Ординатура / Офтальмология / Английские материалы / Surgical Atlas of Orbital Diseases_Mallajosyula_2009

include ipsilateral episcleral hemangiomas, glaucomas and diffuse choroidal hemangioma and homonymous hemianopia.

Diffuse choroidal hemangioma gives a characteristic 'tomato-catsup' fundus.20 Imaging modalities like CT and MRI are used. CT scan may show 'tramline markings' of cerebral calcification.

Management includes the use of Erbium laser for naevus flammeus, external beam radiotherapy for diffuse choroidal hemangiomas and medical control of intraocular pressure followed by a combined trabeculotomy-trabeculectomy for glaucoma.21

Wyburn-Mason Syndrome: This is a rare A-V malformation of retina, optic nerve head and posterior fossa involving a direct communication between arteries and veins without the intervening capillary bed. Orbits are occasionally involved with ipsilateral portwine pigmented naevi over the trigeminal course.1 CT scans may show enlarged optic canal and bony orbit with a poorly defined enhancing mass.22

Klippel-Trenaunay Syndrome: This rare syndrome encompasses cutaneous hemangiomas, venous varicosities and bony and soft tissue hypertrophy of usually a single limb. Rarely is the orbit involved with vascular anomalies.23

SHUNTS

Carotid-Cavernous Fistula

As obvious from the name, it is an abnormal communication between the carotid artery and the cavernous sinus. The blood in the cavernous sinus becomes arterialized thereby raising the venous pressure and at the same time the arterial perfusion suffers. The fistula can be classified as 'direct or indirect', 'high flow or low flow ' and 'spontaneous or traumatic'. Barrow standardized the classification in 1985.24

Trauma is the most common cause of direct or type A fistulas usually seen in basal skull fractures. Indirect or type C, D, E, are due to congenital anomalies or spontaneous rupture of the artery

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Barrow's types of carotid-cavernous fistulas24

secondary to aneurysm, atherosclerosis and severe hypertension.

Clinical features include classical triad of conjunctival chemosis, pulsatile proptosis and bruit. Bruit is best heard as a flushing noise with the bell of the stethoscope, reduced by ipsilateral carotid compression in the neck. Other features include ptosis; increased intraocular pressure due to elevated episcleral pressure;25 anterior segment ischemia hallmarked by corneal edema, ischemic pseudoiritis, rubeosis iridis and cataract; ophthalmoplegia, most frequently affecting the 6th cranial nerve due to its intracavernous location; diplopia Fundus examination reveals dilated veins, optic disc edema and intraretinal hemorrhages.

Imaging modalities used are CT scan, MRI and angiography. CT scan shows enlarged superior ophthalmic vein, enlarged extraocular muscles and enlargement of the cavernous sinus.26 The definite test in selective internal or external carotid angiography which will demonstrate the fistula and its hemodynamics.

Carotid cavernous fistulas are managed by interventional radiologists.Usually these patients are first seen by an ophthalmologist/orbital surgeon who makes the diagnosis and refers to interventional radiologist for management. Management indications include secondary glaucomas, ophthalmoplegia, severe proptosis and intolerable bruit.27 Balloon/ coils or surgical occlusion of the fistula is recommended for the Type A. Balloon/coil can be introduced either by an arterial or a venous route.

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Type B and C can be treated with selective embolization of a single feeder vessel whereas Type D requires embolization of all the multiple feeder channels. Various complications of interventional radiology like vascular perforations, hemorrhage and permanent neurological deficit have been reported.28

New Growths

New growths can be further subdivided into 'Hamartomas' and 'Neoplasms'. The hamartomas are exemplified by cavernous hemangiomas whereas the neoplasms include 'hemangiopericytoma', 'Angiosarcoma', 'Kaposi Sarcoma', 'angiomyomas', etc.1

Capillary Hemangioma

Capillary hemangiomas are hamartomas characterized by growth of blood vessels along with proliferation of endothelium. These are common benign primary tumors of the orbit in children. It usually presents in the first or second week after birth and enlarges during the first year of life, after which they begin to involute. About 70% regress by 7 years of age.

