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Show Isolated Sixth Nerve Palsy From Hemorrhage of a Pontine Cavernous Malformation Robert M. Mallery, MD, Joshua P. Klein, MD, PhD, Misha L. Pless, MD Abstract: A 32-year-old woman who developed binocular horizontal diplopia was found to have an isolated fascicular sixth nerve palsy secondary to hemorrhage of a cavern-ous malformation within the left pontine tegmentum. There was sparing of the paramedian pontine reticular formation and absence of a horizontal gaze palsy. The natural history of cavernous malformations and a mechanism by which hemorrhage of these vascular lesions may produce minimal neurologic signs, including isolated ocular motor cranial nerve palsies, is discussed. Magnetic resonance imaging (MRI) that includes susceptibility-weighted sequences leads to their accurate diagnosis. Journal of Neuro-Ophthalmology 2012;32:335-337 doi: 10.1097/WNO.0b013e31825e42ca © 2012 by North American Neuro-Ophthalmology Society Ahealthy 32-year-old woman awoke with binocular hor-izontal diplopia and a sensation of pressure in her head. On examination, there was a left esotropia measuring 20 prism diopters in primary gaze and limited abduction of the left eye. Ductions and torsional eye movements were other-wise intact, and the remainder of the neurologic examination was normal. Given her young age and lack of vascular risk factors, brain magnetic resonance imaging (MRI) was obtained that demonstrated a 5 · 5-mm2 lesion within FIG. 1. Brain magnetic resonance imaging (MRI) performed 4 days after onset of symptoms. (A) T1 sagittal scan shows a ring of hyperintensity within the inferior pons. (B) T1 axial postgadolinium scan shows no enhancement of the lesion. (C) Axial fluid-attenuated inversion recovery (FLAIR) scan reveals a rim of T2 hyperintensity (arrow) surrounding the lesion, consistent with vasogenic edema. (D) Susceptibility-weighted imaging shows hypointensity within the lesion, consistent with blood products. Department of Neurology (RMM, MLP), Massachusetts General Hos-pital, Boston, Massachusetts; and Department of Neurology (RMM, JPK), Brigham and Women's Hospital, Boston, Massachusetts. The authors report no conflicts of interest. Address correspondence to Misha L. Pless, MD, 15 Parkman Street, WACC Suite 835, Boston, MA 02114; E-mail: pless.misha@mgh. harvard.edu Mallery et al: J Neuro-Ophthalmol 2012; 32: 335-337 335 Photo Essay Section Editor: Timothy J. McCulley, MD Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. the left pontine tegmentum, consistent with a cavernous malformation (Fig. 1). The lesion was deemed inoperable, and her clinical deficit improved spontaneously over 6 months. Brain MRI at that time showed resolution of hem-orrhage and edema (Fig. 2). A lesion within the pontine tegmentum classically causes an ipsilateral, conjugate, horizontal gaze palsy because of either a failure of saccadic initiation by the excitatory burst neurons within the paramedian pontine reticular forma-tion or loss of their axonal connections to the ipsilateral sixth nerve nucleus. In contrast, our patient presented with an isolated abduction deficit of the left eye, presumably from involvement of the left sixth nerve fasciculus. The remarkable absence of neighborhood signs in this case provides evidence that hemorrhage of cavernous malforma-tions within eloquent areas of the brainstem may present with relatively minor neurologic deficits, including isolated ocular motor cranial nerve palsies. Cavernous hemangiomas are vascular malformations that occur in approximately 0.4%-0.8% of the general popula-tion and typically cause initial symptoms in the third or fourth decade (1-4). They are well-circumscribed lesions that may reach several centimeters in diameter and consist of thin-walled, sinusoidal-like blood vessels. The risk of hem-orrhage is estimated at 0.1%-3.1% per lesion per year, and the risk increases if there has been a previous hemorrhage (1). Their prevalence at various sites in the brain is pro-portional to brain volume, and the pons is thus a site of predilection in the brainstem accounting for approximately 62%-75% of brainstem cavernous malformations (2,4). The risk of hemorrhage from an infratentorial location has been reported to be 1.2-5.5 times greater than the risk from a cortical lesion (5). The fact that cavernous malformations do not contain internal neural tissue may explain why hemorrhage of these lesions can be asymptomatic or result in only minor neurologic impairment. Although cavernous malformations distort surrounding neural tracts, there is no interruption of connectivity or function. When hemorrhage occurs primar-ily within the lesion itself and spares the surrounding brain parenchyma, there may be minimal effect on adjacent neural structures. Detection of cavernous malformations has been facil-itated by the use of MRI and protocols that include susceptibility-weighted sequences. In our patient, a cavern-ous malformation with subacute hemorrhage appeared hyperintense on T1 and T2 sequences (Fig. 1). Cavernous malformations are distinguished from other vascular malformations by lack of enhancement with administration of contrast (Fig. 1B). Subacute hemorrhage is often FIG. 2. Brain magnetic resonance imaging performed 6 months after onset of symptoms. (A) T1 sagittal scan shows that most of the lesion appears isointense to brain. (B) T1 axial postgadolinium scan shows that the lesion is nonenhancing and contains an area of hypointensity (arrow). (C) Axial fluid-attenuated inversion recovery scan demonstrates resolution of abnormal T2 hyperintensity and a persistent rim of T2 hypointensity (arrow). (D) Susceptibility-weighted imaging reveals persistent hypointensity within the lesion, consistent with blood products. 336 Mallery et al: J Neuro-Ophthalmol 2012; 32: 335-337 Photo Essay Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. accompanied by surrounding edema (Fig. 1C). Susceptibil-ity- weighted sequences are highly sensitive for blood prod-ucts, demonstrating hypointensity in the area of the lesion (Fig. 1D). Chronically, with resolved hemorrhage, the lesion may appear isointense or hypointense on T1 sequences (Fig. 2A, B) with a peripheral rim of T2 hypointensity, consistent with hemosiderin (Fig. 2C). With recurrent hemorrhage leading to accumulation of blood products of varying ages, the lesion takes on the typical "popcorn" appearance of mixed signal intensity on TI and T2 sequences. Hypo-intensity on susceptibility-weighted imaging persists in the chronic phase because of hemosiderin deposition (Fig. 2D) or dystrophic calcification. Our case illustrates a good prognosis for neurologic recovery from a first-time hemorrhage. The patient's symptoms resolved over a 6-month period, suggesting remyelination of the sixth nerve fasciculus as hemorrhage and edema resolved. However, cavernous malformations carry a high risk for recurrent hemorrhage and must be con-sidered as a potential cause of an "idiopathic" ocular motor cranial nerve palsy. REFERENCES 1. Batra S, Lin D, Recinos PF, Zhang J, Rigamonti D. Cavernous malformations: natural history, diagnosis, and treatment. Nat Rev Neurol. 2009;5:659-670. 2. Curling OD Jr, Kelly DL Jr, Elster AD, Craven T. An analysis of the natural history of cavernous angiomas. J Neurosurg. 1991;75:702-708. 3. Fritschi J, Reulen J, Spetzler R, Zabramski J. Cavernous malformations of the brain stem. A review of 139 cases. Acta Neurochir (Wien). 1994;130:35-46. 4. Robinson JR, Awad IA, Little JR. Natural history of the cavernous angioma. J Neurosurg. 1991;75:709-714. 5. Flemming K, Link M, Christianson T, Brown R. Prospective hemorrhage risk of intracerebral cavernous malformations. Neurology. 2012;78:632-636. Mallery et al: J Neuro-Ophthalmol 2012; 32: 335-337 337 Photo Essay Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. |
