Background: Pineal tumors are uncommon tumors that affect <1% of adults, with 50% of them being germinomas. A combination of endoscopic third ventriculostomy (ETV) and tumor biopsy is usually used. Cerebral vasospasm in association with aneurysmal subarachnoid hemorrhage (aSAH) has been extensively studied. However, at least according to the research, this is not the case in intraventricular hemorrhage (IVH) cases. We present a case with two distinct findings: (1) an unexpected large IVH following the removal of an external ventricular drain (EVD) in a patient who had undergone ETV and tumor biopsy, resulting in severe clinical vasospasm and (2) incidental pineal region germinoma regression on follow-up magnetic resonance imaging (MRI) without any prior adjuvant chemoradiation to explain such regression. Case Description: The authors describe an 18-year-old male patient who had a routine, uneventful combined ETV and tumor biopsy, as well as the placement of an EVD. Histopathological examination revealed germinoma. His postoperative course was complicated by IVH after EVD removal, which resulted in clinical vasospasm. Without any prior adjuvant chemoradiation, follow-up MRI of the b rain revealed a significant reduction in the size of the germinoma as well as reconstitution of the patency of the previously obstructed aqueduct of Sylvius. Conclusion: The take-home message from this case is that in the case of postoperative clinical deterioration in a patient with concurrent IVH and ETV, a high index of suspicion for vasospasm is required, as this may allow a significant amount of blood to pass down to the basal cisterns. Early detection and management of clinical vasospasm are critical for a better neurological outcome. Furthermore, unexpected tumor size changes can occur due to a variety of factors, so recent preoperative MRI of the brain should be obtained in the lead-up to surgery, and postoperative computed tomography should be used sparingly to avoid radiation-related tumor changes.