Pseudotumor Cerebri

Pseudotumor Cerebri, now more accurately termed Idiopathic Intracranial Hypertension (IIH), is a syndrome characterized by raised intracranial pressure (ICP) in the absence of a mass lesion, hydrocephalus, or abnormal cerebrospinal fluid (CSF) composition. Historically termed "benign intracranial hypertension," this name is now discouraged because the condition carries a significant risk of permanent visual loss if untreated.

Epidemiology

• Age: The condition is rare in children under 10 years of age (1 in 100,000–150,000).
• Gender: In prepubertal children, the gender distribution is equal. In post-pubertal adolescents and adults, there is a strong female preponderance.
• Obesity: While strongly associated with obesity in post-pubertal females, obesity is less common in prepubertal children with IIH.

Etiology

By definition, IIH has no identifiable cause. However, a similar clinical picture (Secondary Intracranial Hypertension) can be triggered by various factors, which must be ruled out:

1. Medications: Tetracyclines, Vitamin A derivatives (isotretinoin, excessive intake), growth hormone, nalidixic acid, and withdrawal of corticosteroids.
2. Systemic Disorders: Anemia, renal failure, Addison’s disease, hypoparathyroidism, and Systemic Lupus Erythematosus (SLE).
3. Venous Outflow Obstruction: Cerebral venous sinus thrombosis (CVST), mastoiditis, or transverse sinus stenosis.

Pathophysiology

The exact mechanism is poorly understood. Proposed theories include increased resistance to CSF absorption at the arachnoid granulations, increased CSF production, or elevated cerebral venous pressure. Recent research in adults suggests abnormal CSF androgen profiles or dysfunction of 11$\beta$-hydroxysteroid dehydrogenase type 1.

Clinical Features

Children are usually alert with no constitutional symptoms.

• Headache: The most frequent symptom. It is often chronic, progressive, frontal, and worsened by Valsalva maneuvers or changes in posture.
• Visual Disturbances:
  • Transient Visual Obscurations (TVO): Brief episodes of graying out of vision (seconds) precipitated by bending or standing.
  • Diplopia: Horizontal diplopia due to unilateral or bilateral sixth nerve (abducens) palsy, which acts as a false localizing sign of raised ICP.
• Pulsatile Tinnitus: A "whooshing" sound synchronous with the heartbeat.
• Papilledema: The hallmark sign. It is usually bilateral but can be asymmetric. In chronic cases, it can lead to optic atrophy and blindness.

Diagnosis

Modified Dandy criteria

A diagnosis of definite IIH requires all of the following criteria (A through E) to be met:

1. Papilledema (Criterion A): Presence of optic disc swelling.
2. Normal Neurologic Examination (Criterion B): The patient must have a normal neurologic status, with the specific exception of cranial nerve abnormalities (typically unilateral or bilateral sixth nerve palsy).
3. Neuroimaging Findings (Criterion C):
   • Brain MRI must show normal brain parenchyma without evidence of hydrocephalus, mass, or structural lesion.
   • There must be no abnormal meningeal enhancement.
   • Venous thrombosis must be excluded (preferably via MR Venography).
4. Normal CSF Composition (Criterion D): Normal cell count, glucose, and protein levels.
5. Elevated Opening Pressure (Criterion E):
   • Properly performed lumbar puncture (lateral decubitus position) showing elevated opening pressure.
   • Threshold: $\ge$ 280 mm H2O (28 cm H2O) is considered elevated for children and obese adults.

Diagnosis of IIH Without Papilledema

In the absence of papilledema, a diagnosis of IIH can be made if Criteria B through E are met, PLUS either:

• Unilateral or bilateral abducens (sixth) nerve palsy.
• OR (if no palsy is present) at least three of the following neuroimaging markers suggestive of raised ICP:
  1. Empty Sella: Pituitary gland flattened against the floor of the sella turcica.
  2. Globe Flattening: Flattening of the posterior aspect of the ocular globe.
  3. Optic Nerve Distention: Distention of the perioptic subarachnoid space $\pm$ a tortuous optic nerve.
  4. Venous Sinus Stenosis: Transverse venous sinus stenosis (often distal).

Important Considerations

• Neuroimaging: An MRI with MR Venography (MRV) is mandatory to rule out cerebral sinovenous thrombosis (CSVT), which is a secondary cause of intracranial hypertension.
• Secondary Causes: Before diagnosing Idiopathic IH, secondary causes such as medication use (tetracyclines, vitamin A derivatives, steroids), anemia, and endocrine disorders (Addison disease) must be excluded.

Management

The primary goals are to relieve symptoms (headache) and preserve vision.

General Measures:

• Weight loss is recommended for obese adolescents. Any potential offending medications (e.g., tetracyclines) should be discontinued.

Medical Therapy:

• Acetazolamide: The first-line drug (10–30 mg/kg/day). It is a carbonic anhydrase inhibitor that reduces CSF production.
• Topiramate: An alternative that provides headache prophylaxis and appetite suppression (beneficial in obesity).
• Corticosteroids: Generally not recommended for routine use but may be used temporarily in fulminant cases with rapid visual loss while awaiting surgery.
• Serial Lumbar Punctures: The diagnostic LP is often therapeutic, but repeated LPs are traumatic for children and rarely provide a long-term solution.

Surgical Therapy:

Indicated for refractory headaches or progressive visual loss despite medical therapy.

• CSF Diversion: Ventriculoperitoneal (VP) or Lumboperitoneal (LP) shunts.
• Optic Nerve Sheath Fenestration (ONSF): A decompressive procedure specifically to protect vision.

Prognosis

Permanent visual field defects occur in up to 17% of children, and reduced visual acuity in 10%. Therefore, rigorous monitoring of visual acuity and visual fields (perimetry) is essential during follow-up.