Clinical presentation are in the form of strawberry naevus when the hemangioma involves the lid. Involvement of the conjunctiva is important from diagnostic point of view. Within the orbit anterior and superior quadrant of the orbit is a favoured site. Orbital lesions may present with a progressive non-pulsatile proptosis, which may increase following straining and crying.29 Capillary hemangiomas have important systemic implications like high output failure, 'Kasabach-Meritt Syndrome' (Anemia + thrombocytopenia + low coagulant factors)30 and 'Maffuci Syndrome' (Hemangiomas + enchondromatosis).

Imaging modalities used include CT scan, MRI and angiography.

CT scans demonstrates moderately well defined lesion with finger like projections that may be present in any orbital space. There is a moderate to intense enhancement on contrast. Gadolinium enhanced T1 wieghted images with fat suppression shows diffuse homogenous or heterogenous enhancement. Multiple feeder vessels are seen on angiography.

Treatment is indicated when vision is threatened by amblyopia as a result of anisometropia, ptosis or strabismus.

Intralesional injection of steroids is the most frequently used method. Usually 40-80 mg of triamcinolone with 25 mg of methylprednisolone is directly injected into the lesion.1 Alternatively Triamcinolone 40 mg along with betamethasone 4 mg can also be used. The tumor usually begins to regress in two weeks but if necessary injection may be repeated after about two months. Early recognition and prompt treatment with intralesional steroid prevents early occlusion amblyopia, but follow-up and management of refractive amblyopia with glasses and patching is necessary in the longer term. Potential complications include skin depigmentation, fat atrophy, eyelid necrosis and rarely central retinal artery occlusion.

Systemic steroids are indicated for extensive lesions especially if associated with visceral involvement. Recommended dosage used is 1.5 to 2.5 mg/kg prednisolone daily over a few weeks with titration downward depending on response.1

Though steroids are effective in large majority of patients, a recurrence is not infrequent. Recurrent or resistant cases are being treated with recombinant interferon alpha-2a and 2b with variable results.31 Recent studies have demonstrated good efficacy of interferons when given subcutaneously in a dose of 3 million units/m2. During clinical follow-up diagnostic ultrasound evaluation ( the depth dimension) proved helpful. One report suggested high efficacy of treatment when a combination of interferon alpha-2a with a low dose of cyclophosphamide.

In the presence of very large platelet-consuming lesions as seen with Kasabach-Meririt syndrome, systemic antifibrinolytics like aminocaproic acid or tranexemic acid are used.30

Surgical resection is carried out in cases where vision is threatened or there is a failure of medical management. Surgery should be carried out under hypotensive anesthesia with constant hemostasis during removal.32

Hemangiopericytoma

These are uncommon vascular tumors of the orbit occurring in the middle ages. They are divided into benign and malignant based upon the histopathology. Clinical features include progressive painless proptosis of usually less than one year duration, predominantly in the superior part of orbit. Hemodynamically there is rapid circulation with significant shunting of blood. CT and MRI shows well defined lesions with homogenous contrast enhancement.33 The microscopic features include cellular, myxoid and storiform components with spindle shaped pericytes, which stain positively with vimentin upon immunohistochemistry.34

Management includes careful and complete excision. The tumor has a pseudocapsule and is notorious for recurrences. Histologically benign tumors have been reported to metastasize. A very aggressive local behavior may warrant an exenteration.35

Angiosarcoma

Angiosarcomas are malignant tumors of the endothelial origin, with an affinity for the head and neck regions. Mostly affects males in 6-8th decades of life. They are ill defined, multiple, involving the skin of the lids and the orbit.36 They may present with orbital apex syndrome and other neurological deficits37 Since these tumors are aggressive, a wide surgical excision is adviced.

