A dilated pupil in a comatose patient caused by a tumor or subdural hematoma compressing the superficial pupillary fibers of CN III is known as which pupil?

A dilated pupil in a comatose patient caused by a tumor or subdural hematoma compressing the superficial pupillary fibers of CN III is known as which pupil?

• A. Hutchinson's Pupil
• B. Argyll Robertson Pupil
• C. Tonic Pupil
• D. Adie's Pupil

Answer: (A)

When a mass or subdural bleed raises intracranial pressure, it can push the temporal lobe (uncus) and compress the superficial parasympathetic fibers of the oculomotor nerve (CN III). Those fibers innervate the sphincter pupillae, so their loss causes the pupil to lose its constriction in light. The result is a unilateral, fixed, dilated pupil in a comatose patient—a classic sign of uncal herniation. This specific finding is known as Hutchinson's pupil. By contrast, Argyll Robertson pupils are small and irregular with light-near dissociation (seen in neurosyphilis), and tonic/Adie pupils are dilated with a poor light response due to postganglionic iris innervation problems, not acute mass effect.

When a mass or subdural bleed raises intracranial pressure, it can push the temporal lobe (uncus) and compress the superficial parasympathetic fibers of the oculomotor nerve (CN III). Those fibers innervate the sphincter pupillae, so their loss causes the pupil to lose its constriction in light. The result is a unilateral, fixed, dilated pupil in a comatose patient—a classic sign of uncal herniation. This specific finding is known as Hutchinson's pupil.

By contrast, Argyll Robertson pupils are small and irregular with light-near dissociation (seen in neurosyphilis), and tonic/Adie pupils are dilated with a poor light response due to postganglionic iris innervation problems, not acute mass effect.