American Journal of Neuroradiology

Case of the Month

Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO

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October 2019

Next Case of the Month Coming November 5...

Idiopathic Intracranial Hypertension and Autosomal Dominant Osteopetrosis Type I

Background:
- Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri and benign intracranial hypertension, is a syndrome that typically presents symptoms secondary to increased CSF pressure and papilledema and classically, but not exclusively, affects middle-aged women with a BMI ≥30.
- Osteopetrosis is thought to be secondary to osteoclast dysfunction resulting in abnormal bone architecture, leading to an increased risk for bone fractures and aberrant bone thickening. There is an infantile autosomal recessive form and an adult autosomal dominant form.
Clinical Presentation:
- In IIH, patients may present with signs and symptoms of increased intracranial pressure, such as nausea, vomiting, visual changes, and headaches.
- In IIH, classically no focal neurologic deficits are detected, but some patients may exhibit unilateral or bilateral sixth nerve palsy.
- Autosomal dominant osteopetrosis has 2 subtypes.
  - Type I results in diffuse calvarial thickening with strong bones resistant to fracture. Patients with osteopetrosis of the skull can present with cranial nerve palsies, facial nerve pain, decreased visual acuity, and deafness.
  - Type II is more prone to fractures and involves the skull base in addition to involvement of the axial and appendicular skeleton.
Key Diagnostic Features:
- Diagnostic features of IIH on MRI include tortuosity of the optic nerves, partially empty sella turcica, enlarged Meckel’s cave, prominent arachnoid pits, venous sinus stenosis, and ≥25 cm of H2O with normal CSF composition.
- The classic diagnostic feature of osteopetrosis in the head and neck is diffuse calvarial thickening and increased bone density.
Differential Diagnoses:
- Chiari I malformation may share many similar imaging findings with IIH due to a similar pathogenesis (eg, intracranial hypertension).
- Intracranial mass and venous sinus thrombosis may present similarly to IIH with headaches, abducens nerve palsy, and other visual changes.
- The differential for osteopetrosis of the calvarium includes Paget disease of the bone, acromegaly, fibrous dysplasia, chronic anemias, and chronic antiepileptic medication. Patient history and additional bone findings will clench the diagnosis.
Treatment:
- Treatment of IIH includes serial lumbar punctures for interval decrease of CSF pressure and relief of symptoms, medical therapy with acetazolamide, and surgical intervention with placement of a lumboperitoneal shunt.
- Bone marrow transplant can be used to treat patients with severe osteopetrosis when disease severity leads to frequent fractures and neurologic sequelae.