What is the next step in evaluating a healthy 22-year-old with left-sided numbness and a negative computed tomography (CT) head scan?

Next Steps for Left-Sided Numbness in a Healthy 22-Year-Old with Negative CT Head

MRI of the brain with and without contrast is the next appropriate imaging study for this patient, as CT has limited sensitivity for detecting subtle posterior fossa lesions, small cortical contusions, white matter lesions, and early ischemic changes that could explain persistent focal neurological deficits in a young patient. 1

Why CT Was Insufficient

• CT has poor sensitivity for subtle intracranial pathology that commonly presents with isolated sensory symptoms, particularly lesions adjacent to the skull base, small white matter abnormalities, and early ischemic stroke 1
• While CT is excellent for detecting acute hemorrhage and skull fractures requiring neurosurgical intervention, it frequently misses the pathology responsible for persistent focal neurological deficits like unilateral numbness 1
• MRI is significantly more sensitive than CT for detecting small cortical contusions, subdural hematomas near the calvarium, diffuse axonal injury, and white matter lesions 1

MRI Brain: The Appropriate Next Step

MRI brain with diffusion-weighted imaging (DWI) should be obtained to evaluate for:

• Acute ischemic stroke, which MRI with DWI can detect with much higher sensitivity than CT, particularly in young patients where stroke may present atypically 1
• Demyelinating disease (multiple sclerosis), which commonly presents with sensory symptoms in young adults and requires MRI for diagnosis 1
• Posterior fossa lesions including cerebellar or brainstem pathology that could affect sensory pathways 2
• Small mass lesions such as cerebellopontine angle tumors or other structural abnormalities 1

Contrast Administration

• Gadolinium contrast should be included to evaluate for enhancing lesions such as demyelinating plaques, tumors, or inflammatory processes 1
• The ACR guidelines support MRI as a second-line study when persistent neurological deficits remain unexplained after negative CT 1

Critical Clinical Context

This Is NOT a Trauma Case

• The provided evidence about mild traumatic brain injury 1, 3, 4, 5 is not applicable to this clinical scenario
• There is no mention of head trauma in the presentation
• Left-sided numbness in a healthy 22-year-old without trauma requires evaluation for stroke, demyelination, or mass lesion, not traumatic injury

Age-Specific Considerations

• At age 22, stroke is uncommon but not impossible, particularly with unrecognized risk factors (hypercoagulable states, cardiac abnormalities, arterial dissection) 1
• Demyelinating disease (MS) typically presents in this age group with focal neurological symptoms 1
• The differential diagnosis differs substantially from older patients where vascular disease predominates

Additional Workup to Consider Concurrently

While MRI is being arranged, the following should be evaluated:

• Detailed neurological examination focusing on cranial nerve function, sensory distribution (dermatomal vs. non-dermatomal), motor strength, coordination, and gait 2
• Vascular risk factor assessment including blood pressure, glucose, lipid panel, and consideration of hypercoagulable workup if stroke is suspected 1
• Cervical spine imaging may be warranted if the sensory deficit follows a dermatomal pattern suggesting radiculopathy rather than central pathology 1

Common Pitfalls to Avoid

• Do not assume a negative CT rules out significant pathology in a patient with persistent focal neurological deficits 1, 6
• Do not delay MRI while pursuing extensive laboratory workup; imaging should be obtained promptly to guide further evaluation 1
• Do not dismiss symptoms as functional without completing appropriate neuroimaging, particularly in young patients where serious pathology may present atypically 6
• Do not order MRA/CTA initially unless there is specific clinical suspicion for vascular pathology; start with brain MRI with contrast 1

Timing and Urgency

• MRI should be obtained urgently (within 24-48 hours) given the presence of unexplained focal neurological deficit 1
• If acute stroke is suspected based on sudden onset or rapid progression, emergent MRI with DWI is indicated 1
• The patient should be counseled to return immediately for worsening symptoms, new deficits, or development of weakness, vision changes, or speech difficulties 3