Kaposi's Sarcoma

Kaposi sarcoma has generated considerable research after the advent of AIDS.38 Though it is reported to be common in the western literature, we are yet to see a single case. Ocular involvement is usually of the skin, lids or conjunctiva as reddish or purple lesions and rarely lacrimal gland is involved.39 Histologically vascular slit channels lined by endothelium are seen.

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Management includes the use of chemotherapy and extended field radiotherapy.

Hemangioendothelioma

These are very rare tumors of the orbit. It is known to affect all age groups with no age or sex prelidiction. Multifocality is present in 9-14% of the cases.40

It presents as a very rapidly enlarging mass with edema or erythema of overlying skin. The tumor is highly vascular and bleeds significantly on biopsy. Unlike rhabdomyosarcoma, it has a mass effect rather than being invasive. Imaging modalities used are CT and MRI, which demonstrates lytic, multiloculated, expansile lesions of the orbit. Histopathologically the tumor is composed of irregular vascular elements lined with immature endothelial cells with prominent anaplasia. All hemangioendotheliomas are positive for at least one endothelial marker. (CD31, CD34, factor VIII ). Management includes histological grading followed by treatment with radiotherapy, chemotherapy and surgical removal.41

Hemangioblastoma

Hemangioblastoma is a rare tumor of the orbit. It presents with progressive proptosis which can be axial and abaxial as hemangioblatomas have been reported both from the recti muscles42 and optic nerve.43 Optic nerve hemangioblastomas are frequently familial, presents with visual loss and RAPD and are associated with infratentorial hemangioblastomas, angiomatosis retinae, and cysts of the abdominal viscera. CT and Magnetic resonance imaging reveals a wellenhanced mass, with an enlargement of optic canal in cases of optic nerve lesions. Management includes surgical removal with appropriate orbitotomy approaches.43

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CASE ILLUSTRATIONS

Case 1

Mrs. B, female 45 years in age, has presented with proptosis of her right eye since 5 years and progressive loss of vision since 3 years. There was no history of pain, trauma, change with posture, or any systemic disease. She consulted an ophthalmologist elsewhere 2 years back, who ordered CT scan of orbit which was reported as Meningioma of optic nerve sheath by the radiologist and hence was advised conservative management by the ophthalmologist.

On inspection, (Figure 10.1) she had a nonpulsatile proptosis of her right eye with displacement of globe by 8 mm axially, and outwards by 5 mm.There was no change with Valsalva maneuver. Fullness was seen with obliteration of superior sulcus. Minimal mechanical restriction of ocular motility was noticed. Pupil was dilated in size and direct light reaction was absent. There was no perception of light. Fundus exam revealed optic atrophy.

Non-tender, firm mass was palpable in the superior peripheral space, extending into Orbit. Its posterior border could not be felt. Orbital rim was normal. Retropulsion was positive.

General examination was within normal limits. Clinical Impression: In view axial proptosis, the lesion should be in the intraconal space. The long duration of proptosis, absence of visual symptoms for a long period after the onset of proptosis, and the severe degree of proptosis exclude lesions arising from optic nerve or its sheath. (We are yet to see a case of Meningioma of optic nerve sheath causing such a huge proptosis). In view of the long duration, sex (female) and the location (Cavernous hemangioma is the most common intraconal lesion in our experience), we made a diagnosis of

Cavernous hemangioma.

CT scan of orbit revealed a huge, hyper dense lesion, occupying entire intraconal space and extending into the peripheral space, more on the medial compartment, pushing the globe temporally (Figures 10.2 and 10.3). The lesion is very well encapsulated. It has caused excavation of bony orbit. It is not enhancing on contrast. All these features are

Vascular Lesions of Orbit 157

suggestive of Cavernous hemangioma. The tumor was excised through lateral orbitotomy. On gross examination it was very well encapsulated, measuring 55 mm × 45 mm (Figure 10.4). Histopathology confirmed it to be Cavernous hemangioma (Figure 10.5). Postoperative recovery was smooth and satisfactory but for mild enophthalmos which was due to increased orbital volume because of excavation of orbital walls (Figure 10.6).

