Management of esotropia: hypotropia in neurofibromatosis type 1 – simulating myopic strabismus fixus
- Mayank Jain and
- Ramesh Kekunnaya
- Jasti V Ramanamma Children's Eye Care Center, Child Sight Institute, LV Prasad Eye Institute, Hyderabad, Telangana, India
- Correspondence to Dr Ramesh Kekunnaya; drrk123@gmail.com
Abstract
A 28-year-old man presented with a progressive inward deviation of the left eye in the last 4 years. Examination revealed −3 abduction and elevation deficit in the left eye with 50 prism diopters (PD) esotropia and 12 PD of hypotropia. The patient had multiple fibromas on the forearms with pulsatile globe and was diagnosed as neurofibromatosis type 1. Myopic strabismus fixus was suspected. MRI revealed left temporal lobe herniation through a dysplastic sphenoid wing, compressing the posterior half of the superior rectus and lateral rectus muscles, resulting in an esotropia-hypotropia complex. Surgical treatment involved suture myopexy (Yokoyama’s technique) of the left superior rectus and lateral rectus muscles with a 6.5 mm left medial rectus recession. Two months postoperatively, the patient had minimal residual esotropia and hypotropia. MRI orbits should always be performed in high myopes with strabismus to assess extraocular muscle pathways.
Background
Neurofibromatosis type 1 is an autosomal dominant disorder caused by mutations in the NF1 gene. Ocular manifestations include ptosis, iris hamartoma, glaucoma and optic nerve glioma. Strabismus, if present, is usually associated with optic nerve glioma, orbitofacial neurofibromatosis or sphenoid bone dysplasia. A pulsatile globe is also associated with sphenoid bone dysplasia. Esotropia-hypotropia complex in the presence of high myopia with limitations of ocular rotations is commonly observed in myopic strabismus fixus. However, there are rare case reports of esotropia and hypotropia in a patient with neurofibromatosis type 1 simulating myopic strabismus fixus.
Case presentation
A 28-year-old male presented with a progressive inward deviation of the left eye for 4 years. Best-corrected visual acuity was 0.0 logMAR in the right eye with refractive error of −10.00 dioptre sphere (DS)/−1.75 dioptre cylinder (DC) × 170° and 0.4 LogMAR in the left eye with refractive error of −8.50 DS/−3.50 DC × 180° in the left eye. Near vision was 0.0 LogMAR in both eyes with normal colour vision screened on Ishihara pseudoisochromatic plates. There was no relative afferent pupillary defect. The anterior segment and posterior segment examinations were unremarkable. On systemic examination, the patient had multiple fibromas on the forehand (figure 1) and a previous CT scan demonstrated left sphenoid bone dysplasia. There was no family history of neurofibromatosis and no iris Lisch nodules were present. The patient was diagnosed with neurofibromatosis type 1. As the patient wanted refractive surgery for spectacle removal, he underwent Implantable Collamer lens implantation in both eyes. The unaided visual acuity, then, was 0.0 logMAR in the right eye and 0.3 logMAR improving to 0.1 logMAR with −1DC in the left eye. After 2 months, strabismus evaluation was done and 50 prism diopters (PD) esotropia and 12 PD of hypotropia in the left eye were present. There was −3 abduction and elevation limitation in the left eye as shown in figure 2. Childhood photos were reviewed in which no strabismus was present. The globe was pulsatile on the left side as shown in the video (video 1). There were no complaints of diplopia, pain or other neurological and systemic symptoms.
Multiple fibromas (arrows) on the forearm of the patient.
Preoperative composite nine-gaze picture showing esotropia-hypotropia in primary position. Abduction and elevation limitation (arrows) can be observed.
Differential diagnosis
Strabismus in a case of neurofibromatosis type 1 is often associated with optic pathway glioma. As the patient had acquired esotropia and hypotropia with limited ocular rotations in presence of high myopia, myopic strabismus fixus was one of the differential diagnosis.
Investigations
Axial length was measured to be 27.69 mm in the right eye and 27.66 mm in the left eye. MRI of orbit was performed to study the pathways of extraocular muscles. We found the temporal cerebral lobe herniating into the left orbit through the dysplastic sphenoid wing. The brain parenchyma was compressing on the posterior aspect of superior and lateral rectus muscle (figure 3), causing esotropia-hypotropia complex. No evidence of optic pathway glioma or orbital neurofibroma was observed.
