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Question:

A 74-year-old man with metastatic lung cancer is brought to the emergency department due to sudden-onset severe headache, nausea, and vomiting.  The patient was diagnosed with squamous cell lung cancer 4 months ago and was found to have metastasis to the right frontal lobe of the brain.  He refused chemotherapy and radiation treatments and is receiving palliative care.  Blood pressure is 142/86 mm Hg, pulse is 100/min, and respirations are 20/min.  On examination, the patient is somnolent but wakes up to voice and follows instructions.  Urgent CT scan of the head reveals hemorrhage within the tumor, causing significant surrounding edema; the right cingulate gyrus is seen herniating beneath the falx cerebri.  Which of the following findings is most likely to be present in this patient given his neuroimaging results?

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Explanation:

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Clinical features of brain herniation

Herniation type

Common features

Subfalcine

  • Herniation of cingulate gyrus underneath falx cerebri
  • No pupillary involvement, consciousness often preserved
  • Contralateral leg weakness (ipsilateral ACA compression)

Uncal

  • Herniation of uncus (medial temporal lobe) under tentorium cerebelli
  • Ipsilateral dilated & fixed pupil (ipsilateral oculomotor nerve [CN III] compression)
  • Early: contralateral hemiparesis (ipsilateral cerebral peduncle compression)
  • Late: ipsilateral hemiparesis (contralateral cerebral peduncle compression)

Central

  • Caudal displacement of diencephalon & brainstem
  • Rupture of paramedian basilar artery branches
  • Bilateral midposition & fixed pupils (loss of sympathetic & parasympathetic innervation)
  • Decorticate (flexor) → decerebrate (extensor) posturing

Tonsillar

  • Herniation of cerebellar tonsils through foramen magnum
  • Coma, loss of CN reflexes, flaccid paralysis, respiratory arrest (brainstem compression)

ACA = anterior cerebral artery; CN = cranial nerve.

Brain herniation occurs when an acute increase in intracranial pressure (ICP) causes a portion of the brain to protrude through an opening in the dural folds or foramen magnum.  In this patient, mass effect from hemorrhage within the right frontal lobe metastasis is causing the cingulate gyrus, which is located at the medial aspect of the cerebral cortex just above the corpus callosum, to herniate beneath the falx cerebri (ie, subfalcine herniation).

Unlike in other herniation syndromes (eg, uncal, tonsillar), some consciousness is usually preserved in subfalcine herniation because there is no compression of brainstem wakefulness centers (eg, reticular activating system).  Initial presentation may be as subtle as a headache; however, signs of increased ICP (eg, nausea, vomiting, lethargy) are often present, as in this patient.  As it progresses, subfalcine herniation can cause ipsilateral anterior cerebral artery compression, leading to downstream ischemia and contralateral leg weakness.

(Choice A)  A dilated and fixed right pupil may occur in uncal herniation due to compression of the ipsilateral oculomotor nerve (CN III).  Uncal herniation involves herniation of the most medial portion of the temporal lobe (ie, uncus) beneath the tentorium cerebelli.

(Choice C)  Conjugate eye deviation is a classic finding in middle cerebral artery (MCA) stroke.  Resulting damage to the frontal eye field interrupts conjugate gaze, with the eyes directed toward the side of the lesion (eg, leftward gaze in left MCA stroke).

(Choice D)  Loss of gag and cough reflexes may be seen with brainstem (eg, medulla) compression or injury, as can occur with acute herniation of the cerebellar tonsils through the foramen magnum.

(Choice E)  Nonfluent/agrammatic speech (ie, expressive [motor] aphasia) is usually the result of injury to the Broca area, as can occur from a stroke involving the superior division of the dominant (typically left) middle cerebral artery.

Educational objective:
Subfalcine herniation occurs when the cingulate gyrus is displaced under the falx cerebri.  Subfalcine herniation may compress the ipsilateral anterior cerebral artery, resulting in ischemia and contralateral leg weakness.