A 46-year-old male with a history of an uncorrected right-to-left cardiac shunt is evaluat… — USMLE Step 2 CK

A 46-year-old male with a history of an uncorrected right-to-left cardiac shunt is evaluated in the neurology unit for a progressively worsening, severe global headache over the past week. This morning, he developed new-onset weakness in his left arm and leg. His temperature is $38.6^\circ\text{C}$ ( $101.5^\circ\text{F}$ ), blood pressure is $145/90\text{ mm Hg}$ , and heart rate is $88\text{/min}$ . Neurologic examination reveals $3/5$ motor strength in the left upper and lower extremities and a left homonymous hemianopia. Fundoscopic examination shows bilateral optic disc swelling with blurred margins. A contrast-enhanced MRI of the brain demonstrates a $3.8\text{-cm}$ solitary ring-enhancing lesion with a necrotic core in the right frontoparietal lobe, surrounded by substantial vasogenic edema and a $7\text{-mm}$ midline shift. Which of the following is the most appropriate next step in management?

Stereotactic aspiration of the lesionAnswer
B
Lumbar puncture for cerebrospinal fluid analysis
C
Initiation of intravenous empiric antibiotics alone
D
Craniotomy for en bloc resection of the lesion
E
Intravenous dexamethasone and serial imaging in 4 weeks

Answer

Stereotactic aspiration of the lesion

The correct answer is stereotactic aspiration of the lesion. This patient's clinical presentation (fever, headache, focal neurologic deficits) and imaging findings (ring-enhancing lesion with a necrotic core and surrounding edema) in the setting of a right-to-left cardiac shunt are highly characteristic of a bacterial brain abscess. The standard of care for a brain abscess larger than 2.5 cm, or one causing significant mass effect (as evidenced by a 7-mm midline shift), is prompt stereotactic aspiration. This neurosurgical procedure is both diagnostic and therapeutic; it provides a microbial tissue sample to guide targeted antibiotic therapy and immediately relieves intracranial pressure by reducing the volume of the mass.

Step-by-Step Solution

Identify the primary diagnosis based on clinical and imaging findings

The patient has a large (3.8 cm) bacterial brain abscess with mass effect and midline shift, likely seeded via his uncorrected right-to-left cardiac shunt.

Establishing the correct pathology (abscess rather than primary tumor) is necessary to determine the appropriate neurosurgical and medical intervention.

Evaluate indications for surgical intervention

Brain abscesses larger than 2.5 cm or those causing significant mass effect (e.g., 7-mm midline shift) meet the criteria for surgical drainage.

Medical management alone is insufficient for large lesions and risks progressive neurologic decline and herniation.

Select the most appropriate neurosurgical technique

Stereotactic aspiration is chosen as the definitive initial step.

It successfully relieves intracranial pressure, provides a tissue sample for gram stain and culture, and minimizes morbidity compared to open craniotomy.

Key Concept

Management of Brain Abscesses > 2.5 cm

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