A 36-year-old man develops rapid mental status deterioration two days after sustaining a femoral fracture in a skiing accident. Physical examination shows multiple petechiae in the anterior chest and abdomen. On the third day, the patient lapses into coma and dies. Postmortem examination of the brain reveals numerous petechial hemorrhages in the corpus callosum and centrum semiovale. Which of the following is the most likely diagnosis?
A. Diffuse axonal injury
B. Fat embolism
C. Septic embolism
D. Systemic thromboembolism
E. Watershed infarction
Explanation: The correct answer is B. The clinical manifestations are consistent with fat embolism. This complication is frequent, following fractures of long bones, but is usually asymptomatic. Fat embolism mainly affects the lungs and the brain, and the clinical picture consists of dyspnea, tachycardia, and mental status changes. Only rarely, does this condition lead to death. In the lungs, fat emboli can be visualized histologically. In the brain, multifocal petechiae in the white matter represent the most common pathologic change.
Diffuse axonal injury (choice A) is one of the most common forms of traumatic brain injury. It involves the central white matter, especially the corpus callosum and cerebral peduncles. It is sometimes associated with small petechiae in these areas. The patient may develop coma a few hours to days after head trauma.
Septic embolism (choice C) results from septic emboli lodging in the terminal intraparenchymal arteries of the brain. It leads to multiple cortical infarcts, usually of the hemorrhagic type. The white matter is spared.
Systemic thromboembolism (choice D) is usually of cardiac origin—for example, in patients with cardiac arrhythmias with thrombi in the right atrium or ventricle. Thromboemboli in the brain cause hemorrhagic infarction in the cortex.
Watershed infarction (choice E) is often seen in patients suffering from acute hypotensive episodes, especially if the circle of Willis is already compromised by atherosclerotic change. The cortical regions at the border zone between different vascular territories (e.g., between the distribution of the anterior and middle cerebral arteries) undergo ischemic necrosis.