Figure 10.1: Proptosis left eye with globe pushed temporally

Figure 10.4: Gross specimen Figure 10.5: Histopathology shoof excised Well encapsulated wing dilated vascular channels tumor (H and E) cavernous hemangioma

Figure 10.6: Postoperative picture showing relief from proptosis

Case 2

Mr. K, male, 32 years of age presented to us with painless progressive proptosis of right eye since 3 years. There was no history of defective vision, or diplopia.

On examination (Figure 10.7) we noticed eccentric proptosis of the right eye, with fullness inferiorly. The proptosis was nonpulsatile. Ocular motility was normal. Pupil was normal. There was no RAPD. Vision was 20/20 and color vision was normal. CT scan showed a well defined lesion in the inferior peripheral space with minimal contrast enhancement and bony excavation of the floor of the orbit (Figures 10.8 and 10.9), suggestive of Cavernous hemangioma.

Anterior inferior orbitotomy was performed through subciliary approach, and the tumor was exsanguinated by passing a suture through the substance of it to shrink its size (Figure 10.10). This suture also helps in applying traction to assist the excision of the tumor through a smaller incision .

The excised tumor was pinkish in color and was very well encapsulated. (Figure 10.11) The cut-section of the tumor (Figure 10.12) showed honey-comb like appearance with blood oozing out from the entire cut surface. On histological examination the encapsulated mass was made-up of dilated vascular channels, filled with blood (Figure 10.13), confirming the clinical diagnosis of Cavernous hemangioma. The patient recovered well (Figure 10.14). The proptosis disappeared completely. His vision remained 20/20. The ocular motility was full.

Figure 10.7: Eccentric proptosis with inferior fullness

Figure 10.10: Suture through Figure 10.11: Well encapsulated exsanguinated and shrinks Aids tumor

excision by traction

Figure 10.12: Cut section showing Figure 10.13: Dilated vascular honeycomb appearance with blood channels filled with blood oozing from it

There was no recurrence of the tumor. The points to consider in this case were the location of cavernous hemangioma in the inferior peripheral space, the passing of suture through the hemangioma to bleed the tumor and shrink its size, which facilitates to remove the tumor through a smaller incision. Cryo is other wise an excellent tool to hold the tumor during its dissection and removal.

Case 3

Mrs. J, a female 28 years of age, presented with history that her friends and family members were commenting that her right eye was looking prominent since 3 months (Figure 10.15). She had no pain and did not complain of any visual disturbances. Past history was significant in that she had convulsions 4 years back and CT scan of brain showed 2 calcified lesions (Figure 10.16). She was on carbamazepine (Tegretol) since then. There was no relapse of convulsions. On clinical evaluation, she had 3 mm of axial and nonpulsatile proptosis, which did not increase with Val-salva maneuver. The ocular motility was normal. The pupils were brisk and the vision was 20/20. CT scan of orbit revealed a hyper-dense, contrast enhancing lesion of size 15 × 12 mm in the intraconal space (Figures 10.17A and B). In view of the short duration and contrast enhancement, provisional diagnosis of a vascular tumor like hemangioendothelioma/hemangiopericytoma was considered. Lateral orbitotomy was performed and the tumor was excised. Histopathology and Immunohistochemistry revealed it to be hemangioblastoma. Further evaluation of the patient did not show any

Figures 10.17A and B: Axial and Coronal sections of CT orbit showing well encapsulated Intraconal lesion with contrast enhancement

Figure 10.18: Postoperative status showing complete recovery

other lesions in the posterior segment of the globes, brain or elsewhere. The calcified lesions are probably intracranial hemangioblastoma and since they were inactive, neurosurgeon did not contemplate excision. The patient has no recurrence during the past 3 years of follow-up (Figure 10.18).

