Synchronous solitary calvarial yolk sac tumor metastasis as the initial presentation of mediastinal germ cell tumor.

Introduction: In children, malignant tumors presenting as a calvarial mass that too as initial manifestation are unusual. Also, brain metastases per se are rare in pediatric solid tumors with an incidence of just 1.5%.
Case Description: We present a child with calvarial metastasis which was the presenting symptom of an otherwise asymptomatic large malignant mediastinal germ cell tumor (GCT). The lesion was dural-based involving both calvaria as well as the underlying brain parenchyma. Despite such multicompartmental location, no obvious bony destruction was seen. A 12-year-old boy presented with progressively enlarging scalp swelling and features of raised intracranial pressure. The lesion was totally excised and calvarial defect reconstructed using titanium mesh. Though the preoperative chest computed tomography suggested teratoma, the histopathology of the cranial lesion was a yolk sac tumor (YST).
Conclusion: Initial manifestation of GCT as calvarial swelling, pure YST (with no other germ cell component), and the eccentric multicompartmental (dural based) location rather than usual midline GCTs is noteworthy. The report thus highlights an atypical presentation in GCT. Although uncommon, it is worthwhile to consider metastatic GCT as a differential among calvarial lesions.