Teaching NeuroImage: Convergence spasm associated with midbrain compression by cerebral aneurysm
Konrad P. Weber, MD,
Matthew J. Thurtell, MBBS and
G. Michael Halmagyi, MD
From the Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia.
Address correspondence and reprint requests to Dr. G. Michael Halmagyi, Department of Neurology, Royal Prince Alfred Hospital, Missenden Road, Camperdown NSW 2050, Australia michael{at}icn.usyd.edu.au
A 72-year-old woman presented with intermittent diplopia. Shehad a history of vascular disease, but no history of strokeor psychiatric disturbance. On examination, she developed convergencespasm with associated miosis following fixation on near targetsand during horizontal smooth pursuit (video, figure 1). Thespasms were terminated with a blink. She had no ptosis, hereye movements were normal in range, and her pupils were equalin size with normal reactions to light. Neurologic examinationwas otherwise unremarkable. Five years prior to her currentpresentation, a left-sided terminal carotid artery aneurysmhad been incidentally detected. The aneurysm gradually expandedto a diameter of 2.4 cm and compressed the midbrain (figure 2).The intermittent diplopia had developed in the months followingendovascular coiling of the aneurysm.
Figure 1 Infrared video stills and search coil recording of convergence spasm
(A–D) Convergence spasm precipitated by fixation on a near target and released after a blink (video, A). (A) During fixation on a distant target, the patient has mid-range pupils. (B) During fixation on a near target, the patient converges and has miotic pupils. (C) After the near target is removed, convergence is maintained. The pupils remain miotic, which helps to differentiate from bilateral sixth nerve palsies. (D) After a blink, the patient is able to re-fixate on the distant target and the pupils return to mid-range diameter. (E) Binocular search coil recording during sinusoidal horizontal smooth pursuit, in which there is a period of convergence spasm that is released by a blink (video, B). (F) The vergence angle progressively increases up to 50° during the period of convergence spasm (gray triangle).
Figure 2 T2-weighted axial MRI demonstrating progressive compression of the midbrain by an expanding aneurysm (arrowheads) arising from the terminal left carotid artery
(A) MRI 5 years prior to onset of symptoms. (B) MRI at the time of presentation with convergence spasm (after endovascular coiling of the aneurysm).
Convergence spasm is characterized by the inappropriate appearanceof the near triad, which consists of convergence, miosis, andaccommodation.1 Most patients are young and the cause is psychiatric;a focal lesion is rarely found.1 Since the neural substratefor the near triad is located in the midbrain, convergence spasmcould occur with a midbrain lesion. In our patient, isolatedconvergence spasm may have been a manifestation of midbraincompression. Thus, in patients presenting with convergence spasm,the presence of other focal neurologic signs or the absenceof psychiatric history, especially in the elderly, should promptneuroimaging. Furthermore, it is important not to mistake convergencespasm for bilateral sixth nerve palsies; miosis on attemptedlateral gaze is diagnostic of convergence spasm.2
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