Bored Review: Vascular 1 - Brainstem Syndromes and Vascular Neuroanatomy

Clinical Midbrain and Medullary Syndromes

• Cloud Syndrome (Claude Syndrome):

  • Characterized by femoral ataxia and third nerve ($3^{rd}$ nerve) palsy.

  • Localization concerns the midbrain, specifically affecting the area where the oculomotor nerve fibers and superior cerebellar peduncle fibers exit.

  • Clinical triad: Ipsilateral oculomotor nerve palsy, contralateral cerebellar ataxia, and sensory changes.

• Benedikt Syndrome:

  • Involves a lesion in the midbrain tegmentum.

  • Clinical features: Ipsilateral oculomotor ($3^{rd}$ nerve) palsy and contralateral movement disorders, such as ataxia, tremor (often a rubral or "wing-beating" tremor), or choreoathetosis due to involvement of the red nucleus and substantia nigra.

• Medial Medullary Syndrome (Dejerine Syndrome):

  • Clinical Presentation Case Study: A $60$-year-old patient presented to the ER with left-sided weakness, decreased proprioception, and right-sided tongue weakness.

  • Clinical Components:

    1. Ipsilateral Tongue Weakness: Due to involvement of the hypoglossal nerve ($CN\,XII$) or its nucleus. The tongue fibers run medially.

    2. Contralateral Hemiplegia/Hemiparesis: Due to involvement of the ventral pyramidal tract (corticospinal fibers).

    3. Contralateral Loss of Proprioception and Vibration: Due to involvement of the medial lemniscus.

  • Arterial Supply: Primarily the Anterior Spinal Artery (ASA).

  • Localization: Medial aspect of the medulla.

Neuro-Ophthalmology and Gaze Preferences

• PPRF (Paramedian Pontine Reticular Formation) Lesions:

  • The PPRF is the horizontal gaze center for the ipsilateral side.

  • Activation of the PPRF stimulates the ipsilateral abducens nucleus, which activates the ipsilateral lateral rectus.

  • Lesion Dynamics: If the right PPRF is affected by a stroke, the individual cannot look to the right. The eyes will deviate to the contralateral side (the left) due to the unopposed effect of the intact left PPRF.

  • Rule of Thumb: In brainstem lesions involving the PPRF, the gaze preference is contralateral to the side of the lesion (the eyes "look away" from the lesion and toward the weakness if hemiparesis is present).

• Frontal Eye Field (FEF) Lesions:

  • In supratentorial lesions (e.g., MCA stroke), the patient's eyes deviate toward the side of the lesion (ipsilateral gaze preference) and away from the hemiparesis.

• Persistent Gaze Preference Case Study:

  • An elderly diabetic, hypertensive female presented with sudden onset persistent left gaze preference that could not be overcome.

  • This indicates a brainstem lesion rather than a cortical one, as cortical gaze preferences typically can be overcome with the oculocephalic maneuver.

Basal Ganglia and Thalamic Vascular Supply

• Head of the Caudate Nucleus:

  • Vascular Supply: Primarily supplied by the Recurrent Artery of Heubner (a branch of the Anterior Cerebral Artery, $ACA$).

  • Infarction Features: Typically involves the head of the caudate and the adjacent anterior limb of the internal capsule. Clinically, this can result in weakness involving the face and arm (corticospinal tract involvement) and cognitive/behavioral changes.

• Thalamus Vascular Anatomy:

  • Paramedian Arteries: Supply the dorsomedial nucleus of the thalamus. Obstruction (Artery of Percheron) can cause bilateral medial thalamic infarctions.

  • Thalamogeniculate Arteries: Supply the ventral posterior nuclei (VPL and VPM). Infarction here typically causes pure sensory loss.

  • Anterior Choroidal Artery: Supplies the lateral geniculate body, the posterior limb of the internal capsule, and sometimes the ventral anterior nucleus.

  • Clinical Pearls: The Artery of Percheron is a common anatomical variant where a single arterial trunk supplies both medial thalami and the rostral midbrain. Infarction presents with acute onset loss of consciousness (due to involving the Reticular Activating System), ophthalmoplegia, or memory impairment.

Cranial Nerve Palsies and Vascular Compression

• Oculomotor Nerve ($3^{rd}$ Nerve) Palsy and Aneurysms:

  • Clinical Presentation: "Down and out" eye position, ptosis, and mydriasis (dilated pupil).

  • Vascular Culprit: An aneurysm of the Posterior Communicating Artery (BCom).

