Chapter 14-12: Infarction of the Pons or Cerebellum

TEXTBOOK PRESENTATION

Typically, the presenting symptoms are rapid onset of hemiparesis, sensory symptoms, or ataxia.

DISEASE HIGHLIGHTS

1. Etiology: Brainstem strokes may occur due to either lacunar infarction or nonlacunar mechanisms.

   1. Lacunar infarction

      1. Account for 15–26% of ischemic strokes

      2. Long-standing hypertension causes lipohyalinosis of the small penetrating vessels, which may thrombose and cause lacunar infarction.

      3. Commonly involves the pons; other common locations include the basal ganglia, internal capsule, and thalamus.

      4. Incidence in the black population is approximately twice that in the white population.

      5. Cortical signs (aphasia, agnosia, apraxia, and hemianopsia) are absent.

   2. Isolated cerebellar infarction is often due to nonlacunar mechanisms, including cardioembolism, large vessel atherosclerosis, and occasionally VAD.

      1. Large vessel atherosclerosis may cause stroke if there is either thrombosis or artery to artery downstream embolization.

      2. Identification of artery to artery embolization is important due to the much higher stroke recurrence rate in these patients compared with patients without such lesions (16% vs 1%).

   3. Hypertension, diabetes mellitus, smoking, dyslipidemia, atrial fibrillation, and valvular heart disease are important risk factors.

   4. 25% of these strokes occur in patients < 50 years of age in whom the leading cause is VAD. Such patients often lack traditional risk factors leading clinicians to underestimate the risk of stroke. (See VAD below.)

2. Complications: Deterioration in the first 3 days occurs in 10–20% of patients with cerebellar strokes.

   1. Occurs due to swelling, hemorrhage, and brainstem compression.

   2. Such patients may require emergent neurosurgical intervention.

   3. Missed diagnoses are associated with a marked increase risk of death.

   4. This is a must not miss diagnosis that requires a detailed neurologic evaluation, frequently accompanied by neuroimaging.

EVIDENCE-BASED DIAGNOSIS

1. > 34% of patient with cerebellar stroke are misdiagnosed. The most common misdiagnosis was vestibular neuritis.

2. Pontine/cerebellar strokes may be associated with vertigo, ipsilateral weakness, ataxia, dysarthria, and nystagmus. The dizziness may be described as vertigo, tilting, or swaying.

3. Certain symptoms are important clues that suggest cerebellar stroke when present but are insensitive and often absent.

   1. Headache

      1. Although insensitive (23–40% overall) headaches are an important clue to the diagnosis of cerebellar infarction

      2. A case series has shown that headaches were present in 13 of 15 patients in whom the diagnosis was missed.

   2. Other focal findings were also unusual (see Table 14-8)

   3. Furthermore, only 27% of patients with vertigo due to small brainstem infarctions had focal symptoms.

   4. Vertigo:

      1. It is estimated that 10–55% of patients with acute persistent vertigo have suffered a stroke.

      2. Vertigo was the presenting symptom in 23% of patients with cerebellar infarction.

      3. Similar to BPPV and vestibular neuritis, vertigo may be exacerbated by head motion.

         Vertigo exacerbated by motion is not pathognomonic of BPPV and should not exclude the consideration of other etiologies.

      4. The HINTS exam is highly accurate for the diagnosis of stroke and other CNS causes of central vertigo in patients with the acute vestibular syndrome (Table 14-5).

         1. Sensitivity, 96.8%; specificity, 98.5%

         2. LR+, 63.9; LR–, ...