Accurate diagnosis and staging is required to guide therapy. Diagnosis is based on the combination of clinical symptoms, tumor markers, neuroimaging characteristics as well as cytological and histological confirmation. CT scan and/or magnetic resonance imaging (MRI) scan of the brain and spine with Gd-DTPA should be performed. Leptomeningeal spread is not uncommon at diagnosis (Aoyama 2009; Calaminus et al. 2005). Many studies with large patient numbers include both germinoma and NGGCT (Matsutani et al. 1997; Sawamura et al. 1998; Aoyama et al. 1998; Sano et al. 1989), and the exact rate of leptomeningeal spread specifically for NGGCT is not readily available in these studies. In the studies with relatively small number of patients, screening for detection of leptomeningeal disease is inconsistently performed (Kim et al. 2012; Ogawa et al. 2003; Robertson et al. 2014). According to a recent report which used modern MRI imaging for spinal leptomeningeal spread, it is reported to be as high as 22% (Korean Society of Pediatric Neuro-Oncology group study, unpublished data). Lumbar puncture for examination of human chorionic gonadotropin-beta (β-hCG) and α-fetoprotein (AFP) should be performed along with cerebrospinal fluid (CSF) cytology. Examination of serum AFP and β-hCG are also required. CSF level of tumor markers are more sensitive and reliable for diagnosis than serum level. Due to the common presentation of endocrinopathies, a thorough endocrine evaluation at the time of diagnosis is highly recommended (Thakkar et al. 2013). Imaging is not reliable to distinguish germinomas from NGGCTs, and diagnosis is made either by tissue confirmation or tumor markers. Tumor markers can be more sensitive than changes in images (Jorsal and Rorth 2012) and can be used during treatment to assess tumor response. It is highly controversial whether a tissue biopsy is mandatory for ICGCT because many patients with ICGCT can be correctly diagnosed without a tissue biopsy if demographic and radiological data were combined with serum/CSF tumor markers. In the recent COG study, patients with elevation of serum or CSF β-hCG >100 IU/L or any elevation of serum and CSF AFP >10 ng/mL are considered as NGGCT. The SIOP CNS germ cell tumor study uses >50 IU/L and >25 ng/mL as cut-off values for β-hCG and AFP, respectively, however, a biopsy is regarded as mandatory if marker levels are ≤50 IU/L (total HCG) or ≤25 ng/mL (AFP) in order to exclude the possibility of any malignant component in tumors (https://www.skion.nl/workspace/uploads/2_siop_cns_gct_ii_final_version_2_15062011_unterschrift_hoppenheit.pdf). There are pitfalls in diagnosing NGGCT on the basis of elevated tumor markers without a histologic diagnosis. Using an ultrasensitive enzyme immunoassay (EIA) method or a quantitative measurement of β-hCG mRNA in tumor tissues (Takami et al. 2015), Japanese investigators showed that some pure germinomas and at least some NGGCTs produce β-hCG. In that study, germinomas with syncytiotrophoblastic giant cells and those located other than at midline structures of the brain were associated with higher β-hCG levels. There are occasional patients with biopsy-proven germinoma who initially presented with mild elevation of AFP below reference level and recur with a mixed malignant component. Patients with mildly elevated AFP need to be carefully watched particularly if biopsy was not performed at the time of diagnosis. More emphasis is now being given in taking tissue biopsy before treatment starts. More standardized cut-off value needs to be adopted for diagnosis of NGGCT especially with serum and CSF β-hCG. When treatment is completed, routine physical and neurologic examinations are carried out every 3–6 months after treatment. Follow-up MRI is generally carried out every 6 months for the initial 5 years after treatment or more frequently for tumors which do not show complete response to treatment, and then once a year.

Obstructive hydrocephalus is frequently observed in the patient with ICGCT. Diagnosis of accompanying hydrocephalus and its management is the initial step in the treatment of patients with ICGCT. Intravenous mannitol can alleviate symptoms of increased intracranial pressure (ICP). Although corticosteroids are commonly used for the management of brain edema associated with tumors, they are less helpful for ICGCT because brain edema is less prominent for intraventricular tumors than for parenchymal tumors. If obstruction of the CSF pathway is evident in MRI and/or CT, surgical diversion of the CSF is required after initiation of mannitol and corticosteroid administration. For tumors located in the pineal area, endoscopic third ventriculostomy (ETV) is the treatment of choice to relieve the increased ICP. ETV can be performed simultaneously with an endoscopic tumor biopsy. For suprasellar tumors, ETV is rarely attempted because the tumor mass blocks the third ventricular floor. If a large suprasellar GCT occludes both foramina of Monro and causes severe hydrocephalus, an endoscopic septostomy is recommended with tumor biopsy. The procedure should be followed by a temporary extraventricular drainage (EVD) if surgical resection is planned (as is common for NGGCTs), or by a permanent ventriculoperitoneal shunt if chemotherapy or radiation therapy is scheduled (as is common for germinomas) for definite treatment of the tumor. If only one foramen of Monro is occluded, an endoscopic septostomy with tumor biopsy may be sufficient.