MRI orbit T2W axial and coronal section demonstrating the temporal lobe herniation (arrows) into the left orbit.
Treatment
No intervention was suggested from the neurosurgeon and oculoplastic surgeon, and with due clearance from all, the patient was planned for surgical correction of strabismus. Intraoperatively, forced duction test (FDT) was performed and medial rectus in the left eye was 2+tight. Nasalisation of the posterior pathway of the superior rectus muscle and inferiorisation of the posterior pathway of lateral rectus muscle was noticed. Suture loop myopexy (Yokoyama’s technique) of the superior and lateral rectus muscle was performed along with medial rectus recession of 6.5 mm in the left eye.
Outcome and follow-up
At 2-month postoperative follow-up, the patient had small residual esotropia of 12 PD and 6 PD of hypotropia in the left eye. Abduction and elevation limitation improved to −2 in the left eye as shown in figure 4.
Postoperative composite nine-gaze picture showing improvement in primary position deviation. Improvement in abduction and elevation limitation (arrows) can be observed as well.
Discussion
Neurofibromatosis is an autosomal dominant inherited disorder and 50% of the cases are known to occur sporadically without any family history. Sphenoid bone dysplasia is a progressive condition that presents in 4%–11% of the patients with this condition.1 The deficient greater wing of sphenoid leads to frontotemporal lobe herniation into the orbit resulting in pulsatile exophthalmos due to direct transmission of the pulsations from the brain to the globe of the eye. Strabismus in neurofibromatosis type 1 is mostly associated with optic pathway glioma (27%–29%) and orbitofacial neurofibromatosis (71%).2–4
Myopic strabismus fixus is characterised by esotropia and hypotropia with limitation of abduction and elevation in highly myopic eyes. There is superotemporal herniation of the enlarged globe causing nasal displacement of the superior rectus and inferior displacement of the lateral rectus.5
Lee et al described in their article, two patients of neurofibromatosis type 1 with large esotropia and hypotropia.6 However, their neuroimaging and the description of ocular motility was not mentioned. One case of true myopic strabismus fixus in a patient with neurofibromatosis was reported by Matsuura et al.7 Their patient had a high axial length of 32.2 mm in the right and 33 mm in the left eye. However, orbital neurofibroma was the aetiology behind strabismus fixus in this case.
Our patient had esotropia and hypotropia, with high myopia and typical abduction and elevation limitation, as seen in myopic strabismus fixus. However, the axial length was less than that of typically seen in patients of myopic strabismus fixus.8–10 On MRI, there was no superotemporal herniation of the globe but the muscle pathways were shifted due to herniation of the temporal lobe into the orbit. The finding was confirmed intraoperatively as well.
The treatment of sphenoid bone dysplasia has been successfully described by the placement of titanium mesh in scattered case reports.11–14 As the vision was not endangered, repair of the bony defect was not advised in our patient. Loop myopexy (Yokoyama’s technique) was performed to normalise the pathological pathway of the superior and lateral rectus. Medial rectus recession was added, as the FDT was tight for the medial rectus. Loop myopexy is an established technique for strabismus correction in myopic strabismus fixus.15 This technique worked in our case, as the extraocular muscle pathways were shifted due to brain parenchymal herniation, rather than the true strabismus fixus.
Learning points
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Strabismus in a patient with neurofibromatosis type 1 can be due to brain tissue herniating through sphenoid bone dysplasia without causing proptosis.
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MRI orbit without contrast should always be performed in cases of strabismus in high myopes to look for extraocular muscle pathways.
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Esotropia-hypotropia complex with limited ocular rotation in high myopes can occur in cases other than myopic strabismus fixus.
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Surgical treatment in such cases still should be directed at normalising the extraocular muscle pathways.
Footnotes
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Contributors RK took care of the patient from preoperative workup to postoperative care. The patient was operated under the care of RK. MJ designed the concept for case report. MJ was involved in collection of data, drafting the manuscript of the case report and ensuring all patient details and images to be collected along with proper consent from the patients. RK and MJ revised the manuscript and maintained the standards of the manuscript as per BMJ protocols. The final manuscript was approved by both authors, that is, RK and MJ. All authors are responsible for the integrity and accuracy of the data provided.
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Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
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Competing interests None declared.
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Patient consent for publication Obtained.
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Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.
References
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