A 45-year-old, previously healthy man is brought to the emergency department due to acute-onset headache. The pain began 30 minutes ago when the patient was using the bathroom and is severe, generalized, and constant. He is also nauseated and progressively lethargic. The patient takes no medications. Temperature is 37.2 C (99 F), blood pressure is 150/90 mm Hg, pulse is 98/min, and respirations are 18/min. On physical examination, the patient appears somnolent and keeps his eyes closed. When he is instructed to open his eyes, there is obvious right-sided ptosis, and the right pupil is larger than the left. Which of the following is the most likely diagnosis?
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This patient's sudden onset of severe headache with an associated oculomotor nerve palsy and somnolence is highly suggestive of subarachnoid hemorrhage (SAH) due to a ruptured saccular aneurysm. In addition to acute-onset, severe headache, patients with SAH commonly have vomiting, photophobia, neck stiffness, and lethargy. Neurologic deficits are sometimes present at the time of presentation.
The arterial tree at the base of the brain is in proximity to many cranial nerve (CN) origins; therefore, certain isolated cranial nerve palsies can be a sign of a compressing aneurysm in a specific location.
Oculomotor nerve (CN III) palsy can involve pupillary dilation resulting from loss of parasympathetic innervation, as well as possible ptosis and down and out eye positioning due to loss of somatic innervation. Full or partial oculomotor nerve palsy suggests an enlarging or ruptured aneurysm of the adjacent posterior communicating artery.
In a similar manner, compression of the optic nerve (CN II) by an aneurysm of the internal carotid or anterior communicating artery can cause unilateral vision loss or bitemporal hemianopsia.
Less commonly, a trochlear nerve (CN IV) or abducens nerve (CN VI) palsy can result from an aneurysm affecting the superior cerebellar or anterior inferior cerebellar artery, respectively.
Blood from the ruptured aneurysm can irritate the nerve tract, which may worsen the focal neurologic finding. Management of a patient with sudden-onset, severe headache and signs of a cranial nerve palsy should include noncontrast CT scan of the head to evaluate for SAH and possibly angiography to evaluate for an enlarging aneurysm with impending rupture.
(Choice A) Carotid artery dissection typically presents with unilateral headache and ipsilateral Horner syndrome from interruption of sympathetic fibers along the internal carotid artery. However, carotid dissection would cause ptosis and pupillary constriction, not ptosis and dilation (from oculomotor dysfunction) on the right side, as seen in this patient.
(Choice B) Cavernous sinus thrombosis generally presents with fever, headache, and periorbital swelling. In addition, there is usually palsy of CN III, CN IV, and CN VI (all 3 nerves) resulting in an extensive ophthalmoplegia.
(Choice C) Cluster headache usually involves severe unilateral headache and ipsilateral signs of parasympathetic hyperactivity. Ptosis is common, but pupillary constriction (rather than dilation) would be expected.
(Choice D) Lateral medullary syndrome (Wallenberg syndrome) results from a stroke affecting the vertebral artery or posterior inferior cerebellar artery. Patients have contralateral sensory deficits of the extremities, ipsilateral sensory deficits of the face, and possible Horner syndrome.
Educational objective:
Isolated cranial nerve palsies can indicate a ruptured or enlarging saccular aneurysm with active or impending subarachnoid hemorrhage. Isolated oculomotor nerve palsy can indicate an aneurysm of the posterior communicating artery.