A case of acute compressive optic neuropathy

British Journal of Neurosurgery, December 2010; 24(6): 705–707

SHORT REPORT

A case of acute compressive optic neuropathy secondary to aneurysmal bone cyst formation in fibrous dysplasia

Br J Neurosurg 2010.24:705-707. Downloaded from informahealthcare.com by The University of Manchester on 01/09/14. For personal use only.

STEPHEN P. MACNALLY1, REIKO ASHIDA1, TOBY J. WILLIAMS2, ANDREW T. KING1, BRIAN LEATHERBARROW3 & SCOTT A. RUTHERFORD1 1

Department of Neurosurgery, 2Department of Neuroradiology, Salford Royal Hospital, Manchester, UK, and 3Department of Opthalmic Surgery, Manchester Royal Eye Hospital, Manchester, UK Abstract We report a 19-year-old female with craniofacial fibrous dysplasia who had presented with rapidly progressive visual loss in her right eye secondary to aneurysmal bone cyst formation. Craniotomy with drainage and curettage of this bone cyst resulted in progressive improvement in visual acuity that returned to normal 5 months post-operatively.

Key words: Optic neuropathy, craniotomy, cyst, histology.

Introduction Fibrous dysplasia (FD) is a benign disease in which normal medullary bone is replaced by benign abnormal fibro-osseus tissue.1 It usually starts before the third decade and slowly progresses until *30 years of age. It is caused by post-zygotic somatic activating mutations in the signalling protein Gsa.2 FD may involve a single anatomical region (monostotic variant) or multiple regions (polyostotic variant) with this latter variant sometimes being part of the McCune-Albright syndrome (FD þ cafe´ au lait pigmentation and/or one of a number of hyperfunctioning endocrinopathies). Visual loss is the commonest neurological complication of FD affecting the skull and may occur acutely or chronically.3 Visual impairment in FD is most commonly due to optic canal stenosis or bone cyst formation, but it may also occur secondary to exophthalamos induced optic nerve traction, spontaneous haemorrhage and sinus mucocoele formation. Malignant transformation occurs in *0.5% of cases, which may be associated with bone cyst formation, and occurs more frequently in the polyostotic variant.1 Clinical details This patient had previously been diagnosed with craniofacial FD at 10 years of age following a cranial biopsy at another neurosurgical unit. She was followed up for 6 years and offered surgical intervention for cosmetic reasons, which she de-

clined, and was discharged with static disease. At 19 years, she subsequently visited another hospital with a 1-week history of progressive deterioration in visual acuity in her right eye along with headaches and dizziness. An examination noted obvious prominence of the right frontal bone, 4–5 mm of non-axial proptosis of the right eye with a corrected visual acuity of 6/24, a relative afferent pupillary defect and optic disc oedema. The left eye was normal. An ophthalmology opinion was sought and the patient received three doses of 500 mg methylprednisolone i.v. but her visual acuity progressively deteriorated over 3 days to only hand movements in the right eye. She was then referred to our department when her visual acuity had further deteriorated to only perception of light. A CT scan revealed FD affecting the right frontal, maxillary, sphenoid and ethmoid bones with a lucent area in the sphenoid bone medial to the right optic canal consistent with an aneurysmal bone cyst (ABC) (Fig. 1). This ABC was not present on old imaging performed some years previously at another unit. An MRI scan revealed this cyst to be compressing the right optic nerve. A right fronto-temporal craniotomy was performed urgently with extensive hyperostosis noted anterior to the coronal suture. The sphenoid wing was visualised extradurally and the dura was elevated allowing a frameless stereotactic-guided extradural approach to the region of the anterior clinoid process. This was facilitated by drilling the lateral part of the hyperostotic sphenoid ridge, and the cyst was then entered from its superior aspect (medial to the anterior

Correspondence: Stephen MacNally, Department of Neurosurgery, Salford Royal Hospital, Manchester M6 8HD, UK. E-mail: [email protected] Received for publication 13 December 2009. Accepted 4 June 2010. ISSN 0268-8697 print/ISSN 1360-046X online ª 2010 The Neurosurgical Foundation DOI: 10.3109/02688697.2010.500409


