Radiological and Biochemical Diagnosis of a Primary Mediastinal Germ Cell Tumour: A Case Report.

Anterior mediastinal masses pose a diagnostic challenge due to the non-specific presentation and overlapping clinical features, which may prolong investigations and delay diagnosis. This case describes a previously fit and well young man who presented with symptoms initially suspected to be caused by a respiratory infection. Following referral from primary care to the emergency department for non-improving respiratory symptoms, a chest X-ray demonstrated a large abnormality in the left hemithorax. A subsequent contrast-enhanced CT thorax revealed a large anterior mediastinal mass causing significant compression of the left lung, with associated pulmonary nodules suspicious for metastatic disease. Serum tumour markers demonstrated a markedly elevated alpha-fetoprotein (AFP), with moderate elevation of lactate dehydrogenase (LDH) and beta-human chorionic gonadotrophin (β-hCG). A CT abdomen and pelvis showed no further disease, and a testicular ultrasound demonstrated no focal testicular abnormality, supporting a primary mediastinal origin of the mass. The combined radiological and biochemical findings were diagnostic of a primary mediastinal non-seminomatous germ cell tumour, allowing urgent oncological treatment with cisplatin and etoposide chemotherapy to be initiated prior to final histopathological confirmation. A tissue sample obtained via ultrasound-guided biopsy confirmed the primary lesion to be a pleomorphic, yolk-sac tumour. The patient was then subsequently transferred to a tertiary specialist centre where he was treated with curative-intent carboplatin, bleomycin, vincristine, cisplatin and etoposide (CBOP-BEP) chemotherapy. A promising biochemical response to initial management was demonstrated with a decline in tumour markers, namely, AFP.  This case highlights the increasingly central role of integrating multimodal imaging with serum tumour markers in the assessment of complex anterior mediastinal masses, enabling prompt oncological decision-making in aggressive disease.