Bilateral Medial Medullary Infarction with Distal Stenosis of Hypoplastic VA

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Bilateral Medial Medullary Infarction with Distal Stenosis of Hypoplastic Vertebral Artery: A Comprehensive Case Analysis

Bilateral medial medullary infarction (MMI) represents an exceptionally rare subtype of ischemic stroke, accounting for less than 1% of all cases. This condition is characterized by its distinct clinical and radiological features, often leading to severe neurological deficits. The present case report details a 54-year-old male patient who exhibited rapidly progressive tetraparesis and bulbar dysfunction, ultimately diagnosed with bilateral MMI secondary to atherosclerotic stenosis in a hypoplastic vertebral artery (VA). This analysis explores the clinical presentation, imaging findings, pathophysiological mechanisms, and therapeutic implications of this rare entity.

Clinical Presentation and Disease Progression

The patient, a 54-year-old man with a medical history of hypertension and diabetes, presented with sudden-onset dizziness in the morning, followed by somnolence in the afternoon. By 11 PM the same day, he developed mild left-sided weakness and slurred speech. Over the next 24 hours, his condition deteriorated rapidly, culminating in flaccid quadriplegia (muscle power 0/5 in all limbs), dysarthria, and bilateral Babinski signs. Notably, the neurological examination revealed preserved pupillary reflexes, normal eye movements, and an absence of nystagmus, tongue paralysis, or sensory disturbances. These findings localized the lesion to the bilateral medial medulla, sparing the dorsal columns and spinothalamic tracts.

Imaging Findings and Diagnostic Clues

Brain magnetic resonance imaging (MRI), performed one day after symptom onset, revealed subtle hyperintensity in the bilateral anteromedial medulla on axial T2-weighted imaging. Diffusion-weighted imaging (DWI) demonstrated a characteristic hyperintense “heart appearance” sign in the ventral medulla (Figure 1A), a pathognomonic radiological feature of bilateral MMI. Computed tomography angiography (CTA) further identified two critical vascular abnormalities: (1) hypoplasia of the left vertebral artery, evidenced by its significantly reduced caliber throughout the extracranial course compared to the contralateral side, and (2) atherosclerotic stenosis in the V4 segment of the left VA, distal to its hypoplastic segment (Figure 1B).

Pathophysiological Mechanisms

The pathogenesis of bilateral MMI in this case involves interplay between congenital vascular variation and acquired atherosclerotic disease. Vertebral artery hypoplasia (VAH), a congenital anatomical variant present in approximately 10% of the population, predisposes to posterior circulation ischemia by reducing collateral flow reserves. In this patient, the hypoplastic left VA likely compromised perfusion to the medullary branches, while the superimposed atherosclerotic stenosis in the V4 segment (proximal to the basilar artery) further exacerbated hemodynamic insufficiency.

Three mechanisms may explain bilateral MMI arising from unilateral VA pathology:

  1. Anatomic Variability of Medullary Perforators: Anomalous branching patterns may allow a single diseased VA to supply perforators to both sides of the medial medulla.
  2. Thrombus Propagation: Embolic material from the stenotic V4 segment could extend to the vertebrobasilar junction, occluding bilateral anterior spinal arteries or medial penetrating branches.
  3. Common Origin of Bilateral Anterior Spinal Arteries: If both anterior spinal arteries arise from the affected VA, stenosis could simultaneously compromise perfusion to bilateral medial medullary territories.

Clinical and Epidemiological Context

Bilateral MMI manifests with variable symptom complexes, typically including quadriplegia, sensory deficits, hypoglossal palsy, and respiratory failure. However, this case presented atypically with pure motor quadriplegia and bulbar dysfunction, underscoring the anatomical specificity of the infarct. The medial medulla houses corticospinal tracts, hypoglossal nuclei, and descending autonomic fibers, but sparing of the dorsal medulla (nucleus gracilis/cuneatus) accounted for the absence of sensory loss.

Systematic reviews indicate that large-artery atherosclerosis and small penetrating artery disease constitute the predominant etiologies for bilateral MMI. This case aligns with the former category, demonstrating how hypoplasia and atherosclerosis in a single VA can synergistically cause bilateral infarction. Notably, VAH-related strokes more commonly affect the posterior inferior cerebellar artery (PICA) territory or pons, making this medullary localization exceptionally rare.

Therapeutic Management and Prognosis

The patient received standard antiplatelet therapy (aspirin 100 mg/day) and high-intensity statin (atorvastatin 40 mg/day) for secondary stroke prevention. Respiratory compromise necessitated tracheotomy on hospital day two, reflecting the progression to bulbar dysfunction. Despite two weeks of intensive care, no motor recovery occurred (limb power remained 0/5). At three-month follow-up, the patient exhibited severe disability (modified Rankin Scale score 4), highlighting the grave prognosis associated with extensive bilateral medullary damage.

Diagnostic and Therapeutic Implications

This case emphasizes several critical considerations:

  1. Neuroimaging Correlation: The “heart appearance” sign on DWI is a hallmark of bilateral MMI, reflecting infarction of the pyramidal decussation and paramedian structures. Radiologists should recognize this pattern to expedite diagnosis.
  2. Vascular Evaluation: CTA or MR angiography is mandatory to identify VA hypoplasia and atherosclerotic lesions, even in patients without classical posterior circulation symptoms.
  3. Respiratory Monitoring: Early anticipation of respiratory failure is crucial, as 30%–40% of bilateral MMI cases require mechanical ventilation.

Conclusion

Bilateral medial medullary infarction remains a neurologically devastating stroke subtype, often resulting from the confluence of vascular anomalies and atherosclerotic disease. This case illustrates how hypoplastic VA anatomy, when combined with distal stenosis, can precipitate bilateral medullary ischemia through unique hemodynamic mechanisms. Clinicians must maintain high suspicion for posterior circulation pathology in patients with rapidly progressive quadriparesis, even in the absence of sensory or cranial nerve deficits. Early recognition of the “heart appearance” sign on DWI and aggressive management of respiratory complications may improve outcomes in this rare but critical condition.

doi.org/10.1097/CM9.0000000000000171

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