Pediatric cranial nerve palsies have many etiologies, including neoplasm, trauma, infection, and metabolic insult. One example of metabolic insult to a cranial nerve is cerebral vascular compromise. Only a fraction of these presumed perinatal ischemic stroke cases present acutely at birth. To our knowledge, this is the first published case of unilateral abducens nerve palsy following perinatal stroke of the middle cerebral artery.
A male infant first presented to the pediatric neurology service at 8 months of age because of non-use of his right arm (with right hand balled in a fist), which his mother first noticed at 5 months of age. The prenatal course was complicated by preeclampsia diagnosed at 38 weeks. He was delivered vaginally under epidural anesthesia at 38 weeks with a birth weight of 5 pounds 13 ounces. Developmental milestones and review of systems were normal, except for the noted right-sided weakness.
On examination, a right hemiparesis was found that affected the right upper extremity more than the right lower extremity. No ocular-related abnormalities were documented by pediatric neurology. The patient was prescribed physical and occupational therapy. A magnetic resonance imaging (MRI) of the brain without contrast was ordered, which demonstrated cystic encephalomalacia in the left middle cerebral artery distribution with subtle asymmetric volume loss of the left facial colliculus (Figure 1).
Brain magnetic resonance imaging without contrast: (A) axial T2, (B) axial T2 flair, (C) coronal T2 flair, and (D) axial T2. Cystic encephalomalacia in the left middle cerebral artery territory, with associated ex vacuo dilatation of the left lateral ventricle. Patent basal cisterns. No mass lesions. Foci of hemosiderin deposition within the bilateral caudothalamic grooves and the right cerebellar hemisphere representing stigma of prior germinal matrix hemorrhage. Subtle asymmetric volume loss of the left facial colliculus adjacent to the left abducens nucleus.
At approximately 12 months of age, the mother noticed esotropia in the left eye and sought care with a comprehensive ophthalmologist. Examination confirmed left eye esotropia. He was prescribed +1.50 diopter sphere spectacles and started patching the right eye 2 hours per day for treatment of amblyopia. After 4 months of this regimen, he was referred to our tertiary care practice for strabismus evaluation and amblyopia management.
On our examination, Teller acuity with correction was found to be 6.5 cycles per centimeter (cy/cm) in the right eye and 4.8 cy/cm in the left eye. Fixation was central, steady, and maintained in the right eye, but central, steady, and unmaintained in the left eye. No afferent pupillary defect or anisocoria was noted. Ocular motility examination revealed a 35-prism diopter (PD) left eye esotropia in primary gaze at near and distance by Krimsky test with spectacle correction in place (Figure 2). The deviation remained unchanged at near without spectacle correction. The patient demonstrated full motility in the right eye and a −2 abduction deficit in the left eye, which was confirmed by doll's head maneuver. Penlight examination showed a normal anterior segment, and the posterior segment was found to be normal by indirect ophthalmoscopy. Cycloplegic refraction did not reveal significant refractive error in either eye. The patient was diagnosed as having left eye esotropia secondary to a left abducens nerve palsy and strabismic amblyopia in the left eye. A recess-resect procedure was recommended in the left eye. Spectacle correction was believed to be unnecessary, but patching in the right eye was maintained for 2 to 3 hours per day. A preoperative appointment was obtained, and examination was stable.
Preoperative photographs showing (A) primary gaze and (B) left gaze demonstrating a −2 abduction deficit.
He underwent left medial rectus recession of 5.5 mm and left lateral rectus resection of 7 mm. Forced ductions were negative at the time of surgery. His postoperative course was uncomplicated. At postoperative week 8, visual acuity was 9.8 cy/cm in the right eye and 4.8 cy/cm in the left eye. Motility was full in both eyes, and alignment was orthotropic in primary gaze by Hirschberg testing (Figure 3). Due to lack of patient cooperation, right gaze preoperative and left gaze postoperative photographs were unable to be obtained. Patching of the right eye 2 to 3 hours per day was continued for amblyopia treatment.
Postoperative primary gaze.
At 10 months after surgery, each eye was found to have improved visual acuity to 6.5 cy/cm, full motility, and fixation preference central, steady, and maintained. A 2 PD esophoria and 2 PD right hyperphoria was noted in primary gaze by prism alternate cover testing. Patching was discontinued. At 15 months after surgery, primary gaze by prism alternate cover testing revealed a 4 PD esophoria (small angle in left gaze with essentially no action of lateral rectus) and 2 PD right hyperphoria.
The patient continues to follow up with our service and pediatric neurology, physical therapy, and occupational therapy. No other neurologic sequelae have manifested.
Our patient's history, examination, and diagnostic tests are consistent with abducens nerve palsy. Despite the history of onset of the esotropia at 12 months of age, there was no accommodative component and no family history of strabismus to suggest accommodative or infantile esotropia as the etiology. The diagnosis was likely delayed by focus of the family and medical providers on the workup and treatment of the hemiparesis. The preoperative negative forced ductions and limited abduction in the left eye pointed toward abducens palsy as the most likely etiology.
The abducens nerve has the longest subarachnoid course of all of the cranial nerves, making it susceptible to compromise.1–3 Neoplasms, particularly compressive posterior fossa tumors and trauma, are among the most common etiologies of pediatric abducens nerve palsies and are caused by physical damage to the nerve.4 Metabolic insult to the abducens nerve can be secondary to central nervous system infection and, likely the case of our patient, vascular insufficiency.5
Although the incidence of perinatal stroke is estimated at approximately 1 in 4,000 live births, only a fraction present acutely at birth.6–8 Our patient's neurological findings are most consistent with presumed perinatal ischemic stroke.9,10 The volume loss of the left cerebral peduncle and left ventral pons along with the subtle asymmetry of the left facial colliculus implicate perinatal stroke as the cause of our patient's abducens palsy due to the location of the abducens' nucleus at the dorsal pontine tegmentum.11 The etiology of our patient's abducens palsy could also be due to the same ischemic process that caused the stroke, which has multiple predisposing factors, including low birth weight, elevated intracranial pressure associated with the birth process, and pre-eclampsia-related microvascular events in the setting of pregnancy/childbirth's prothrombotic state.6,8,12–14 Ultimately, the ophthalmologic management of the abducens palsy entails addressing neurological sequelae in a timely manner, treating the esotropia and strabismic amblyopia to optimize visual system development.
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