Case 4

Miss P, female child of 6 years presented with acute proptosis of 2 weeks duration associated with severe pain and defective vision. There was no history of trauma.She never had similar problem previously.

On examination she had a non-pulsatile, proptosis of 7 mm, associated with severe periocular fullness, chemosis grade III associated with subconjunctival

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hemorrhage, and restricted ocular motility in all gazes .Pupil was dilated. RAPD was present. Her best corrected vision was 20/200. Retropulsion was positive. Tenderness was present on palpation (Figure 10.19).

In view of acute onset associated with pain, chemosis, restricted motility, subconjunctival hemorrhage and chemosis, in a child, Lymphangioma was the clinical diagnosis. CT scan showed a contrast enhancing lesion with a huge hemorrhage in the lesion, supporting the clinical diagnosis (Figure 10.20). Normally lymphangioma is managed conservatively since it is not possible to excise it completely and hence recurrence is very common. But in this child as the vision is being compromised, the parents were informed that though recurrence is very common, surgery was to be performed to save vision. Antero-lateral orbitotomy was performed. About 6 cc of blood was aspirated from the lesion to shrink it and excised as much as possible (Figure 10.21). The histopathology confirmed the diagnosis of lymphangioma (Figure 10.22). Postoperative recovery was smooth and the vision improved to 20/20 (Figure 10.23). After 3 years, she had a

Figure 10.19: Acute proptosis Figure 10.20: CT scan of orbit with severe chemosis and showing large cystic lesion in periocular swelling intraconal space extending to medial peripheral space, and

hemorrhage within

Figure 10.23: Postoperative status. Proptosis disappeared vision improved to 20/20

recurrence which was surgically managed. There was no recurrence in the 2 year postoperative follow-up after second surgery.

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2.Harris GJ Orbital vascular malformations: a consensus statement on terminology and it clinical implications. Orbital society. Am J Ophthalmol. 1999; 127:453-55.

3.Rootman J, Hay E, Graeb D, et al. Orbital adenexal lymphangiomas. A spectrum of hemodynamically isolated vascular hamartomas. Ophthalmology. 1986; 93:1558-70.

4.Pang P, Jakobiec FA, Iwamoto T, Hornblass A Small lymphangiomas of the eyelids. Ophthalmology 1984; 91:1278-84.

5.Kazim M, Kennerdell JS, Rothfus W, et al. Orbital lymphangioma: correlation of magnetic resonance images and intraoperative findings. Ophthalmology. 1992; 99: 1588-94.

6.Harris GJ, Sakol PJ, Bonavolontu G, et al. An analysis of 30 cases of orbital lymphangiomas: pathophysiological considerations and management recommendations. Ophthalmology. 1990; 97:1583-91.

7.C Luzzatto, P Midrio, Z Tchaprassian, M Guglielmi: Sclerosing treatment of lymphangiomas with OK-432. Arch Dis Child 2000;82:316-318.

8.CM Giguere, NM Bauman, Y Sato, DK Burke, JH Greinwald, S Pransky, P Kelley, K Georgeson, and RJH Smith Treatment of Lymphangiomas With OK-432 (Picibanil) Sclerotherapy: A Prospective Multi-institutional Trial Arch Otolaryngol Head Neck Surg, October 1, 2002; 128(10): 1137-44.

9.JP Deveikis. Percutaneous Ethanol Sclerotherapy for Vascular Malformations in the Head and Neck Arch Facial Plast Surg, September 1, 2005; 7(5): 322-5.

10.Mathur NN, Rana I, Bothra R, Dhawan R, Kathuria G, Pradhan T Bleomycin sclerotherapy in congenital lymphatic and vascular malformations of head and neck. Int J Pediatr Otorhinolaryngol. 2005;69(1):75-80.

11.Schwarcz RM, Ben Simon GJ, Cook T, Goldberg RA Sclerosing therapy as first line treatment for low flow vascular lesions of the orbit. Am J Ophthalmol. 2006;141(2):333-9.

