermal tumor. However, a literature review revealed that germinomas should be considered as a possible diagnosis in adolescent patients with infiltrative parenchymal cystic tumors [6, 10].
Tumor biopsy is necessary for definitive diagnosis of intracranial neoplasms. In our patient, the preliminary neuropathologic results of the intraoperative consultation were granulomatous inflammation surrounding a few atypical cells. In the case of gonadal germinoma, a granulomatous reaction occurs, which is related to interferon-gamma and tumor necrosis factor-alpha secreted by T-cell [11–13]. Granuloma formation is rare in intracranial germinomas because of the presence of the blood-brain barrier and the absence of lymphatic reactions, but it may occur as an immune response [11–15]. Immunohistochemical staining for c-kit (CD117) and podoplanin (D2-40) is important for a definite diagnosis if granulomas are dominant but clinically suspected germinomas.
The present case indicates that ectopic germinomas can occur with unusual clinical manifestations of focal dystonia, radiologic images of intraparenchymal cystic lesions, and pathologic findings of granulomatous inflammation. Considering the good treatment response to chemoradiotherapy in germinomas, an accurate diagnosis using immunohistochemical staining is of paramount importance.