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

Approximately 30-50% of benign optic gliomas are associated with neurofibromatosis type 1 (NF 1)2, 4, the rest occur sporadically. The incidence of optic nerve glioma in patients with NF 1 is 15-20% of which only about 20% have visual symptoms.1, 4

The presenting symptoms depend very much on the location of the lesion. Those involving predominantly the intraorbital optic nerve present with proptosis, ocular motility abnormalities, vision loss and visual field loss. Intracranial tumors including those involving the chiasm, tend to have reduced vision and endocrine abnormalities including precocious puberty.1-4 Fundoscopy may reveal either optic atrophy or papilloedema depending on the location of the lesion. Optocilliary shunt vessels, central retinal vein occlusion and venous stastis retinopathy are occasionally seen.1,3 Hemorrhage in to the tumor can result in acute proptosis and sudden loss of vision.3

Investigation of optic nerve gliomas involves computerized tomography (CT) and magnetic resonance imaging (MRI). The appearance of the lesion depends on whether the patient has NF 1 or not. Fusiform swelling of the optic nerve is typically seen in patients without NF 1, whereas those with NF 1 tend to have more irregular nerves with areas of kinking or buckling.3 Cystic spaces may occasionally be seen representing mucinous accumulations. With perineural growth patterns, there may be thickening of the dura with preservation of the compressed optic nerve, mimicking the tramtracking seen in optic nerve sheath meningiomas. Calcification is a rare finding.1 MRI shows the lesions to be hypointense on T1 weighted images, whereas on T2 images the glioma tends to be hyperintense.3 Contrast enhancement and fat suppression technique can help to differentiate optic nerve meningiomas from gliomas, since arachnoid hyperplasia associated with gliomas does not enhance with gadolinium.1

Treatment options depend very much on the location and extent of the lesion. Most optic nerve gliomas have an indolent growth pattern and can remain stable for many years, with some spontaneously regressing.1, 3 Those lesions confined to the optic nerve show a mortality rate of 5% from intracranial extension. Tumor resection is curative

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whilst the lesion remains confined to the optic nerve. Lesions involving the chiasm have a mortality rate of approximately 28% from intracranial spread, whilst hypothalamic or 3rd ventricle involvement increases the mortality rate to more than 50% at 15 years.1 Patients with isolated optic nerve involvement and good vision should be reviewed on regularly with repeat serial MRI scans of the optic nerve. When there are signs of posterior progression the lesion should be excised en block.1 Those lesions confined to the optic nerve in blind, painful or cosmetically unacceptable eyes should be considered for surgical excision.1,3,4 Optic nerve lesions extending to the chiasm or those primarily involving the chiasm or optic tracks could be considered for chemotherapy or radiotherapy. Children 5-7 years and younger should be treated with chemotherapy2,4 since radiotherapy at this age may result in damage to the endocrine system and affect the future intellectual development of the child.1,4 Children aged 10 and above may be considered for radiotherapy using various delivery techniques. Doses typically given are in the range of 45 to 56 Gy given in 180cGy fractions.

Malignant glioma seen in adults is invariably fatal.1 Neuro-imaging of an involved optic nerve is non-specific and the condition shows a rapid rate of progression. Lesions affecting the proximal part of the optic nerve can progress to affect both eyes within 5-6 weeks.3

Optic Nerve Meningioma

Optic nerve meningiomas account for one third of primary optic nerve tumors and were first identified as a pathological entity in 1835 by Jean Cruveilheir. It wasn't until 1912 that Hudson clearly differentiated optic nerve gliomas from meningiomas.6 Most meningiomas involving the orbit are extensions from intracranial sites such as the sphenoidal wing (secondary optic nerve sheath meningiomas). Primary optic nerve meningiomas originate from the cap cells of the arachnoid surrounding the intraorbital or intracanalicular portion of the optic nerve.3 The typical age at presentation is 40 years of age6,7 with bilateral cases presenting much earlier at approximately 13 years of age.6 There is a small sex bias with 61% of cases occurring in females.6

