**Core Concept**
Medulloblastoma is a malignant brain tumor that primarily affects children, with a high propensity for metastasis. In pediatric patients, particularly those under 3 years old, the treatment approach often involves a combination of surgery, chemotherapy, and radiation therapy to achieve the best possible outcome.

**Why the Correct Answer is Right**
In the curative management of medulloblastoma, open surgery with the intention of leaving tumor margins intact is not an ideal approach. This is because medulloblastoma is a highly aggressive tumor that can easily infiltrate surrounding brain tissue, making complete surgical resection challenging. Leaving tumor margins behind can lead to recurrence and worsen the prognosis. Instead, surgeons aim to achieve a maximal safe resection of the tumor while minimizing the risk of neurological deficits.

**Why Each Wrong Option is Incorrect**
**Option B:** Chemotherapy is indeed a crucial component of curative therapy for medulloblastoma, particularly in pediatric patients. It is used to target microscopic disease and prevent recurrence.

**Option C:** Total cranial spinal irradiation is a common treatment modality in the management of medulloblastoma, especially in cases where the tumor has spread to the spine. It helps to eradicate any residual cancer cells and prevent further progression.

**Option D:** The placement of a ventriculoperitoneal (VP) shunt for obstructive hydrocephalus is often necessary in patients with medulloblastoma, especially those who have undergone surgical resection. Hydrocephalus can occur due to the tumor's location in the cerebellum, and a VP shunt helps to relieve the increased intracranial pressure.

**Clinical Pearl / High-Yield Fact**
In pediatric neurosurgery, the goal of tumor resection is not to achieve a perfect gross total resection but rather to balance the risk of recurrence with the risk of neurological deficits. This is particularly important in cases of medulloblastoma, where the tumor's aggressive nature demands a more nuanced approach.

**✓ Correct Answer: A. Open surgery with leaving the tumour margins**