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FIG. 2. Post-operative axial CT scan showing partial decompression of the bone cyst medial to the optic canal. FIG. 1. Pre-operative axial CT scan showing changes consistent with fibrous dysplasia and a lucent area medial to the right optic canal indicating aneurysmal bone cyst formation.

clinoid and optic canal). Xanthochromic fluid and some fibrous and granular tissue was encountered within the cyst. Curettage of the bone cyst revealed much softer bone surrounding the cyst compared to the extremely hard bone of the sphenoid, frontal and temporal bones. The cyst contents were completely removed, along with the softer bone of the cyst wall, although limited curettage was performed laterally to avoid damage to the optic canal. Wide fenestration of the cyst was performed to allow drainage into the extradural space. A histopathology examination of temporal bone specimens revealed typical features of FD with the sphenoid cyst tissue showing changes compatible with secondary ABC formation. There were no malignant features in any of the specimens. The patient’s visual acuity progressively improved post-operatively from finger counting on day 1 to 6/ 24 on day 14, and to 6/6 at 5 months with a minimal temporal paracentral scotoma with this improvement maintained at 2 years follow-up. Post-operative CT scans revealed the sphenoid cystic cavity to have decreased in size and demonstrated the position of the bone flap relative to the hyperostotic bone (Figs. 2 and 3). Initial prognosis was guarded, but in the 2 years since surgery, there has been no involutional change within her FD and we are cautiously optimistic that her disease is not progressing. Discussion Cystic change may occur some years after the initial diagnosis of FD and is commonly associated with pain (probably secondary to elevated intracystic pressure), rapid enlargement of the FD lesion and/ or neurological signs depending on the location of the cyst.1 These cysts vary in histological appearance

FIG. 3. Post-op CT reconstruction showing the craniotomy site posterior to the hyperostotic right frontal bone.

and include simple bone cysts and ABCs with both types being composed of blood-filled cavities which are lined by a thick layer of fibrous tissue. It has been postulated that these ABCs arise from an intraosseous vascular defect that results in intramedullary haemorrhage. Visual failure most commonly occurs with ABCs located in the anterior clinoid region and steroids are an appropriate temporising measure in preparation for surgery when acute visual failure has occurred but are not a stand alone treatment in this situation.3 The visual outcome after ABC decompression varies with blindness, stabilisation and complete resolution all described in the few cases reported. There is a possibility of cyst recurrence and close follow-up is indicated. The other main cause of visual failure in FD is optic nerve encasement without cyst formation.2 Excess growth hormone production in patients with


Optic neuropathy in fibrous dysplasia FD is associated with an increased risk of optic nerve encasement and compressive optic neuropathy. However, the vast majority of optic nerves encased with FD do not have optic neuropathy and do not require prophylactic optic nerve decompression on the basis of diagnostic imaging alone. The importance of long-term follow-up of patients with craniofacial FD cannot be overstated. Regular visual field assessment is vital as it is commoner to develop gradual visual changes secondary to bony stenosis than acute visual failure as occurred in this case. Visual field assessments are more sensitive than CT scans in noting this gradual visual deterioration. However, it is still important to follow these patients with CT scans at maximum time intervals. The overall time interval of such follow-up is difficult to ascertain but should continue until the patient is *30 years of age, at which stage the risk of progressive bone changes and/or cyst formation falls significantly. An acute change in vision should be acted upon immediately with CT scanning usually sufficient to diagnose ABC formation. Systemic steroids are indicated while preparing for surgery.

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The use of image guidance was invaluable in this challenging case due to the distorted anatomy and extensive hyperostotic bone (Fig. 3). A histopathological examination of all specimens is vital as cystic changes may rarely be associated with malignant change. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

References 1. Diah E, Morris DE, Lo L, Chen Y. Cyst degeneration in craniofacial fibrous dysplasia: clinical presentation and management. J Neurosurg 2007;107:508. 2. Cutler CM, Lee JS, Butman JA, et al. Long-term outcome of optic nerve encasement and optic nerve decompression in patients with fibrous dysplasia: risk factors for blindness and safety of observation. Neurosurg 2006;59:1011–18. 3. Dumont AS, Boulos PT, Jane JA, Ellegala DB, Newman SA, Jane Snr JA. Cranioorbital fibrous dysplasia: with emphasis on visual impairment and current surgical management. Neurosurg Focus 2001;10:E6.