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Histologically most orbital meningiomas are of the meningiothelial or syncytial variety. The cells are eosinophilic with abundant cytoplasm and indistinct cell margins. The nuclei are small and vesicular with occasional pseudoinclusions. Cells may be wrapped with or without psammoma bodies in tight whorls.5 Approximately 90% of meningiomas involving the orbit originate from intracranial sites, primarily the olfactory groove and the sphenoidal ridge.6 Ectopic lesions have been described in the orbit, seemingly independent of the optic nerve, these may have developed from orbital mesenchymal cells or may be a case of mistaken identity, since lesions such as fibroxanthomas and hemangiopericytomas closely resemble meningiomas.6

NF 1 is associated with optic nerve meningioma, although the relationship is no where near as high as for optic nerve glioma. The incidence of NF 1 in patients with optic nerve meningioma is 2%, whereas the incidence of NF 1 in the general population is 0.03-0.05%.6

The classical triad of clinical findings in optic nerve meningioma are visual loss, optic atrophy and optociliary shunt vessels.3,6 The simultaneous occurrence of these three findings is however rare. The most common finding is vision loss which can take the form of visual obscurations. Other findings are reduced color vision and visual field defects.3,6 Proptosis seems to follow the onset of visual loss, tending to be reasonably mild.3,7 It is thought to occur because tumor growth results in a straightening of the optic nerve and may also account for any ocular motility defects with up gaze being most commonly affected.6,7 Orbital pain may occur. Examination may reveal disc swelling although the only signs may be optic atrophy. Optociliary shunts which present in less than one third of patients3,7 are shunts between the retinal and choroidal circulations and thought to be a result of a reopening of regressed vestigial embryonic retinociliary anastomoses.6 They may be seen in eyes with other causes of disc swelling. The disc swelling and central retinal vein congestion may proceed the shunt vessels by 1-2 years becoming noticeable as the swelling starts to resolve3 and then regress as optic atrophy sets in.6

Meningiomas arise from meningothelial cells along the meninges. Large collections are known as

pachionian bodies or arachnoid bodies whereas smaller ones are known as arachnoid villi. Optic nerve meningiomas are thought to arise from meningiothelial cap cells of the arachnoid villi.6 Two patterns of growth are seen, a syncytial pattern in which polygonal cells are arranged in sheets separated by vascular trabeculae and a transitional pattern where spindle cells are arranged in concentric whorls. Mitoses are uncommon. Psammoma bodies are occasionally seen in which calcium salts can be deposited. Meningiomas may spread in the subarachnoid spaces along paths of least resistance. They can extend in to the surrounding tissues3 and the haversian canal system of bone resulting in hyperosteosis. They do not seem to invade the brain and are not associated with raised intracranial pressure or pituitary dysfunction.6 Growth is slow although may accelerate with pregnancy and results in compression of the optic nerve.6

Investigation involves CT and MRI imaging. Calcification when present is useful in distinguishing optic nerve gliomas from meningiomas. Typically the lesions show 'tram-tracking' in which a thickened optic nerve sheath surrounds a central lucent optic nerve.3,6,7 On coronal views this is seen as a dense ring surrounding the central optic nerve.6 MRI with gadolinium enhancement is particularly sensitive in detecting meningiomas.7

Treatment options include surgery and radiotherapy, however observation is not unreasonable since the mortality rate is low.7 Surgery may be indicated for aggressive lesions however it is associated with a high degree of local recurrence and orbital invasion. Typically surgical excision results in blindness, since the tumor and optic nerve often share their blood supply.6,7 Decompression of the nerve has been attempted by opening the dural sheath, which in some cases can arrest the visual deterioration.3,6 Fractionated radiotherapy with a total of 40-54Gy given in divided doses seems to be effective in stabilizing and in some cases improve vision, whilst at the same time limiting the risks of optic nerve or chiasm damage to less than 5%.3,7,8 Interestingly the tumor volume appears unchanged following radiotherapy, despite an improvement in neurological function.8 The side effects of treatment including headache, nausea and hair loss can be

