Intracranial germ cell tumors (IGCTs) represent a rare and heterogeneous group of central nervous system neoplasms, sharing clinical and histopathological features with their more common gonadal counterparts [1]. Germinomas, also referred to as pure seminomas, account for approximately 0.2% - 1.7% of all primary intracranial tumors [2]and constitute nearly 60% of intracranial germ cell tumors, predominantly arising in the pineal and suprasellar regions [3]. In nearly 90% of cases, they occur before the age of 20 years [4][5], with a marked male predominance and a sex ratio of 2:1 [6]. Germinomas are characterized by high radiosensitivity, marked chemosensitivity, and a propensity for dissemination through the cerebrospinal fluid (CSF) pathways [7].

Radiological diagnosis may occasionally be misleading, as heterogeneous pineal masses can mimic teratomas. Therefore, histopathological and immunohistochemical confirmation remains essential to establish the diagnosis of pure intracranial germinoma and guide appropriate therapeutic decision-making.

We report the case of a 17-year-old adolescent presenting with a pineal mass initially suspected to be a ruptured mature teratoma, ultimately diagnosed as a non-secreting pure intracranial germinoma following stereotactic biopsy, and treated with BEP chemotherapy followed by panventricular radiotherapy, resulting in mass stabilization and favorable clinical evolution.

Germ cell tumors arise predominantly in the gonads, while their occurrence within the central nervous system remains exceptional [10]. Among these, germinomas—also referred to as dysgerminomas or pure seminomas—account for approximately 60%. They primarily affect children and young adults, with the highest incidence during the second decade of life (45%) [11], and most commonly originate in the pineal gland or suprasellar region [3]. Tumor dissemination or the presence of multiple nodular implants along the lateral and third ventricles is observed in about 10% of cases [6].

Although pineal localization is typical, the radiological presentation of these tumors may be misleading, particularly when differentiating them from teratomas, which are far more heterogeneous and often contain fatty or cystic components. Neuroimaging (CT/MRI) of pineal tumors lacks sufficient specificity to reliably distinguish a germinoma from a teratoma, as some germinomas may present with calcifications or atypical heterogeneity mimicking a teratomatous lesion [12]. In our case, the initial imaging strongly suggested a ruptured pineal teratoma due to the presence of fat density areas and intralesional calcifications. Histological and immunohistochemical confirmation was decisive: the dense lymphocytic infiltrate, together with the specific expression of germ cell markers (PLAP+, CD117+, SALL4+), enabled a definitive diagnosis of pure germinoma. This case underscores the importance of clinico-radiological correlation and the use of stereotactic biopsy to avoid diagnostic errors in midline germ cell tumors.

Pineal germinomas typically cause a relatively rapid onset of symptoms, mainly due to compression of the aqueduct of Sylvius and secondary obstructive hydrocephalus. Patients classically present with headaches, nausea, vomiting, visual disturbances, and sometimes transient vision loss or oculomotor abnormalities, as widely described in the literature [13]. In our observation, the patient exhibited this typical constellation of symptoms—progressive headaches, vomiting, seizures, and decreased visual acuity—consistent with the usual clinical presentation of pineal germinomas and highlighting the central role of intracranial hypertension as the revealing manifestation.

Intracranial germinomas are often characterized histologically by a dense lymphocytic infiltrate composed predominantly of T lymphocytes, but also including B lymphocytes, plasma cells, and numerous macrophages. This feature may lead to an initial misdiagnosis, such as encephalitis or T-cell lymphoma, particularly when only a small biopsy sample is available [14]. Although the initial biopsy suggested a differential diagnosis between encephalitis and lymphoma, these hypotheses had already been considered clinically. The progressive evolution of symptoms, the large size of the pineal mass on imaging, and the absence of systemic infectious signs made encephalitis unlikely. Likewise, the patient’s adolescent age and the radiological appearance of the lesion were less typical of lymphoma. These considerations justified the prompt performance of a stereotactic biopsy, which enabled a definitive diagnosis of pure germinoma through immunohistochemical analysis.