12.Wojno TH Sotradecol (sodium tetradecyl sulfate) injection of orbital. Lymphangioma. Ophthal Plast Reconstr Surg. 1999;15(6):432-7.

13.Wright JE, Sullivan TJ, Garner A, et al. Orbital venous anomalies. Ophthalmology. 1997; 104:905-13.

14.Cline RA, Rootman J. Enophthalmos: a clinical review. Ophthalmology. 1984; 91:229-37.

15.Harris GJ, Jakobiec FA. Cavernous hemangioma of the orbit: A clincopathological analysis of sixty-six cases. In: Ocular and adnexal tumors. Birmingham, AL: Aesculapius, 1978:741-81.

16.Fries PD, Char DH. Bilateral orbital cavernous hemangiomas. Br J Ophthalmol 1988; 72:871-3.

17.Sullivan TJ, Aylward GW, Wright JE, et al. Bilateral multiple Cavernous hemangiomas of the orbit. Br J Ophthalmol. 1992; 76:627-9.

18.Forbes GS, Sheedy PF, Waller RR. Orbital tumors evaluated by Computer tomography. Radiology 1980;136:101-11.

19.Ohtsuka K, Hashimoto M, Akiba H. Serial dynamic magnetic resonance imaging of orbital cavernous hemangioma. Am J Ophthalmol. 1997; 123:396-8.

20.Susac JO, Smith JL, Scelfo RJ The "tomato catsup" fundus in Sturge-Weber syndrome. J Pediatr Ophthalmol Strabismus. 1974; 92:69-70.

21.Phelps CD The pathogenesis of glaucoma in Struge-Weber Syndrome. Ophthalmology. 1978; 85:276-86.

22.Kim J, Kim OH, Suh JH, Lew HM Wyburn-Mason syndrome: An unusual presentation of bilateral orbital and unilateral brain A-V malformations. Pediatr Radiol. 1998; 28:161.

23.Good WV, Hoyt CS Optic nerve shadow enlargement in Klippel. Trenaunay-Weber syndrome. J Pediatr Ophthalmol Strabismus. 1989; 26:288-9.

24.Barrow DL, Spector RH, Braun IF, et al. Classification and Treatment of spontaneous carotid-cavernous sinus fistulas. J Neurosurg 1985; 62:248-56.

25.Talusan ED, Fishbein SL, Shwartz B Increased pressure of dilated episcleral veins with open angle glaucoma without exophthalmos. Ophthalmology. 1983; 90:257-65.

26.Vinuela F, Fox AJ, Debrun GM, et al. Spontaneous carotidcavernous fistulas: clinical, radiological and therapeutic considerations. J Neurosurg. 184; 60:976-84.

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27.Debrun GM, Vinuela F, Fox AJ, et al. Indications for treatment and classification of 132 carotid-cavernous fistulas. Neurosurg. 1988; 22:285-9.

28.Lasjaunias P, Chiu M, Ter Brugge K, et al. Neurological manifestations of intracranial dural arterio-venous malformations. J Neurosurg 1986; 64:724-30.

29.Haik BG, Jakobiec FA, Ellsworth RM, Jones IS. Capillary hemangioma of the lids and orbit: an analysis of the clinical features and therapeutic results in 101 cases. Ophthalmology 1979; 86:760-92.

30.Neidhart JA, Roach RW. Successful treatment of skeletal hemangioma and Kasabach-Merritt syndrome with aminocaproic acid. Am J Med 1982; 73: 434-8.

31.Teske S, Ohlrich SJ, Gole G, et al. Treatment of orbital capillary hemangioma with interferon. Aust N Z J Ophthalmol 1994; 22: 13-7.

32.Walker RS, Custer PL, Nerad JA. Surgical excision of periorbital capillary hemangiomas. Ophthalmology 1994; 101:1333-40.