limited by fractionating the doses. Later side effects include pituitary dysfunction, retinopathy, iritis and temporal lobe atrophy.8 The risk of optic nerve or chiasm damage associated with high doses of radiotherapy. When doses greater than 59Gy are given in fractions of less than 1.9Gy there is an 11% risk of injury whilst doses greater than 1.9Gy have a 47% risk according to a University of Florida study.9 Low dose steroids at the time of radiotherapy may limit damage from radiation induced peritumor edema.8 The risk of a second malignancy following radiotherapy is 0-2% at 10-20 years.8 When a lesion is treated with a single dose of radiation the threshold for injury is 8-10 Gy.8

Orbital Schwannoma (Neurilemmoma) and Neurofibroma

Schwannomas also known as neurilemmomas account for approximately 1-4% of orbital tumors, occurring most commonly in men between the second and fifth decades.10,11 They occasionally arise from the optic nerve, probably originating from schwann cells of sympathetic nerves tightly adherent to the optic nerve.3 More frequent sites are the other cranial nerves including the oculomotor, lacrimal, trigeminal and zygomaticotemporal nerves.10,11 The most commonly affected cranial nerve is the vestibular nerve.12

Schwannomas are slow growing lesions that do not invade surrounding tissues.11 Clinical features include proptosis and diplopia. Globe compression can induce a hypermetropic shift, whilst optic nerve compression results in reduced visual acuity. Malignant transformation is rare.10

Gross examination reveals a well encapsulated yellowish grey lesion, with cysts containing clear fluid. Histologically schwannomas show two growth patterns: Antoni A where densely packed spindleshaped cells are arranged with palisaded nuclei sometimes forming Verocay bodies, and Antoni B where cells are separated by an abundant myxoid stroma with no alignment of nuclei. Mitoses are usually absent. The associated nerve may sometimes be seen in one side of the lesion, in contrast to a neurofibroma where the originating nerve is expanded by the lesion and cannot be seen. So-called "ancient schwannomas" may feature bizarre enlarged or multiple nuclei, but there are no malignant

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connotations.10,13 The lesions may be very vascular, causing diagnostic confusion.

Surgery is the treatment of choice11 although it is associated with usual risks of orbital surgery including loss of sight. Recent advances in steriotactic radiosurgery and fractionated radiotherapy in the treatment of vestibular schwannoma and nonvestibular schwannoma have achieved high levels of tumor growth control whilst preserving cranial nerve function.12,14 Future advances may mean that this treatment option could be used to treat and control orbital schwannomas.3

Neuro-imaging reveals a homogenious lesion isointense with rest of the surrounding neural tissue mimicking other lesions such as optic nerve gliomas, cystic spaces are sometimes seen.3,11 Histopathology is required to make a definitive diagnosis.10,11,15

Neurofibromas are another group of benign nerve sheath tumors which can occur in the orbit region.16 In a retrospective review by Rose et al. in 1991,17 looking at peripheral nerve tumors in the orbit, they found that 93% of these lesions were either schwannomas (neurilemmomas) or neurofibromas. In their series they found that most affected nerve was the first division of the trigeminal nerve.

Neurofibromas are typically associated with neurofibromatosis, although they can occur in isolation. Approximately 25 to 45% of all lesions are found in the head and neck region.16 Other sites typical affected by neurofibromas include the eyelids, the orbit and rarely the lacrimal sac.18

Clinically they tend to present with painless proptosis and diplopia. Pain and altered sensation are rare.17

Grossly, the lesions appear as an encapsulated firm white mass. Histologically neurofibromas consist of wavy cells with basophilic nuclei.16

The treatment of choice is surgical excision. Even when incompletely excised recurrence is low.17

When to Suspect an Orbital Tumor of Neurological Origin

•Insidious onset

•Proptosis typically axial

•Symptoms may include: Pain with and without eye movement, diplopia, blurring of vision, reduced color vision and increased hypermetropia

166 Surgical Atlas of Orbital Diseases

•Fundoscopy may include: Unilateral disc swelling and choroidal folds

•Firmness of the globe to retropulsion.

