| OCR Text |
Show PHOTO ESSAY Superior Oblique Myokymia Caused by Vascular Compression Masato Hashimoto, MD, Kenji Ohtsuka, MD, Yasuo Suzuki, MD, Yoshihiro Minamida, MD, and Kiyohiro Houkin, MD FIG. 1. A, B: Serial axial plane magnetic resonance images ( 0.40- mm thick) using the FIESTA technique display the proximal cisternal segment of the left trochlear nerve { arrows) and a vessel lying on the root exit zone of the left trochlear nerve { arrowheads). C, D: The corresponding contrast SPGR images confirm the presence of an arterial branch { arrowheads) at the level of the trochlear nerve exit. Departments of Ophthalmology ( MH, KO, YS) and Neurosurgery ( YM, KH), Sapporo Medical University, School of Medicine, Sapporo, Hokkaido, Japan. Address correspondence to Dr. Masato Hashimoto, MD, Department of Ophthalmology, Sapporo Medical University School of Medicine, S- l, W- 16, Chuo- Ku, Sapporo 060, Japan, E- mail: mashoyu5@ beige. plala. or. jp Abstract: A 49- year- old man had left superior oblique myokymia for eight years. Magnetic resonance images with enhanced spoiled gradient recalled acquisition in the steady state ( SPGR) and flow imaging using steady acquisition ( FIESTA) disclosed a branch of the superior cerebellar artery lying on the root exit zone of the left trochlear nerve. J Neuro- Ophthalmol, Vol. 24, No. 3, 2004 237 JNeuro- Ophthalmol, Vol. 24, No. 3, 2004 Hashimoto et al FIG. 2. Photograph at surgery exposes the exit zone of the left trochlear nerve on the dorsal surface of the brain stem. ( The top of the picture is dorsal and the bottom is ventral.) A: A dorsal branch of the superior cerebellar artery { white arrows) compresses the trochlear nerve ( black arrow) at its root exit zone. Note that the trochlear nerve bulges because of this compression. B: The arterial branch has been pushed aside. C: Small pads of Teflon have been placed between the trochlear nerve and the vessel to separate these structures. Posterior fossa craniotomy confirmed the imaging findings. A Teflon pad was placed between the compressing artery and the trochlear nerve. The patient's superior oblique myokymia has completely resolved with a one- year follow- up. Only one such case has been previously reported. This is the first report to display the imaging findings. ( JNeuro- Ophthalmol 2004; 24: 237- 239) A49- year- old man presented with an intermittent " fluttering" sensation OS lasting for several seconds per episode and occurring repeatedly for eight years. Slit- lamp examination showed intermittent intorsional microtremor OS, diagnosed as left superior oblique myokymia. Conventional magnetic resonance imaging of his brain showed no abnormalities. Medical treatments such as carbamaze-pine and baclofen provided only short- term relief. His symptoms gradually worsened, disabling him from his job as a truck driver. To evaluate the brain stem in more detail, we used special magnetic resonance imaging sequences using enhanced spoiled gradient recalled acquisition in the steady state ( SPGR) and flow imaging using steady acquisition ( PIESTA). These sequences yield high- resolution images of very small structures surrounded by cerebrospinal fluid and very small vessels ( 1). Thin- slice ( 0.4 mm) sections showed the proximal cisternal segment of the left trochlear nerve at its root exit zone with a branch of the superior cerebellar artery lying on top of it ( Pig. 1). The patient elected to have a neurosurgical exploration of his left trochlear nerve. The root exit zone of the left trochlear nerve was exposed via a retrosigmoid approach. On the dorsal surface of the brain stem, a dorsal branch of the superior cerebellar artery was found to be compressing the trochlear nerve ( Fig. 2A). The arterial branch was pushed aside ( Fig. 2B) and small pads of Teflon were placed between the nerve and vessels ( Fig. 2C). When the patient awakened after surgery, his superior oblique myokymia was gone and has not recurred during a one- year follow- up. Immediately after surgery, the patient had a mild left trochlear nerve palsy that resolved completely in three months. Superior oblique myokymia, as termed by Hoyt and Keane ( 2) in 1970, is an acquired abnormality of superior oblique muscle innervation causing episodic torsional oscillation of an eye. In 1983, Bringewald ( 3) postulated that it resulted from vascular compression of the trochlear nerve. However, there has been only one reported case of compression of the trochlear nerve by vessels ( 4,5). Samii et al ( 4) and Scharwey and Samii ( 5) described a patient who had superior oblique myokymia for 17 years. The interposition of a Teflon pad between the trochlear nerve and a compressing artery and vein at the nerve's exit from the midbrain led to a remission lasting for a follow- up of 22 months. Their patient also experienced temporary ( five-month) ipsilateral trochlear nerve palsy. The surgical photograph of that case is similar to ours. Our patient differs in two ways from the previously reported case ( 4,5). First, we were able to identify by visualization at surgery that a branch of the superior cerebellar artery was the vessel compressing the trochlear nerve. Second, we were able to show the corresponding imaging abnormalities. Pathophysiologically, vascular compression syndromes such as hemifacial spasms or trigeminal neuralgia are hypothesized to develop because the junctional area between central and peripheral myelin is particularly vulnerable to continued pulsatile pressure. This pressure is believed to result in focal demyelination and in a short-circuiting of efferent nerve impulses. Fraher ( 6) observed 238 © 2004 Lippincott Williams & Wilkins Superior Oblique Myokymia by Vascular Compression JNeuro- Ophthalmol, Vol. 24, No. 3, 2004 histopathologically that the transitional zone between central and peripheral myelin in the trochlear nerve lies at its root exit zone. In our patient, an artery compressed the trochlear nerve at this transitional zone. REFERENCES 1. Yousry I, Dieterich M, Naidich TP, et al. Superior oblique myokymia: magnetic resonance imaging support for the neurovascular compression hypothesis. Ann Neurol 2002; 51: 361- 8. 2. Hoyt WF, Keane JR. Superior oblique myokymia: report and discussion on five case of benign intermittent uniocular microtremor. Arch Ophthalmol 1970; 84: 461- 7. 3. BringewaldPR. Superiorobliquemyokymia.^ 4rc/! A'eMro/ 1983; 40: 526. 4. Samii M, Rosahl SK, Carvalho GA, Krizizok T. Microvascular decompression for superior oblique myokymia: first experience. Case report. JNeurosurg 1998; 89: 1020- 4. 5. Scharwey K, Krzizok T, Samii M, et al. Remission of superior oblique myokymia after microvascular decompression. Ophthalmo-logica 2000; 214: 426- 8. 6. Fraher JP, Smiddy PF, O'Sullivan VR. The central- peripheral transitional regions of cranial nerves. Trochlear and abducent nerves. J Anat 1988; 161 T15- 123. 239 |
