As you prepare for the USMLE® Level 1 (United States Medical Licensing Examination®) exam, you may want to know which questions are most often overlooked by test preparers. Check out this example from Kaplan Medical and read an expert statement on the answer. Also take a look at all the articles in this series.

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This month’s stumper

This month’s stumper

A 71-year-old man who works as a lawyer is rushed to the emergency room 20 minutes after being in a car accident. The physical exam reveals multiple cuts on the face and extremities, and bruises on the thorax. X-rays of the spine and chest are normal. The non-contrasting head CT shows some evidence of minor age-appropriate brain atrophy, but no evidence of bleeding.

After being admitted for overnight observation, he is discharged from the hospital. Three weeks later, his wife took him to the emergency room because of confusion. He does not orient himself to time or place and after three minutes he can only call up one of six objects.

Which of the following is most likely?

ON. Alzheimer’s disease.

BB Brain metastases.

C. Epidural hematoma.

DD Normal pressure hydrocephalus.

EE Subdural hematoma.

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The correct answer is EE

Kaplan Medical explains why

Kaplan Medical explains why

This is a classic history and presentation of a chronic or subacute subdural hematoma in which symptoms can appear several days or up to three weeks after a traumatic head injury.

The patient often had an initial hospitalization with a negative work-up and no evidence of abnormalities on serial CT scans of the head. However, the patient may experience deteriorating mental status, drowsiness, focal neurological deficits, seizures, etc., either gradually or abruptly, due to subdural accumulation of blood and subsequent compression of the brain.

The bleeding arises from the bridging veins of the meninges. Because the bleeding is under venous pressure (as opposed to the arterial pressure of an epidural hematoma), it may take more time for blood to accumulate before symptoms appear. The atrophy of the brain allows more space and movement in this area. Thus, trauma with a coup-contrecoup effect can cause trauma and shear of the bridging vessels. Abnormal hemostasis (e.g., thrombocytopenia, platelet dysfunction, overdose of anticoagulants) can also cause subdural bleeding.

A CT or MRI scan of the brain shows a semicircular, crescent-shaped opacity (blood) just below the skull that hits the brain tissue (see picture). The crescent shape reflects blood that crosses the skull suture lines (as opposed to an epidural hematoma that does not cross the suture lines).

On the other hand, acute subdural hematomas can occur within a few hours of a particularly severe injury due to widespread damage to the bridging veins. These cases are particularly devastating as up to 50% of patients are coma after an injury. It is much more difficult to distinguish this clinically from an epidural hematoma. However, when symptoms are present, a head CT typically shows a massive crescent-shaped hematoma.

Why the other answers are wrong

Why the other answers are wrong

Choice A: Alzheimer’s disease usually develops more slowly, typically over several years (although some cases can develop over a few months). In Alzheimer’s disease, cognitive deficits that affect memory, language, and executive function are early and profound, with motor and continence problems occurring later in the disease. MRI findings in this state are relatively unspecific with generalized cortical atrophy (particularly of the hippocampus).

Choice B: Brain metastases could very well be present, as described here; However, the patient often has constitutional symptoms of cancer such as fatigue and weight loss. For metastatic disease, head CT may or may not have a mass, although a mass large enough to show signs of compression would likely appear on imaging. This patient with recent trauma is far more likely to have a subdural hematoma.

Choice C: An epidural hematoma is unlikely in this patient as his symptoms developed over weeks rather than hours. Patients with epidural hematomas typically show symptoms much earlier (a few hours) because the bleeding originates from the middle meningeal artery, which is adjacent to the anterolateral (temporal) skull and is often injured by a fracture at this point. The high arterial pressure in combination with the limited drainage space leads to rapid compression of the brain and the production of symptoms.

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The classic representation for the epidural hematoma is a blow to the head causing an immediate loss of consciousness (from initial impact) with recovery and a temporary “clear period” followed by a decrease in consciousness. If left untreated, eventually coma and / or death (from brainstem compression). A CT or MRI scan shows a lenticular opacity within the skull, compressing the brain tissue. The space in which blood can collect is limited by side sutures into which the dura is inserted, giving them a lenticular (biconvex) appearance. This is in contrast to the crescent-shaped opacity of a subdural hematoma, as epidural bleeding does not cross the suture lines.

Choice D: Normal pressure hydrocephalus occurs in the elderly and is associated with the triad of urinary incontinence, recurrence of confusion, and gait disorders (“wet, crazy, and shaky”). Typically, gait disorders occur earlier in the course of the disease compared to Alzheimer’s. Unlike the scan in this patient, the CT shows dilated ventricles, but CSF studies usually show normal pressure (hence the name). Typically, patients have a history of meningitis, subarachnoid hemorrhage, or some other cause of damage to the arachnoid granulations that impair CSF absorption.

Tips to remember

Tips to remember

Subdural hematoma:

  • Usually traumatic and caused by rupture of the bridge veins.
  • Predisposing conditions: cerebral atrophy and abnormal hemostasis.
  • Slower venous bleeding may take longer to cause symptoms (i.e., subacute and chronic forms).
  • Creates a crescent shape when imaging (contrast-free CT is a first-line diagnostic method).
  • Features of presentation can include headache, drowsiness, focal neurological deficits, and sometimes dementia.

For more preparatory questions about USMLE steps 1, 2, and 3, see other posts in this series.