Investigations

•Bloods to rule out an inflammatory cause

•Orbital imaging: CT and/or MRI imaging preferably with contrast enhancement

•Orbital biopsy where imaging is suspicious or the diagnosis is in doubt.

CASE ILLUSTRATIONS

Case 1

A 2 years old child with Neurofibromatosis type 1 was referred to the eye department by the pediatric oncology service following surgery for a cerebellar astrocytoma and hydrocephalus.

At presentation she had an unrelated right convergent strabismus for which she underwent convergent squint surgery. Fundoscopy including the optic disc was unremarkable and there was no RAPD. There was no evidence of proptosis.

Routine MRI scans (Figures 11.1 and 11.2) revealed sub-clinical bilateral optic nerve gliomas.

Figure 11.1: Bilateral optic nerve glioma (axial view)

Over the following 8 years optic disc cupping developed, with the left disc being paler and more cupped. Color vision remained normal in both eyes.

Case 2

A 66 years old female presented to the orbit clinic with a 6 months history of horizontal diplopia. Visual acuity was 6/9 in the right eye and 6/12 in the left. Ocular motility appeared normal however diplopia was reported on dextroversion. There was proptosis of 4 mm on the left and a left relative afferent papillary defect. Only 2 of 13 ishihara plates were correctly identified by the left eye whereas color vision in the right eye was normal. There was no evidence of papilloedema, although the left disc was slightly pale. Fundoscopy revealed signs of age related macular degeneration in both eyes. Routine bloods were taken.

Urgent MRI and CT scans were performed, revealing an intraconal soft tissue mass which involved the sphenoidal wing and extending intracranially to the temporal lobe (Figure 11.3). The findings were strongly suggestive of a meningioma. A subsequent CT scan showed evidence of hyperostosis of the sphenoidal wing, as well as bone loss in the posteriorlateral aspect of the orbit. The diagnosis of a sphenoidal wing meningioma was made.

A neurosurgical referral was made and the patient was offered the option of a craniotomy and surgical debulking of the tumor. As there was no guarantee that this would improve her vision, surgery was declined. The condition is being managed conservatively with regular clinic follow up and routine repeat MRI scans.

Case 3

A 66 years old female was referred from a district hospital with retro-orbital pain. An MRI had revealed

an intraconal retrobulbar mass displacing the optic nerve superiorly, with no evidence of bone destruction. Visual acuity was 6/9 in the right eye and 6/6 in the left. Color vision slightly reduced in the right eye, seeing 13 out of 15 ishihara plates, the left was normal. A mild right RAPD was noted. Both optic discs were normal and there was no proptosis. A diagnosis of optic nerve meningioma was made. Following discussion with the patient and oncology/ radiotherapy department a dose of 50.4 Gy was given in 14 fractions to the orbit.

Subsequent MRI scans revealed a reduction in the tumor following the radiotherapy. After treatment the patient experienced a dry right eye, which was treated with lubricants, and there was evidence of mild radiation retinopathy.

Case 4

A 74 years old female with a known optic nerve meningioma was referred to the orbital clinic with a recurrence of orbital symptoms and enlargement of the lesion. Visual acuity in the affected eye was NPL, whereas the right was 6/6. Proptosis was noted on the left side. The left disc was atrophic and there was marked chorioretinal atrophy. An MRI confirmed enlargement of the lesion with extension towards the orbital apex. Following discussion with the patient a decision was made to debulk the meningioma via a lateral orbitotomy. Histology confirmed the diagnosis of a meningioma (Figures 11.4 and 11.5).

