Intracranial growing teratoma syndrome (iGTS) is a rare phenomenon in patients with non-germinomatous germ cell tumor (NGGCT) after chemotherapy or radiotherapy. It manifests as paradoxical growth of teratomatous components, with multiple cystic lesions on cranial imaging despite normalized tumor markers. This paper presents a 22-year-old male with iGTS, diagnosed one month after chemotherapy against NGGCT. Initially diagnosed with presumptive pineal NGGCT causing obstructive hydrocephalus, the patient underwent endoscopic third ventriculostomy and extraventricular drainage with tumor biopsy followed by two chemotherapy cycles. Despite normalization of tumor markers, follow-up MRI showed increased tumor size with honeycomb-like cystic patterns. The patient underwent suboccipital craniotomy for tumor removal via combined telovelar and infratentorial supracerebellar approaches.The final pathology confirmed mature teratoma. However, postoperative bleeding and left thalamic infarction occurred, resulting in severe neurological deficits. Despite challenges, the patient eventually regained the ability to follow simple commands. To understand iGTS pathophysiology, several hypotheses, including the differentiation of immature components and the uninhibited growth of mature components induced by chemotherapy or radiotherapy, were explored. Surgical intervention remains as an ideal treatment, while clinical trials investigate chemotherapy options. Frequent imaging followups are crucial for early detection in iGTS for NGGCT patients.

Intracranial growing teratoma syndrome (iGTS) is a rare phenomenon in patients with non-germinomatous germ cell tumor (NGGCT) after chemotherapy or radiotherapy. It manifests as paradoxical growth of teratomatous components, with multiple cystic lesions on cranial imaging despite normalized tumor markers. This paper presents a 22-year-old male with iGTS, diagnosed one month after chemotherapy against NGGCT. Initially diagnosed with presumptive pineal NGGCT causing obstructive hydrocephalus, the patient underwent endoscopic third ventriculostomy and extraventricular drainage with tumor biopsy followed by two chemotherapy cycles. Despite normalization of tumor markers, follow-up MRI showed increased tumor size with honeycomb-like cystic patterns. The patient underwent suboccipital craniotomy for tumor removal via combined telovelar and infratentorial supracerebellar approaches.The final pathology confirmed mature teratoma. However, postoperative bleeding and left thalamic infarction occurred, resulting in severe neurological deficits. Despite challenges, the patient eventually regained the ability to follow simple commands. To understand iGTS pathophysiology, several hypotheses, including the differentiation of immature components and the uninhibited growth of mature components induced by chemotherapy or radiotherapy, were explored. Surgical intervention remains as an ideal treatment, while clinical trials investigate chemotherapy options. Frequent imaging followups are crucial for early detection in iGTS for NGGCT patients.

Intracranial growing teratoma syndrome (iGTS) is a rare phenomenon in patients with non-germinomatous germ cell tumor (NGGCT) after chemotherapy or radiotherapy. It manifests as paradoxical growth of teratomatous components, with multiple cystic lesions on cranial imaging despite normalized tumor markers. This paper presents a 22-year-old male with iGTS, diagnosed one month after chemotherapy against NGGCT. Initially diagnosed with presumptive pineal NGGCT causing obstructive hydrocephalus, the patient underwent endoscopic third ventriculostomy and extraventricular drainage with tumor biopsy followed by two chemotherapy cycles. Despite normalization of tumor markers, follow-up MRI showed increased tumor size with honeycomb-like cystic patterns. The patient underwent suboccipital craniotomy for tumor removal via combined telovelar and infratentorial supracerebellar approaches.The final pathology confirmed mature teratoma. However, postoperative bleeding and left thalamic infarction occurred, resulting in severe neurological deficits. Despite challenges, the patient eventually regained the ability to follow simple commands. To understand iGTS pathophysiology, several hypotheses, including the differentiation of immature components and the uninhibited growth of mature components induced by chemotherapy or radiotherapy, were explored. Surgical intervention remains as an ideal treatment, while clinical trials investigate chemotherapy options. Frequent imaging followups are crucial for early detection in iGTS for NGGCT patients.

Intracranial growing teratoma syndrome (iGTS) is a rare phenomenon in patients with non-germinomatous germ cell tumor (NGGCT) after chemotherapy or radiotherapy. It manifests as paradoxical growth of teratomatous components, with multiple cystic lesions on cranial imaging despite normalized tumor markers. This paper presents a 22-year-old male with iGTS, diagnosed one month after chemotherapy against NGGCT. Initially diagnosed with presumptive pineal NGGCT causing obstructive hydrocephalus, the patient underwent endoscopic third ventriculostomy and extraventricular drainage with tumor biopsy followed by two chemotherapy cycles. Despite normalization of tumor markers, follow-up MRI showed increased tumor size with honeycomb-like cystic patterns. The patient underwent suboccipital craniotomy for tumor removal via combined telovelar and infratentorial supracerebellar approaches.The final pathology confirmed mature teratoma. However, postoperative bleeding and left thalamic infarction occurred, resulting in severe neurological deficits. Despite challenges, the patient eventually regained the ability to follow simple commands. To understand iGTS pathophysiology, several hypotheses, including the differentiation of immature components and the uninhibited growth of mature components induced by chemotherapy or radiotherapy, were explored. Surgical intervention remains as an ideal treatment, while clinical trials investigate chemotherapy options. Frequent imaging followups are crucial for early detection in iGTS for NGGCT patients.