What is the most likely initial diagnosis for an elderly woman with left lower quadrant quadrantanopia, inability to correctly identify left-side sensation, and a recent history of fall and wrist fracture, despite being lucid and having intact proprioception?

Acute Ischemic Stroke Affecting the Right Parietal Lobe

The most likely initial diagnosis is an acute ischemic stroke affecting the right parietal lobe, given the combination of left lower quadrant quadrantanopia with left-sided sensory extinction (hemineglect). This constellation of findings—particularly the inability to identify left-side tactile stimulation during bilateral simultaneous stimulation despite preserved sensation when tested individually—is pathognomonic for a contralateral parietal lobe lesion 1.

Key Diagnostic Features Supporting Right Parietal Stroke

The sensory extinction phenomenon (hemineglect) is the critical localizing sign. When the patient could not correctly identify left-side sensation during simultaneous bilateral tactile stimulation, this indicates right parietal lobe involvement, as extinction/inattention is specifically assessed in stroke evaluation protocols and strongly suggests parietal pathology 2. This finding, combined with the visual field defect, makes parietal stroke the leading diagnosis.

Visual Field Defect Localization

• Left lower quadrantanopia most commonly localizes to the right parietal lobe (89% of cases have associated localizing signs like hemineglect) 1
• While occipital lobe lesions cause 76% of inferior quadrantanopias, they typically present as neurologically isolated findings without other signs 1
• The presence of sensory extinction essentially rules out an isolated occipital lesion 1

Fall Mechanism Explained by Stroke

The fall itself was likely caused by the acute stroke, not the other way around. The patient "bumped into a coffee table and then tripped"—this pattern of spatial navigation difficulty and impaired awareness of left-sided objects is classic for right parietal stroke with hemineglect 2. The wrist fracture occurred secondary to the neurological event.

Clinical Reasoning Algorithm

When evaluating quadrantanopia, follow this localization hierarchy:

1. Check for associated neurological signs (sensory deficits, neglect, language problems) 1
2. If other signs present → Parietal lobe lesion (89-100% of parietal lesions have associated findings) 1
3. If neurologically isolated → Occipital lobe lesion (76-83% of isolated quadrantanopias) 1
4. Superior quadrantanopia without other signs → Consider temporal lobe (13% of cases) 1

This patient clearly falls into category #2 with prominent sensory extinction, making right parietal stroke the diagnosis 1.

Immediate Management Priorities

Time-critical evaluation for thrombolytic therapy is essential. The patient presents within a potential treatment window, and IV tPA administered within 0-180 minutes of symptom onset significantly improves outcomes 2:

• Number needed to treat = 8.3 for minimal or no disability at 90 days 2
• 39% of tPA-treated patients achieve modified Rankin Scale 0-1 (no residual disability) versus 26% with placebo 2
• Despite 6% risk of symptomatic intracerebral hemorrhage, overall mortality is not increased (17% tPA vs 21% placebo) 2

Required Immediate Actions

• Obtain exact time of symptom onset (when did the fall occur?) to determine tPA eligibility 2
• Perform NIHSS scoring including the specific items already documented: visual fields (score 1 for quadrantanopia), extinction/inattention (score 1 for unilateral neglect) 2
• Emergency brain imaging (CT to exclude hemorrhage, followed by MRI for definitive stroke characterization) 2

Critical Pitfalls to Avoid

Do not attribute the fall solely to mechanical causes and miss the underlying stroke. The combination of spatial navigation errors (bumping into furniture) and fall in an elderly patient should immediately trigger stroke evaluation, especially when neurological deficits are found on examination 2.

Do not delay imaging because the patient appears "otherwise lucid." Preserved consciousness and proprioception do not exclude significant stroke—parietal strokes frequently spare alertness while causing profound sensory and spatial deficits 2, 1.

Do not assume the wrist injury is the primary problem. While the fracture requires orthopedic management, the stroke is the life-threatening emergency requiring immediate intervention within the therapeutic window 2.