Case 5

A 36 years old male attended the orbit clinic with an 18 months history of worsening left sided proptosis (Figure 11.6). Visual acuity was unaffected; left eye 6/6, right 6/5, although color vision was slightly reduced, with only 11 out of 13 ishihara color vision plates being correctly identified in the left eye. Color vision was normal in the right eye. The visual field on the left showed generalized depression on the left side although no relative afferent papillary defect was identified. Oculomotor function was reduced on abduction and upgaze in the left eye. Fundoscopy of both eyes was normal with no evidence of papilloedema. The central nervous system examination was unremarkable and there was no past medical history of relevance.

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Figure 11.4: Low power meningioma H and E stain

Figure 11.5: High power meningioma H and E stain

Figure 11.6: Left sided proptosis

An urgent MRI scan of the orbits was arranged identifying a 2.5 cm rounded intraconal lesion which was enhanced following intravenous contrast administration (Figure 11.7). The optic nerve, lateral and inferior rectus were displaced and that the lesion was intraconal (Figure 11.8). The optic nerve was separate from the lesion. An MRI scan was also

168 Surgical Atlas of Orbital Diseases

Figure 11.7: Left orbital schwannoma axial view

Figure 11.8: Left orbital schwannoma sagittal view

organized overall the MRI and CT findings suggested the lesion was a possible cavernous hemangioma. An urgent excision biopsy was arranged via a lateral orbitotomy approach.

Macroscopically the tumor was found to be cystic and wrapped around optic nerve. The lesion was debulked. As the surgery proceeded the pupil became fixed and dilated. No further debulking was attempted and the wound closed.

Postoperatively the pupil gradually recovered and vision remained 6/6.

Histopathological examination revealed the lesion to be a cystic Schwannoma.

Referral was made to the oncology service and the tumor treated with radiotherapy.

Surgical Approach

Where orbital surgery is considered to obtain a tissue diagnosis or to debulk an orbital tumor, a lateral orbitotomy approach is chosen since this gives good access to the retro-orbital spaces and any lesions found there. If there is evidence of intracranial extension, referral to a neurosurgeon is indicated, a craniotomy may be indicated.

Lateral Orbitotomy

A lateral orbitotomy approach is employed to biopsy tumors arising in the anterior third of the orbit. The lateral 1/3 of the skin crease is marked with pen and extended down parallel to the lid margin to a height level with the lateral canthus. The line is then extended laterally in a horizontal plane for 1½ cm. Local anesthetic is injected subcutaneously in this region. A skin incision is made along this line with a cutting diathermy. The deep tissues are blunt dissected down to the periosteum. This is incised with the diathermy and the periosteum blunt dissected off the bone exposing the lateral wall from the frontozygomatic suture down to the lower border of the lateral wall just above the opening of the zygomaticofacial foramen. At the orbital rim the periobita is elevated off the internal aspect of the lateral wall of the orbit. The orbital contents are displaced nasally with a malleable retractor. Two holes ½ cm apart and ¾ cm back from the orbital margin are drilled parallel to the orbital rim at the superior border of the exposed bone and 2 at the bottom. A gap of approximately 3 cm will exist between the higher of the 2 lower holes and the lower of the upper 2 holes. The lateral orbital wall is incised with a power saw between the drilled holes both superiorly and inferiorly. The cuts extended for approximately 2 cm in a radial direction to an area where the bone thins. A malleable retractor should be used to protect the globe during this procedure. The section of bone is dissected off with forceps and stored in normal saline.

Once the lesion is identified care should be taken to avoid the globe, optic nerve and rectus muscles, while incision biopsies are taken using a 15° blade and forceps. Pupil reactions are monitored throughout the procedure. Hemostasis is achieved with bipolar cautery. The lateral orbital wall is replaced by threading 4.0 prolene through the

pre-holes at the orbital rim and tied in place. The tissues are closed with 5.0 vicryl and skin closed with 5.0 prolene. A reducing dose of steroids is given for 18 days along with a histamine H2 receptor antagonist such as ranitidine.

