4.1 Central Nervous System Tumors

Central nervous system (CNS) tumors are the most common solid tumors of childhood. Leukemia remains the most common pediatric cancer overall, but when the question is a mass, the brain and spinal axis lead. CPHON Test Content Outline (TCO) II.A items on CNS tumors test whether you can localize the lesion from the history, keep the workup from causing herniation, nurse hydrocephalus, recognize posterior fossa syndrome, explain risk-adapted radiation, and name late effects. Do not invent a single most-common-CNS-tumor percentage. Medulloblastoma is among the most common malignant pediatric CNS tumors; low-grade gliomas are common as well. The exam cares more about compartment and nursing traps than about a pie chart.

Posterior fossa versus everything above the tentorium

Posterior fossa tumors sit below the tentorium cerebelli. Three histologies dominate bedside teaching:

• Medulloblastoma typically arises in the cerebellar vermis in school-age children, fills the fourth ventricle, and can seed the neuraxis through cerebrospinal fluid (CSF). Staging therefore includes the entire spine, not only the head.
• Cerebellar astrocytoma, often a pilocytic astrocytoma, classically forms a cyst with a mural nodule. Many are surgically curable; they still cause hydrocephalus and ataxia while they occupy the posterior fossa.
• Ependymoma often grows from the floor of the fourth ventricle. Children vomit, tilt the head, and develop obstructive hydrocephalus. Residual disease after surgery drives local-control decisions.

Supratentorial tumors sit above the tentorium. They irritate cortex, so seizures, hemiparesis, and a drop in school performance or a personality change are the clues. A 9-year-old whose grades collapse and who develops a new focal seizure needs a brain-tumor workup, not a discipline referral.

Brainstem gliomas, including classic diffuse intrinsic pontine presentations, produce cranial-nerve palsies, long-tract signs, and ataxia. Early papilledema may be absent because CSF pathways can remain open until late. These tumors are rarely resectable in the way a cerebellar hemisphere mass can be.

Craniopharyngioma is a sellar and suprasellar tumor. Visual-field cuts, growth failure, and diabetes insipidus (DI) belong in the first sentence of the nursing plan. Sodium, urine output, and hormone replacement are not optional add-ons after the surgeon leaves.

Optic pathway gliomas are strongly associated with neurofibromatosis type 1 (NF1). A toddler with café-au-lait macules and declining vision needs magnetic resonance imaging (MRI) and ophthalmology, and chemotherapy is often preferred over radiation in very young children to spare developing brain, orbit, and cochlea.

Presentation: early clues versus late herniation

The intracranial-pressure history is a child who wakes with morning headache and vomiting that eases after sitting up. Night and morning are worse because recumbency raises venous pressure. Ataxia and a wide-based gait point to cerebellum. New diplopia, facial droop, a hoarse cry, or gag failure are cranial-nerve palsies and point toward brainstem. Seizures are more supratentorial. Infants show macrocephaly, a bulging fontanelle, sunset eyes, and irritability because sutures can still open. Behavior change and falling schoolwork are neurologic until proven otherwise.

Cushing triad—hypertension, bradycardia, and irregular respirations—is a late sign of herniation. Waiting for Cushing triad to confirm a brain tumor is how children code in the emergency department. A still-verbal 6-year-old with morning vomiting and ataxia already needs MRI and neurosurgery, not another week of sinus antibiotics.

Workup: MRI yes, lumbar puncture only when safe

MRI of the brain is the definitive imaging study. Add MRI of the entire spine when a disseminating tumor such as medulloblastoma is possible. CSF cytology completes neuraxis staging for embryonal tumors, but only after a neurosurgeon has cleared the risk. Do not perform a lumbar puncture (LP) in a child with mass effect or obstructive hydrocephalus. Dropping lumbar pressure beneath a tight posterior fossa can cause downward herniation.

Hydrocephalus is treated with an external ventricular drain (EVD) and, in some children, a later ventriculoperitoneal (VP) shunt. EVD nursing is a CPHON skill: keep the drip chamber at the ordered height relative to the tragus or other unit landmark; never raise or lower the system because the bed was moved; clamp only as ordered for transport; treat the circuit as sterile and closed; watch for overdrainage (low-pressure headache, extra-axial collections) and underdrainage (vomiting, bradycardia, declining mental status). After VP shunt placement, teach families malfunction: headache, vomiting, lethargy, swelling along the tract, or a return of sunset eyes. A febrile child with a shunt also needs infection in the differential.

Posterior fossa syndrome and radiation concepts

After medulloblastoma resection, posterior fossa syndrome (cerebellar mutism) often declares itself 1 to 2 days later, not in the post-anesthesia care unit. The child who spoke on the evening of surgery becomes mute or severely dysarthric, emotionally labile, hypotonic, and may stop swallowing. Protect the airway, involve speech-language pathology and feeding therapy, and prepare the family that recovery can take weeks to months and may be incomplete. This is not stubbornness after anesthesia, and it is not cisplatin ototoxicity presenting as speech arrest.

Risk-adapted craniospinal radiation (CSI) treats the whole neuraxis for tumors that seed CSF, especially medulloblastoma in children old enough to receive it. Boost doses go to the posterior fossa or residual beds. Proton therapy is a delivery method, not a different drug: the beam stops (Bragg peak) and can spare developing brain, cochlea, heart, and other exit-dose organs compared with older photon CSI. It does not erase late effects. Very young children, commonly younger than about 3 years, are treated with strategies that delay or avoid radiation because myelination and neurocognitive development are still underway. Chemotherapy may be used as a bridge. Do not teach that every pediatric brain tumor receives CSI on the day of diagnosis.

Chemotherapy toxicities and the long tail

Protocol chemotherapy for embryonal CNS tumors often includes vincristine and cisplatin. Vincristine neuropathy is constipation, jaw pain, foot drop, and lost reflexes. Cisplatin ototoxicity is high-frequency sensorineural hearing loss; serial audiograms are part of the roadmap. Pack-years are not relevant in this population. Do not import adult smoking arithmetic into a 7-year-old’s radiation record. Pediatric exposure language is radiation field and dose, cumulative platinum, and which endocrine organs sat in the beam.

Late effects after CNS tumor therapy include neurocognitive change (processing speed, attention, working memory—arrange 504 or individualized education program supports), endocrine deficits (growth hormone (GH), adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH) after hypothalamic-pituitary or CSI exposure), hearing loss, stroke-like vasculopathy after some fields, and secondary tumors in irradiated tissue. Survivorship clinic is not optional because hair grew back.

A 5-year-old with morning vomiting and a wide gait, a postoperative day-2 mute child after vermian resection, and a 2-year-old whose team is delaying CSI are the three CPHON pictures. Location, no LP through mass effect, EVD and shunt safety, posterior fossa syndrome, vincristine versus cisplatin toxicities, and GH/ACTH/TSH plus hearing surveillance will carry the items.