Idiopathic Hypertrophic Pachymeningitis

Specific Imaging Findings Idiopathic hypertrophic pachymeningitis (IHP) presents with isolated dural thickening, which may be focal or extend over large portions of the intracranial dura mater, most commonly along the falx and tentorium. The thickened dura is hyperdense on CT and demonstrates peripheral enhancement on post-contrast images. MRI is the imaging modality of choice and it shows very low T2 signal intensity of the thickened dura with peripheral high T2 signal and contrast enhancement. The central pachymeningeal layer does not enhance, which is responsible for the characteristic triple layer appearance on post-contrast T1WI. The thickened dura is isointense on pre-contrast T1WI, sometimes with a central dark stripe. Spinal involvement may occur either with cranial IHP or as an isolated finding. Nodular masses may sometimes be encountered, while associated cranial hyperostosis is rarely present. Secondary brain edema, venous congestion, cavernous sinus thrombosis, hydrocephalus, and intracranial hemorrhages may sometimes be found. Pertinent Clinical Information The most common presenting symptoms of intracranial IHP are chronic daily headaches and cranial nerve palsies, followed by cerebellar dysfunction and seizures. Laboratory findings include mild elevation of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). CSF studies usually show aseptic inflammatory changes. Left untreated, the clinical course is usually marked by severe headaches, progressive neurologic deterioration, and visual loss. High-dose corticosteroid therapy results in improved symptoms and shrinkage of the lesions and methotrexate is an effective therapeutical option. Surgical decompression may provide symptomatic relief.