Uchino Akira
Department of Radiology, Saitama Sekishinkai Hospital.
No Shinkei Geka. 2021 Mar;49(2):278-283. doi: 10.11477/mf.1436204389.
Both fat and air have lower attenuation than water on CT images. Excluding ruptured dermoid cysts, a majority of intracranial fats have no clinical significance. In contrast, intracranial air sometimes indicates serious conditions. If CT attenuation of the lesion is apparently lower than that of the orbital fat, it can be regarded as an air bubble. T1-weighted MRI is useful for differentiating fat from air. Air in the subarachnoid space, called pneumocephalus, is a significant sign of serious head injury. In such cases, there may be cerebrospinal fluid leakage, and the risk of meningitis. Iatrogenic pneumocephalus is also observed, including lumbar puncture. Air in the artery is indicative of air embolism, which is a serious condition. It is caused by trauma and iatrogenic procedures. Both, right-to-left shunt in the heart and pulmonary arteriovenous fistula are risk factors for air embolism. Small air bubbles rapidly disappear from the arterial lumen. On the other hand, air in the dural sinuses is iatrogenic but usually asymptomatic. According to anatomical characteristics, air from the left hand easily migrates into the dural sinuses via the left internal jugular vein.
在CT图像上，脂肪和空气的衰减都低于水。除破裂的皮样囊肿外，大多数颅内脂肪并无临床意义。相比之下，颅内积气有时提示严重病情。如果病变的CT衰减明显低于眶内脂肪，则可视为气泡。T1加权磁共振成像有助于区分脂肪和空气。蛛网膜下腔积气，称为气颅，是严重头部损伤的重要体征。在这种情况下，可能存在脑脊液漏和脑膜炎风险。医源性气颅也有发现，包括腰椎穿刺。动脉内积气提示空气栓塞，这是一种严重情况。它由外伤和医源性操作引起。心脏右向左分流和肺动静脉瘘都是空气栓塞的危险因素。小气泡会迅速从动脉管腔消失。另一方面，硬脑膜窦内积气是医源性的，但通常无症状。根据解剖学特点，来自左手的空气容易通过左颈内静脉进入硬脑膜窦。
