A previously healthy 10-year-old boy is brought to the emergency department for the evaluation of one episode of vomiting and severe headache since this morning. His mother says he also had difficulty getting dressed on his own. He has not had any trauma. The patient appears nervous. His temperature is 37°C (98.6°F), pulse is 100/min, and blood pressure is 185/125 mm Hg. He is confused and oriented only to person. Ophthalmic examination shows bilateral optic disc swelling. There is an abdominal bruit that is best heard at the right costovertebral angle. A complete blood count is within normal limits. Which of the following is most likely to confirm the diagnosis?

High-dose dexamethasone suppression test

A 10-year-old boy is brought to the emergency department by his parents because of a dull persistent headache beginning that morning. He has nausea and has vomited twice. During the past four days, the patient has had left-sided ear pain and fever, but his parents did not seek medical attention. He is from Thailand and is visiting his relatives in the United States for the summer. There is no personal or family history of serious illness. He is at the 45th percentile for height and 40th percentile for weight. He appears irritable. His temperature is 38.5°C (101.3°F), pulse is 110/min, and blood pressure is 98/58 mm Hg. The pupils are equal and reactive to light. Lateral gaze of the left eye is limited. The left tympanic membrane is erythematous with purulent discharge. There is no nuchal rigidity. Which of the following is the most appropriate next step in management?

Intravenous ceftriaxone and clindamycin therapy

Intravenous cefazolin and metronidazole therapy

A 12-year-old boy is brought to the emergency department after he vomited and said he was having double vision in school. He also says that he has been experiencing morning headaches, nausea, and dizziness over the last month. He has no past medical history and is not taking any medications. Physical exam reveals a broad-based gait, dysmetria on finger-to-nose testing, and nystagmus. Both serum and urine toxicology are negative, and radiography reveals a solid mass in the midline cerebellum that enhances after contrast administration. Biopsy of this lesion reveals cells of primitive neuroectodermal origin. Which of the following would most likely be seen on histology of this lesion?

Tooth enamel-like calcification

Foamy cells and high vascularity

An inconsolable mother brings her 2-year-old son to the emergency room after finding a large amount of bright red blood in his diaper, an hour ago. She states that for the past week her son has been having crying fits while curling his legs towards his chest in a fetal position. His crying resolves either after vomiting or passing fecal material. Currently, the child is in no apparent distress. Physical examination with palpation in the gastric region demonstrates no acute findings. X-ray of the abdominal area demonstrates no acute findings. His current temperature is 36.5°C (97.8°F), heart rate is 93/min, blood pressure is 100/64 mm Hg, and respiratory rate is 26/min. His weight is 10.8 kg (24.0 lb), and height is 88.9 cm (35.0 in). Laboratory tests show the following: RBC count 5 million/mm3 Hematocrit 36% Hemoglobin 12 g/dL WBC count 6,000/mm3 Mean corpuscular volume 78 fL What is the most likely underlying embryological cause predisposing to this condition?

Failure of the vitelline duct to close

Failure of the vitelline duct to open

Elevated anti-mitochondrial antibodies

Problem with bilirubin conjugation

Brain tumors in children for USMLE Step 3: High-Yield Pediatrics Lessons

Overview - The Little Brains

Most common solid tumors in childhood & the second most common malignancy after leukemia.
Primary tumors are more frequent than metastases.
Location is key: ~70% are infratentorial (posterior fossa), unlike adult tumors which are mainly supratentorial.
Presents with signs of ↑ Intracranial Pressure (ICP):
- Morning headaches, often occipital
- Projectile vomiting without nausea
- Papilledema (late sign)

⭐ The most common pediatric brain tumor is Pilocytic Astrocytoma (WHO Grade I), typically found in the cerebellum.

Clinical Features - Telltale Signs

Signs of ↑ Intracranial Pressure (ICP): The most common presentation.
- Headache: Classically worse on waking, improves after vomiting.
- Vomiting: Often projectile, without nausea.
- Papilledema: Optic disc swelling on fundoscopy.
- Cushing's Triad (Late): Hypertension, bradycardia, irregular respiration.
Age-Specific Signs:
- Infants: Macrocephaly, bulging fontanelle, suture diastasis, "sunsetting" sign.
- Older Children: School failure, personality changes, growth failure.
Location-Specific Signs:
- Cerebellar: Ataxia, Nystagmus, Dysmetria (📌 A.N.D.).
- Supratentorial: Seizures, hemiparesis, visual field defects.
- Brainstem: Multiple cranial nerve palsies, gait disturbance.

⭐ The triad of morning headache, vomiting, and ataxia is highly suggestive of a posterior fossa tumor.

Signs of increased intracranial pressure in infants

Tumor Types - Rogues' Gallery

Most common solid tumors in children. Location is key: ~60% are infratentorial (posterior fossa).

Tumor Type	Key Features & Histology	Location
Pilocytic Astrocytoma (Grade I)	- Most common pediatric brain tumor. - Biphasic pattern: dense fibrillary areas + loose microcystic areas. - Rosenthal fibers (eosinophilic corkscrew bodies). - GFAP positive.	Cerebellum
Medulloblastoma (Grade IV)	- 2nd most common; most common malignant type. - Small, round, blue cells. - Homer-Wright rosettes. - Highly radiosensitive.	Cerebellum (Vermis)
Ependymoma	- Arises from ependymal cells lining ventricles. - Perivascular pseudorosettes. - Often presents with hydrocephalus.	4th Ventricle
Craniopharyngioma	- From Rathke's pouch remnants. - Bimodal age distribution (5-14 yrs & 50-74 yrs). - "Wet keratin" & dystrophic calcification. - Cholesterol-rich, "machine oil" fluid.	Suprasellar

⭐ High-Yield: Medulloblastoma is the most common malignant brain tumor of the posterior fossa in children and has a tendency to disseminate via CSF (drop metastases).

Diagnosis & Management - The Battle Plan

Imaging: MRI with gadolinium contrast is the gold standard for diagnosis & surgical planning.
Histopathology: Biopsy or surgical resection provides definitive diagnosis & grading.
Supportive Care: Dexamethasone to ↓ vasogenic edema; manage hydrocephalus with VP shunt.

MRI of posterior fossa brain tumor in a child

⭐ High-Yield Fact: Radiotherapy is typically avoided or delayed in children < 3 years of age to prevent severe, long-term neurocognitive deficits. Chemotherapy is often used as a bridge (neoadjuvant therapy) in these young patients.

High‑Yield Points - ⚡ Biggest Takeaways

Most common solid tumors in children; second most common malignancy after leukemia.

Majority are infratentorial (posterior fossa), unlike in adults.

Pilocytic astrocytoma is the most common type; often low-grade.

Medulloblastoma is the most common malignant tumor, located in the cerebellum.

Classic triad of ↑ Intracranial Pressure: morning headache, vomiting, and papilledema.

Craniopharyngiomas: Supratentorial tumors from Rathke's pouch remnants causing visual defects.

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Brain tumors in children