  • Differential Diagnosis: Pupil-sparing $3^{rd}$ nerve palsy is often microvascular (diabetes), whereas pupil-involved palsy is highly suspicious for compressive aneurysm.

  • Distinction from Horner Syndrome: Horner involves ptosis, myosis (constricted pupil), and anhidrosis (lack of sweating), localized to the sympathetic pathway (superior cervical ganglion or lateral brainstem).

• Internal Carotid Artery (ICA) Dissection:

  • Unique Presentation: A patient post-trauma (RTA) presenting with ptosis, myosis, and ipsilateral tongue deviation.

  • Mechanism: The hypoglossal nerve ($CN\,XII$) passes horizontally close to the internal carotid artery. An ICA dissection or associated pseudoaneurysm can compress the nerve locally at the subapical space.

Lateral Brainstem Syndromes (PICA vs. AICA)

• Lateral Medullary Syndrome (Wallenberg Syndrome):

  • Artery: Posterior Inferior Cerebellar Artery (PICA).

  • Clinical Signs: Vertigo, nausea, vomiting, gait instability, ipsilateral Horner syndrome, ipsilateral limb ataxia, and contralateral loss of pain/temperature in the limbs and trunk.

• Lateral Pontine Syndrome:

  • Artery: Anterior Inferior Cerebellar Artery (AICA).

  • Key Distinguishing Feature: Presence of unilateral hearing loss and tinnitus (due to involvement of the labyrinthine artery or vestibular/cochlear nerve at the cerebellopontine angle).

  • Commonalities with PICA: Both feature ataxia, dysarthria, and Horner syndrome.

Anterior Choroidal Artery and Lacunar Syndromes

• Anterior Choroidal Artery Syndrome:

  • Clinical Triad: Contralateral hemiparesis, contralateral hemianesthesia, and a specific visual field defect.

  • Visual Field Defect: Often causes a sectoranopia or a defect where the horizontal meridian is spared. This helps distinguish it from PCA strokes or optic radiation lesions.

  • Case Study: $45$-year-old male, non-diabetic/hypertensive, with right-sided weakness and sensory loss without aphasia. If the visual field shows horizontal sparing, the culprit is the anterior choroidal artery.

• Lacunar Syndromes:

  • Pure Motor Stroke: Usually localized to the posterior limb of the internal capsule or the basis pontis.

  • Pure Sensory Stroke: Localized to the VPL/VPM nuclei of the thalamus.

  • Ataxia-Clumsy Hand Syndrome: Often localized to the basis pontis (paramedian branches).

Language and Cortical Syndromes

• Aphasia Localization:

  • Wernicke's Area: Posterior superior temporal gyrus. Involved in comprehension.

  • Broca's Area: Inferior frontal gyrus. Involved in motor production of speech.

  • Transcortical Motor Aphasia: SMA (Supplementary Motor Area) or frontal regions near Broca's.

  • Transcortical Sensory Aphasia: Localization typically includes the angular gyrus or regions surrounding Wernicke's.

  • Conduction Aphasia: Arcuate fasciculus. Characterized by impaired repetition but intact comprehension.

• Occipital Lobe and PCA Syndromes:

  • Alexia Without Agraphia: Occurs with a lesion in the left occipital lobe and the splenium of the corpus callosum. The patient can write but cannot read what they have written because visual information from the intact right occipital lobe cannot reach the language centers in the left hemisphere.

  • Anton Syndrome (Cortical Blindness): Bilateral occipital lobe infarctions. The patient is functionally blind but denies it (anosognosia), often confabulating visual descriptions.

• Locked-in Syndrome:

  • Localization: Ventral pons (bilateral basis pontis).

  • Clinical Features: Complete paralysis of all voluntary muscles except for vertical eye movements and blinking (mediated by the midbrain). Consciousness is preserved.

Questions & Discussion

• Question: Where is the localization of Cloud Syndrome?

  • Answer: It involves the midbrain tegmentum, specifically where the third nerve and cerebellar fibers interact.

• Question: What is the artery supply to the head of the caudate?

  • Answer: Recurrent artery of Heubner.

• Question: Why does the patient with ICA dissection have tongue deviation?

  • Answer: The dissection or an adventitial aneurysm compresses the hypoglossal nerve locally as it passes near the ICA.

• Question: How do we distinguish between PICA and AICA syndromes in the exam?

  • Answer: Look for hearing loss or tinnitus; if present, it points toward AICA. Both have Wallenberg-like signs (Horner's, ataxia, sensory loss).

• Question: What is the visual field hallmark of a lesion in the anterior choroidal artery?

  • Answer: A large field defect with preservation of the horizontal meridian.