Diagnostic confirmation therefore relies heavily on immunohistochemistry, which enables the identification of specific markers such as PLAP, CD117, and SALL4 (13). In our case, these markers were decisive in confirming the pure seminomatous nature of the tumor despite the abundance of lymphocytes. PLAP (placental alkaline phosphatase) is a classical marker of germ cells, CD117 (c-KIT) is characteristically expressed by undifferentiated germ cells, and SALL4 is a transcription factor expressed in pure germ cell tumors. The co-expression of these three markers is therefore highly indicative of a pure intracranial germinoma, allowing it to be distinguished from other germ cell or lymphoproliferative tumors [15][16].

Intracranial germinomas are well known for their high sensitivity to both chemotherapy and radiotherapy, which allows excellent clinical outcomes even in the presence of large tumors or ventricular extension [17]. Due to the lack of specific recommendations in major oncology guidelines—namely NCCN and ESMO, which do not provide dedicated protocols for primary intracranial germ cell tumors—management is typically guided by European and international expert consensus statements such as the EANO/SNO/EURACAN recommendations [17]. These generally advocate induction chemotherapy followed by tailored radiotherapy depending on tumor volume and the risk of ventricular or leptomeningeal dissemination.

In our case, the patient received three cycles of BEP chemotherapy (bleomycin, etoposide, cisplatin) followed by pan-ventricular radiotherapy (24 Gy) with a 16 Gy local boost, consistent with established evidence regarding the chemosensitivity and radiosensitivity of intracranial germinomas. For instance, in a series of 60 patients with localized intracranial germinomas, neoadjuvant chemotherapy followed by 40 Gy focal radiotherapy resulted in significant tumor regression and high event-free survival, while underscoring the importance of field design to reduce periventricular relapse [18]. Similarly, the prospective non-randomized SIOP CNS GCT 96 study, which included 190 patients with localized germinomas, compared the efficacy of chemotherapy followed by 40 Gy focal radiotherapy with that of craniospinal irradiation (24 Gy) plus a 16 Gy tumor boost without chemotherapy [19]. These studies collectively support the role of induction chemotherapy in reducing tumor volume and enabling a more conservative radiotherapy approach while ensuring effective tumor control.

The prognosis of intracranial germinomas is generally favorable, with reported 5-year overall survival rates exceeding 90%, owing to their high responsiveness to therapy. Nonetheless, close surveillance is essential, incorporating clinical evaluation, imaging, and biological monitoring (serum markers and cerebrospinal fluid when appropriate) to detect potential recurrences or late treatment-related complications. Although follow-up strategies vary across protocols, published data support intensive monitoring during the first two years, followed by progressively more spaced evaluations in cases of sustained stability [17].

Furthermore, the long-term implications of therapeutic choices must be considered, particularly in adolescents. The BEP regimen carries risks of gonadal, pulmonary, and renal toxicity, whereas panventricular radiotherapy may lead to late neurocognitive, endocrine, or vascular effects. Given the potential risk to fertility, the patient underwent sperm preservation beforehand, after being informed of the possible impact of treatment. In our case, no late complications have been observed to date, but prolonged follow-up remains essential to allow early detection of potential late toxicities.

Nevertheless, it should be emphasized that conclusions drawn from a single case remain limited, and larger series or prospective studies would be required to confirm the generalizability of these observations.

This case illustrates a pure germinoma of the pineal region in an adolescent, initially mimicking a mature teratoma with intraventricular rupture on imaging. The initial histological findings were non-specific, underscoring the diagnostic challenge and the critical importance of immunohistochemistry. Combined treatment with BEP chemotherapy and pan-ventricular irradiation resulted in a favorable clinical and radiological outcome. The publication of this case is relevant due to its distinctive diagnostic and therapeutic features.