What are the clinical differences between Posterior Circulation Infarct (POCI) and Anterior Circulation Infarct (PACI)?

Clinical Differences Between POCI and PACI

Posterior circulation infarcts (POCI) and partial anterior circulation infarcts (PACI) differ substantially in their clinical presentation, with POCI showing more cranial nerve and cerebellar signs while PACI presents with more cortical deficits, though both share surprisingly high rates of common motor and sensory findings that make clinical differentiation unreliable without neuroimaging.

Clinical Presentation Patterns

Most Common Symptoms (Surprisingly Similar)

• Homolateral hemiplegia is the most frequent finding in both territories, occurring in 53.6% of POCI versus 74.9% of PACI patients 1
• Central facial/lingual palsy occurs in 40.7% of POCI versus 62.2% of PACI 1
• Hemisensory deficits show nearly identical frequencies: 36.4% in POCI versus 34.2% in PACI 1

Distinguishing Features of POCI

The following signs are highly specific for POCI (approaching 100% positive predictive value) but have extremely low sensitivity (1.3-4.0%), making them useful only when present 1:

• Horner's syndrome (4.0% in POCI vs 0% in PACI; PPV=100%) 1
• Crossed sensory deficits (3.0% vs 0%; PPV=100%) 1
• Crossed motor deficits (4.0% vs 0.1%; PPV=92.3%) 1
• Oculomotor nerve palsy (4.0% vs 0%; PPV=100%) 1
• Quadrantanopia (1.3% vs 0%; PPV=100%) 1
• Vestibulo-cerebellar signs are significantly more common in POCI 2
• Visual field defects occur more frequently in POCI 2
• Decreased consciousness is more prevalent in POCI 2

Distinguishing Features of PACI

• Hemisyndromes (combined motor, sensory, and visual field defects) are more common in PACI 2
• Dysarthria occurs more frequently in PACI 2
• Cognitive symptoms (aphasia, neglect) are more prevalent in PACI 2

Critical Clinical Pitfall

The symptoms traditionally considered "typical" of POCI occur far less often than expected, and relying on clinical neurological deficits alone to differentiate POCI from PACI leads to frequent mislocalization 1. Neuroimaging is essential for accurate diagnosis 1.

Stroke Severity and Assessment

• NIHSS scores underestimate severity in POCI because the scale emphasizes limb and speech impairments rather than cranial nerve lesions 3
• POCI patients present with lower NIHSS scores at admission compared to PACI 2
• Despite lower initial NIHSS, POCI patients may have worse 90-day functional outcomes (worse mRS distribution) compared to PACI 4

Etiological Differences

Similar Etiologies

• Small-artery occlusion is the most common etiology for both: 37.6% in POCI versus 37.1% in PACI 5

POCI-Specific Patterns

• Cardioembolism is significantly less common in POCI (5.4%) compared to PACI (13.3%; OR=0.373) 5
• Arterial dissection occurs more frequently in POCI 2
• Lacunar mechanisms are more common in POCI 2
• Intracranial arterial pathology is more prevalent in POCI 2
• Male gender confers greater risk for POCI (OR=1.392) 5
• Diabetes mellitus increases POCI risk more than PACI (OR=1.667) 5

PACI-Specific Patterns

• Cardioembolic strokes are more frequent in PACI 2
• Atrial fibrillation increases PACI risk (OR for POCI=0.530) 5
• Heart valve disease increases PACI risk (OR for POCI=0.433) 5

Natural History and Prognosis

PACI-Specific Outcomes

• Early recurrent stroke risk is more than twice as high in PACI compared to other stroke subtypes 6
• PACI patients have intermediate functional outcomes 6

POCI-Specific Outcomes

• Later recurrent stroke risk (after the early period, extending through the first year) is higher in POCI 6
• POCI has the best chance of good functional outcome among all stroke subtypes 6
• However, recent data suggests worse 90-day mRS distribution in POCI compared to PACI despite similar rates of recurrent vascular events 4
• Mortality rates are similar between POCI and PACI at 3 months 2

Acute Treatment Considerations

Imaging Characteristics

• POCI shows fewer early ischemic signs on admission CT compared to PACI 2
• Less overall arterial pathology is visible in POCI 2
• 24-hour recanalization rates are lower in POCI 2

Reperfusion Therapy

• IV thrombolysis rates are lower in POCI compared to PACI 2
• Endovascular recanalization is performed more frequently in POCI 2
• DAPT effectiveness and safety are similar between POCI and PACI in mild-to-moderate strokes (90-day ischemic event risk: 3.1% vs 2.9%) 4

Basilar Artery Occlusion (Severe POCI)

• EVT plus best medical treatment is preferred over medical treatment alone, particularly with NIHSS ≥10 3
• Successful recanalization is a strong predictor of survival 3
• Failure of recanalization is associated with high mortality 3

Practical Clinical Algorithm

1. Do not rely on clinical examination alone to distinguish POCI from PACI—obtain urgent neuroimaging 1
2. If classic "crossed" signs are present (crossed motor/sensory deficits, Horner's syndrome, oculomotor palsy), POCI is virtually certain 1
3. If only hemiplegia, facial palsy, or hemisensory loss is present, either territory is possible and imaging is mandatory 1
4. For secondary prevention planning: Consider that PACI has higher early recurrence risk requiring aggressive early intervention, while POCI has higher late recurrence risk requiring sustained prevention 6
5. For prognostication: POCI generally has better functional outcomes despite potentially worse mRS distribution in the short term 4, 6