A head-light is worn throughout the procedure to ensure adequate illumination of the operating field. Where a drain is used this can be removed the following day.

REFERENCES

1.Dutton JJ. Gliomas of the anterior visual pathway. Survey of Ophthalmology 1994;38(5):427-52.

2.Jahraus CD, NJ Tarbell. Optic pathway gliomas. Pediatric Blood and Cancer 2006;46(5):586-96.

3.Miller NR. Primary tumours of the optic nerve and its sheath Eye 2004;18(11):1026-37.

4.Kaufman LM, O Doroftei. Optic glioma warranting treatment in children Eye, 2006. 20(10):1149-64.

5.Rosenblum MK, Bilbao JM Ang L Neuromucular system Chap 28 in Surgical Pathology Ed Rosai (9th ed) 2004;2:2461682.

6.Dutton JJ. Optic nerve sheath meningiomas. Survey of Ophthalmology 1992;37(3):167-83.

7.Carrasco JR, RB Penne. Optic nerve sheath meningiomas and advanced treatment options. Current Opinion in Ophthalmology 2004;15(5):406-10.

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8.Melian E, WM Jay. Primary radiotherapy for optic nerve sheath meningioma. Seminars in Ophthalmology, 2004;19(3-4):130-40.

9.Parsons JT, et al. Radiation optic neuropathy after megavoltage external-beam irradiation: analysis of timedose factors. International Journal of Radiation Oncology, Biology, Physics, 1994;30(4):755-63.

10.Subramanian N, et al. Cystic schwannoma of the orbita case series Orbit 2005;24(2):125-29.

11.Tezer MS, et al. Schwannoma originating from the infraorbital nerve: a case report. Auris Nasus Larynx 2006; 33(3):343-5.

12.Pollock BE, RL Foote, SL Stafford. Stereotactic radiosurgery: the preferred management for patients with nonvestibular schwannomas? Int J Radiat Oncol Biol Phys, 2002; 52(4):1002-7.

13.Rutherford SA, AT King. Vestibular schwannoma management: What is the 'best' option? Br J Neurosurg, 2005;19(4):309-16.

14.Tsuzuki N, et al. Cystic schwannoma of the orbit: case report. Surg Neurol, 2000;54(5):385-7.

15.Rosai J Soft Tissues Chap 25 in Surgical Pathology Ed Rosai (9th ed) 2004;2:2237-371.

16.Chua CN, Alhady M, Ngo CT, Swethadri GK, Singh A, Tan S Solitary nasal neurofibroma presenting as compressive optic neuropathy. Eye 2006;20(12):1406-8.

17.Rose GE, Wright JE. Isolated peripheral nerve sheath tumours of the orbit Eye 1991;5(6)668-73.

18.Dailey RA, Sullivan SA, Wobig JL. Surgical debulking of eyelid and anterior orbital plexiform neurofibromas by means of the carbon dioxide laser. American Journal of Ophthalmology, 2000;130(1):117-19.

Mesenchymal Soft Tissue Tumors

Tumors that are believed to arise from mesenchymal tissues occur in multiple sites with variable biologic behavior. In the orbit mesenchymal tissues include striated and smooth muscle, fibrous tissue, fat, cartilage, and bone. Bone tumors are discussed separately in Chapter 13. Despite orbital mesenchyme arising from neural crest, lesions do not differ from other locations in the body in which mesenchymal tissues arise from mesoderm. In our orbital center mesenchymal tumors account for 1.6% of orbital lesions and 9% of neoplasias; in children they constitute 5% of all disease and 19.4% of childhood neoplasia.1

Striated Muscle Tumors Rhabdomyosarcoma

Epidemiology

Rhabdomyosarcoma accounts for approximately 20% of all soft-tissue sarcomas making it the most common soft tissue sarcoma in children.2, 3 The head and neck is the principal location and the orbit the second most common site in the head and neck (the most common being the parameninges) accounting for about 10% of all rhabdomyosarcomas.4-6 Rhabdomyosarcoma is thus the most common primary orbital malignancy of childhood. In our clinic it constitutes 1% of all orbital neoplasias, and 6% in children.1

