History: HIV-positive woman with severe headache, nausea, vomiting, and fever.
（HIV阳性妇女伴有严重头痛、恶心、呕吐和发烧。）
正确答案：弓形虫病
Toxoplasmosis of the CNS
Toxoplasmosis is the most common opportunistic CNS infection in patient's with AIDS (about 10% of AIDS patient's will develop this infection). The routes of transmission include ingestion of the tachyzoites (ingestion of uncooked meats) or oocysts (ingestion of feces-contaminated food), transplacental, transfusions, and organ transplants. More than 50% of the adult population in the US have antibodies to Toxoplasma. Acute toxoplasmosis in an immunocompromised patient usually occurs through the reactivation of a latent infection. The most common areas affected within the brain include the basal ganglia and the cortical medullary junctions. These lesions are usually associated with a moderate amount of edema and mass effect.（弓形虫病是艾滋病患者最常见的机会性中枢神经系统感染（约有10%的艾滋病患者会感染这种疾病）。传播途径包括弓形虫速殖子（未煮熟的肉类摄入）或卵囊（粪便污染的食物的摄入）、胎盘、输血、器官移植。美国成年人口中有超过50%的人有弓形虫抗体。免疫低下患者的急性弓形虫通常是通过潜伏感染再次发生。大脑内最常见的区域包括基底节区和皮髓交界区。这些病变通常伴有中度水肿和占位效应。）
Toxoplasmosis lesions tend to occur in the basal ganglia and cortical medullary junctions.Toxoplasmosis on a CT scan typically appears as a single or multiple ring-enhancing lesions with a moderate amount of peripheral edema.
On T1-weighted images, the lesions are hypointense relative to graymatter. On T2-weighted images , the lesions are hyperintense ,or occasionally isointense to hypointense. Surrounding edema is usually seen. Nodular or ring enhancement can be seen in approximately 70% of patients following intravenous injection of gadolinium.（弓形体病往往发生在基底节和皮髓交界区，CT上弓形虫通常表现为单个或多个环形强化病变，并伴有中等程度的周围水肿。T1加权像病灶相对于灰质呈低信号。在T2加权像呈高信号或偶尔呈中等偏低信号，通常可见周围水肿。静脉注射钆剂后约70%的患者可见结节状或环状强化。）
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