33.Kikuchi K, Kowada M, Sageshima M Orbital hemangiopericytoma: CT MRI and angiographic findings. Comput Med Imaging Graph. 1994;18:217-22.

34.Croxatto JO, Font RL. Hemangiopericytoma of the orbit: A clinico-pathological study of 30 cases. Hum Pathol 1982; 12:210-18.

35.Sullivan TJ, Wright JE, Wulc AE, et al. Hemangiopericytoma of the orbit. Aust N Z J Ophthalmol . 1992; 20:325-32.

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40.Arie R, Aylon YG, Don R Hemangioendothelioma of the orbit. Intl J Pediatric Otorhinolaryngology. 2006;1:188-91.

41.Lyon DB, Tang TT, Kidder TM Hemangioendothelioma of the orbital bone. Ophthalmol 1992. 99:1773-98.

42.Cockerham KP, Sachs DM, Cockerham GC, Hidayat AA, Brown HG Orbital hemangioblastoma arising in a rectus muscle. Ophthal Plast Reconstr Surg. 2003 May;19(3): 248-50.

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Optic Nerve Glioma

The first clinical report of optic nerve tumors was by Antonio Scarpa in 1816, however it wasn't until 1912 that Hudson described optic nerve gliomas and optic meningiomas as separate lesions.1 These tumors are relatively rare, accounting for less than 4% of all orbital tumors. Overall optic nerve gliomas account for 65%1,2 of optic nerve tumors and meningiomas 35%.1 Optic nerve gliomas appear to be more frequent in females, whereas for optic pathway gliomas, there may be an equal sex distribution.2 Lesions typically become symptomatic in childhood.3 The mean age of presentation is 8.8 years with only 10% presenting after 19 years of age.2 Most lesions are sporadic although there is an association with neurofibromatosis (NF 1). Adult optic nerve gliomas may behave like those presenting in childhood,3 however some may show an aggressive behavior, being clinically distinct from those seen in childhood. These patients are typically middle aged with a slight male bias.3

Benign optic nerve gliomas are typically pilocytic astrocytomas originating from astrocytic glia and can involve the visual pathways anywhere from the optic nerve to the visual cortex.1,4 Histologically they are composed of delicate, hair-like elongated eosinophilic cells in an interwoven pattern. The nuclei may be round or oval. Mitoses are rare, but nuclear atypia may be observed. Malignant change is very rare. The proliferating astrocytes in an optic glioma may be associated with worm-like densely eosiniophilic bodies, known as Rosenthal fibers, surrounded by hyalinized connective tissue, a

distinctive (but not diagnostic) feature of pilocytic astrocytomas.5 Orbital gliomas, particularly in patients suffering from NF 1, can extend through the pia and arachnoid matter in to the subdural space. They tend to remain intradural, however when incompletely excised can recur diffusely invading adjacent orbital structures. Where the lesion has spread to the subarachnoid space reactive proliferation of fibrovascular and meningeothelial tissue can occur resulting in arachnoid hyperplasia, which can resemble an optic nerve sheath meningioma.1 Two patterns of growth are identified, perineural (circumferential growth) and intraneural growth. Perineural growth results from proliferating astrocytes and fibrovascular tissue within the dural sheath, widening the epipial-subdural space and subsequently compressing the optic nerve. Intraneural growth results from growth of intra-axial astrocytes causing the subarachnoid space to be obliterated. Perineural growth appears to occur in patients with NF1.1 Enlargement of optic gliomas occurs by a combination of neoplastic cell proliferation, reactive arachnoid proliferation and accumulation of PAS positive mucinous substance. Rapid growth can result from cystic degeneration or intra-lesional hemorrhage. Malignant change can occur however this is extremely rare.1

Malignant optic nerve gliomas seen in adults show evidence of malignant astrocytomas and are thought to originate within the optic pathways. Extension is usually subpial along the optic pathways although can directly invade the substance of the brain.1