Pediatric Posterior Fossa Tumors

01What Is a Pediatric Posterior Fossa Tumor?

The posterior fossa refers to the infratentorial, suboccipital compartment of the cranial vault, the region that contains the cerebellum and brainstem. It's the most common location for brain tumors in childhood. Most of these tumors develop when cells that would normally divide under tight control begin multiplying excessively instead. This happens sporadically in the large majority of children, without an underlying genetic condition, and without anything the family did or didn't do playing a role.

Three pathologies account for most tumors found in this location: pilocytic astrocytoma, medulloblastoma, and ependymoma. Each behaves differently, is treated differently, and carries a different long-term outlook, though surgery is the mainstay of treatment for all three, since none of these lesions can be left untreated. Rarer tumors, including epidermoid, dermoid, schwannoma, choroid plexus papilloma, and atypical teratoid/rhabdoid tumor (AT/RT), can also occur in this region.

02Classification

03Symptoms

The cerebellum controls balance, coordination, and smooth movement, so early symptoms usually reflect that. As the tumor grows, signs of increased pressure inside the skull tend to follow.

• Unsteady gait or imbalance
• Headaches that worsen in the morning
• Morning vomiting
• Coordination difficulties
• Abnormal eye movements
• Slowed or slurred speech

Headache, morning vomiting, and imbalance occurring together is an important warning sign and warrants prompt evaluation by a neurosurgeon.

04Diagnosis

Contrast-enhanced MRI is the standard first step in diagnosis. It shows the tumor's location and size, and whether it's obstructing the normal flow of cerebrospinal fluid. A definitive diagnosis is only reached after surgery, once the tissue has been examined under the microscope.

05Treatment Options — Overview

These tumors don't shrink on their own. Left untreated, they continue to grow and increase pressure on surrounding cerebellar and brainstem structures, which is why surgery is the standard first step rather than a choice to be weighed.

Large tumors can obstruct the narrow pathway through which cerebrospinal fluid normally flows, causing hydrocephalus. In most children, this resolves once the tumor is removed, without any further procedure. When hydrocephalus is severe enough to be life-threatening, a temporary drain is placed first to relieve the pressure; the tumor is then removed, and the drain is withdrawn within a few days. A permanent shunt is not the default approach here; it's reserved for the small number of children whose cerebrospinal fluid flow doesn't recover after surgery.

What follows surgery depends on the pathology result. In pilocytic astrocytoma, no further treatment is usually needed once the tumor has been completely removed. In medulloblastoma, surgery is followed by radiotherapy and chemotherapy, and how completely the tumor is removed at the first operation strongly influences the success of everything that follows. In ependymoma, radiotherapy follows complete removal. In both medulloblastoma and ependymoma, identifying the tumor's molecular subgroup also plays an important role in tailoring how intensive treatment needs to be.