激しい頭痛で発症し，特徴的な神経放射線学的所見を呈したspontaneous intracranial hypotensionの2例

Spontaneous intracranial hypotension with severe headache and typical neuroradiological findings:report of two cases

I．はじめに

　腰椎穿刺などの医源性により頭蓋内圧が低下し，postural headacheを引き起こすことは良く知られているが，明らかな外因なしに頭蓋内圧低下をきたす病態も存在し，spontaneous intracranial hypotension（SIH）と呼ばれている．SIHは稀な病態であるが，最近posturalheadacheの原因として重視され，MRIでの髄膜の特徴的所見も報告されている^{5,8,11,13,14,20,28,31,32,35）}．今回，くも膜下出血と見誤るような激しい頭痛で発症し，経過中に硬膜下血腫を合併した症例と，頭痛で発症しMRIにて特徴的所見を呈した症例の2例のSIHを経験したので，本病態の臨床所見，および神経放射線学的特徴の文献的考察を加え報告する．

Intracranial hypotension causes the postural head-ache that sometimes follows lumbar puncture. When postural headache and associated symptoms occur after lumbar puncture,the diagnosis is usually obvious. However,similar symptoms may occur after minor trauma or without an obvious precipitating cause (spontaneous intracranial hypotension: SIH). SIH is rare, but is now increasingly recognized as a cause of postural headache. We encountered two cases of SIH showing typical neuroradiological findings.

Case 1 is a 47-year-old man who was admitted with severe frontalgia. CT scan revealed vague visualization of bilateral Sylvian fissures and slit ventricles. Spinal fluid pressure was 6cm H₂O in the lateral recumbent position. Cerebrospinal fluid (CSF) showed slight lym-phocytic pleocytosis. We treated him as having viral meningitis. His headache improved gradually and he was discharged 2 weeks later with slight occipitalgia. One week after discharge, he complained of severe headache again and plain CT showed bilateral subdural hematoma. The subdural hematoma in both sides was evacuated and his headache improved after the opera-tion. Follow-up CT scans two months later showed nor-malization of ventricle size and cisterns.

Case 2 is a 52-year-old woman who was admitted with severe occipitalgia. CT scan on admission showed slit ventricles and the disappearance of the suprasellar cistern and the Sylvian fissure. Spinal fluid pressure was 3cm H₂O. Gd-enhanced MRI showed remarkable meningeal enhancement and effacement of the optic chiasm suggesting brain sagging. Her headache im-proved 2 weeks later after strict bed rest and oral pain relief drugs. The follow-up MRI showed disappearance of abnormal meningeal enhancement and normalization of optic chiasma effacement.

SIH is one of the important differential diagnoses of patients complaining of postural headache. Meningeal enhancement of gadolinium-enhanced MRI is an impor-tant finding to diagnose SIH. We have to consider SIH when diagnosing postural headache.