It has occurred from birth to the seventh decade, but 70% present in the first decade with a mean age of 8. The embryonal subtype affects mainly children, the alveolar mainly adolescents (median age 16), and

the much rarer anaplastic (pleomorphic) subtype most commonly presents in older people (median age is 54).7-11 Embryonal rhabdoymyosarcoma is the most common subtype accounting for 49% of all rhabdomyosarcomas and their predominance in the orbit is even greater since this subtype has a predilection for the orbit and parameninges.12

Most cases are sporadic although familial, congenital, and multiple tumors in the same patient including retinoblastoma have been reported.13 Most evidence suggests that they arise from primitive mesenchyme and not from skeletal muscle as they can develop in areas with no skeletal muscle.14

Presentation

The typical presentation is rapidly developing exophthalmos over weeks (mean of 5) with 60% presenting with signs of inflammation including conjunctival and eyelid swelling.9,10,15 Two-thirds of primary orbital rhabdomyosarcoma present with a mass in the superonasal quadrant.15,16

The differential diagnosis is that of a childhood progressive rapidly developing mass with or without inflammation: infantile hemangioma, lymphangioma, neuroblastoma, chloroma, cellulitis, and non-specific orbital inflammation.

Imaging

There are no specific radiologic findings in rhabdomyosarcoma.17 Local bone invasion has been reported in 24% of cases,18 with destruction of the orbital wall without orbital expansion seen in 30%.15,19 CT imaging typically shows a homogeneous (92%) well-defined soft tissue mass without bone

destruction that takes up contrast in a moderate to marked amount; rarely the mass is poorly defined as it invades surrounding structures. It is most often extraconal (87%), in the supero-nasal quadrant (66%), (Figures 12.1A and B) and may displace but does not appear to arise from the extraocular muscles.15,16,20 Invasion of the sinus is noted in 20%.15 Focal hemorrhage or necrosis may result in heterogeneity.17 MRI typically shows isointensity to skeletal muscle and hypointensity to orbital fat on T1, hyperintensity on T2 to orbital fat and muscle, decreased signal intensity on all pulse sequences, and moderate to marked uptake of gadolinium.16,17,20

Classification

The International Classification of Rhabdomyosarcoma combined previous histologic classification schemes to provide a system based on prognosis.12 The Pleomorphic subtype was excluded from this classification system because of its rarity in children (Table 1). The WHO classification has divided rhabdomyosarcoma into embryonal, alveolar, and pleomorphic subtypes. The spindle cell and botryoid are considered variants of the embryonal subtype.21 The alveolar subtype more commonly presents in the inferior orbit.

Management

Before the 1960’s rhabdomyosarcoma was an almost uniformly fatal disease. Common metastatic sites

Mesenchymal Tumors 171

included the lung (66% of metastasis), lymph nodes, and bone marrow.22 Interestingly, lymph node metastasis is highly related to site of origin with lower rates seen in orbital tumors.22 Since the development of combination therapy, including biopsy/ conservative surgery, radiation, and multi-agent chemotherapy, the majority of children are now surviving.14 Survival is related to pre-treatment tumor extension past the site of origin, size, nodal involvement, and metastasis at presentation.6 Anatomic site is related to prognosis with the orbit having the best prognosis (92% survival).5,23,24 Histologic type, as previously mentioned, is also associated with survival.12 (Table 1).

