The correct answer is B. The clinical manifestations in the scenario are consistent with fat embolism. This complication is frequently associated with fractures of long bones, but this 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 complications from 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 who have cardiac arrhythmias with thrombi in the right atrium or ventricle. Thromboemboli in the brain cause ischemia/ 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.
PEARL: Fat embolism is a clinical diagnosis. It usually presents with a history of trauma to long bones or pelvis (including orthopedic procedures). Symptomatic patients present with respiratory distress, neurologic impairment, and a petechial rash over the upper body. Petechial rash, present in only 20% of cases, is considered pathognomonic in the setting of long-bone trauma.