Management begins with pathologic confirmation and staging. Two contrasting clinical philoshophies have emerged from the main clinical trial groups. The American Intergroup Rhabdo-

Table 1: The International classification of

Rhabdomyosarcoma (1995)

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myosarcoma Study Group (IRSG) have tended to be more aggressive by utilizing routine radiotherapy, except for tumors that are totally excised, followed by prolonged chemotherapeutic regimes.25,26 Whereas the European International Society of Pediatric Oncology (SIOP) have attempted to use short course chemotherapy and have avoided surgery or radiotherapy if possible.27-29 The best treatment option is likely somewhere between these two philosophies.30 The vast majority of recurrences occur within 3 years of presentation and can often be treated with chemotherapy and repeat excision. In cases with refractory orbital tumors, salvage surgery has been shown to be beneficial.31

Complications related to treatment include cataract (55-82%), dry eye (30-36%), radiation retinopathy (6%), and bony hypoplasia (24-59%) secondary to radiation induced damage.15,32 Secondary malignancies are rare (1.2-3%) and most commonly occur in patients who have received alkylating agents and radiation.15,33

Rhabdomyoma

Tumors of skeletal muscle differentiation are atypical in that malignant are more common than the benign. Rhabdomyoma is a rare benign tumor that has had only 6 cases described in the orbit.34-38 Extracardiac rhabdomyomas are divided into 4 categories: adult, fetal, genital, and the rhabdomyomatous mesenchymal hamartoma types. The adult and fetal type have a predilection for the head and neck and the rhabdomyomatous mesenchymal hamartoma occurs mainly in the periorbital and perioral subcutaneous tissue in children.14 We have reported the only case of rhabdomyomatous mesenchymal hamartoma reported in the orbit.38 Tumor excision or debulking with observation have been described if symptomatic, since they can regress with time.39 Recurrences are extremely rare and are typically associated with incomplete removal.

Very little has been written about the radiologic findings of extracardiac rhabdomyoma.17 CT imaging demonstrates an ill defined homogeneous lesion that does not show signs of necrosis or hemorrhage with heterogeneous enhancement.37 The adjacent bone can be remodelled secondary to pressure but destruction is absent.37 MRI demonstrates a well defined mass similar to muscle on T1 and T2 weighted images with variable enhancement patterns.37,40-42

Smooth Muscle Tumors

Smooth muscle tumors of the orbit are exceedingly rare and can arise from Muller’s muscle and the smooth muscle overlying the inferior orbital fissure. Leiomyoma is a benign slow growing lesion with three distinct clinical groups: (1) leiomyoma cutis, (2) deep dermal (genital leiomyomas), and

(3) leiomyoma of deep soft tissue (musculoskeletal).14 The most common location for these tumors is the female genital tract.44 About 20 cases in the orbit have been reported with a mean age of presentation in the orbit of 36 years.43 Complete excision is the preferred treatment, since they are not sensitive to radiation, and no orbital recurrences have been found with complete excision.43 Interestingly, regression is commonly seen with leiomyomas in other body sites.14

Leiomyosarcomas are rapidly growing infiltrative malignancies that can vary in their natural behavior. They account for 5-10% of soft tissue sarcomas2,45,46, are more common in females, present at a median age of 60,47 and they can occur in younger individuals who have received radiation therapy.48,49 Most commonly they are retroperitoneal, thus lesions outside this location are poorly understood; yet certain differences have been consistently documented. Extra-peritoneal location seems to have a better prognosis with a 5 year survival of approximately 64% and equal gender incidence.45,50 Although extremely rare in the orbit exenteration is the preferred treatment.51-55 Adjuvant chemotherapy and radiotherapy may be beneficial.56

Imaging of subcutaneous leiomyoma typically show a well-defined mass on MR with T1 intensity similar to skeletal muscle and T2 displaying a heterogeneous high or mixed signal intensity.17 Deep leiomyomas often show calcification, T1 intermediate signal intensity, T2 variable intensity, and marked contrast enhancement.17 Leiomyosarcomas do not display specific features on imaging. Hemorrhage, necrosis, and cystic change are common. A hypervascular mass with arteriovenous shunting is often seen on arteriography.17

Adipose Tumors

Despite fat making up the majority of the orbital volume and lipomas being the most common soft tissue tumor in the body14, tumors arising from adipose tissue in the orbit are rare. Lipomas should