Surgical anatomy:

The orbit in the broadest sense describes the cavity containing structures essential for ocular function and the bony architecture that encases them and resembles a pear, with its widest aperture anterior and narrowing posteriorly. It is an anatomically complex structure containing the globe, extraocular muscles, fat, vascular, nerve, glandular, and connective tissues.

The apex is formed by the optic canal and superior orbital fissure. The roof is made up of the frontal bone. The maxilla and zygoma form the floor. The lateral wall is made up of the zygoma and the greater wing of the sphenoid. The maxilla, the lacrimal bone, and the ethmoid bone contribute to the medial wall.

The optic canal is about 10mm long, 5mm wide, and 5mm in height. It extends anteroinferolaterally at an angle of about 40 degrees to the sagittal plane from the optic foramen. The upper root of the lesser wing of the sphenoid forms the roof of the canal. Medial border is by the sphenoid sinus and the ethmoid air cells. The optic strut, a bone ridge joining the lesser wing to the body of the sphenoid bone, forms the inferior lateral border of the canal. The superior orbital fissure is retort shaped with the broad end placed medially. A fibrous ring, the annulus of Zinn, surrounds the optic canal and the medial dilated part of the superior orbital fissure.

The intracranial archnoid continues as a discrete structure through the optic canal and fuses with the pia at the globe. At the orbital portion of the optic canal, the pia and the archnoid are fused dorsomedially and ventrally with the dura and the fibrous annulus of Zinn. The intracranial dura continues through the canal as a dural-periosteal layer and then separates into the dura of the optic nerve, and the periorbita. At the apex, the six extraocular muscles oigin from the annulus of Zinn. The levator muscle arises from the upper medial margin of the annulus, and the superior rectus, lying immediately beneath the levator, arises from the superior portion of the annulus. Medial rectus is more medial and inferior. The annulus loops widely around the nerve, laterally and inferiorly, giving rise to the lateral rectus which has two heads. The muscles broaden as they pass forward to form a cone.

The annulus of Zinn envelops the optic foramen and the medial aspect of the orbital fissure. The portion of the orbital apex enclosed by the annulus is called the oculomotor foramen. This foramen transmits the superior oculomotor, the inferior oculomotor, the abducens, and the nasociliary nerves. They remain inside the muscle cone. The trochlear, frontal, and lacrimal branches of the 5^th nerve and the superior ophthalmic vein pass through the orbital fissure.

The ophthalmic artery, branches off from the ICA, just above the cavernous sinus. It passes in the optic canal lateral and inferior to the optic nerve. It provides the major supply to the optic nerve. As it enters into the orbit, it becomes more medial, and 8-15 mm behind the globe it gives off the central retinal artery that penetrates into the medial midportion of the optic nerve to supply the retina. The primary venous drainage is through the superior and inferior ophthalmic veins. The intraorbital optic nerve is about 30mm long, 5mm longer than distance from the posterior margin of the globe to the orbital apex.

On unroofing the orbit, the frontalis nerve is visible through the periorbita. On opening the periorbita, the frontalis nerve is seen overlying the levator and superior rectus muscles. In the same plane, lies the trochlear nerve, which crosses from lateral to medial above the optic nerve. The nerve is approached medially between the dorasal superior rectus and the medial rectus muscles. This obviates potential trauma to the nerves passing through the oculomotor foramen. In the orbital apex, the optic nerve is approached laterally so as not to jeopardize its blood supply.

Progressive proptosis is the most common symptom. Apical tumors and those within the muscle cone push the eyeball forwards (axial proptosis). Extraconal tumors displace the eyeball in the opposite direction. A hyperostosing sphenoidal meningioma produces prominence of the lateral wall. Pulsatile exophthalmus in neurofibromatosis suggests a defect in the sphenoid bone. The tumor may be palpated.

Diplopia with limitation of extraocular movements is also common. Commonly, it is be due to mechanical factors. Muscle infiltration or motor nerve palsies may also result in diplopia. The eye can be rotated freely by the examiner in nerve palsies after anesthetizing the conjunctiva.

Progressive visual loss may be the presenting symptom in some. It may be transient and only in certain directions of gaze. The unilateral visual loss may be detected by the patient at a late stage. Testing for color vision may detect an early visual defect.

Pain is not common and is a late manifestation in malignancy. Painful paresis of one or more ocular nerves point to a cavernous sinus lesion.

Chemosis suggest an inflammatory lesion or carotico-cavernous fistula (CCF), and rarely in a malignant lesion. A bruit may suggest a CCF. Intraorbital AV fistula and hemangioma can also produce a bruit.

Pupillay abnormalities due to isolated sympathetic or parasympathetic nerves as they pass through superior orbital fissure are unusual.

Ophthalmoscopic examination will demonstrate either papilledema or optic atrophy. Chronic compression of the central retinal vein redirects retinal blood to the choroids via a pre-existing system resulting in optociliary shunts. A retroocular striae may suggest a lesion deforming the orbit.

MRI is the imaging of choice. It is particularly valuable in assessing the orbital pathway because of the high degree of sensitivity of fat tissue, changes of hydration within the soft tissue, and lack of ionizing radiation. Gadolinium MRI adds to better delineation.

A CT may help t o visualize the bony involvement better. Plain x-rays have become obsolete.

Carotid angiography helps in evaluation of CCF and orbital AV fistula.

Duplex ultrasound is useful to assess the hemodynamic flow in the ophthalmic and retinal arteries.

The management of orbital tumors greatly depends on such factors as tumor type, tumor location, patient age, and vision. However, the following generalizations can be made.

Orbital inflammatory syndrome (orbital pseudotumor) may be amenable to steroid treatment.

If the orbital lesion is discrete, then surgical excision may be curative.  Examples of discrete lesions include cavernous hemangioma, unruptured dermoid cysts, neurofibromas and schwannomas.

If the orbital lesion infiltrates the tissues, complete excision may not be possible without harming the eye.  Examples of infiltrative lesions include lymphoma, lymphangiomas, and orbital metastases.

Depending on the type of tumor, further surgery, radiation, chemotherapy or a combination of the aforementioned treatments may be required.

Vascular orbital tumors composed of large blood vessels are difficult to address surgically because of their tendency to bleed.  Some vascular lesions of the orbit are amenable to embolization with the aid of an interventional radiologist

Restoration of the proptosed eyeball to is normal position with preservation of vision and ocular motor function and cosmesis are the main goals of orbital surgery.

Surgical spaces in the orbit are used to define the location of the lesion.

The three surgical spaces are the subpersiosteal, peripheral surgical and central surgical spaces.

a) The subperiosteal space potentially exists between the orbital wall and the periorbita. Frontal and ethmoidal sinus mucocoels, epithelial tumors arising from sinuses, orbital abscesses, dermoid cysts and metastases begin in the subperiosteal space before encroaching onto the deep orbital structures. b) The peripheral surgical space exists between the periorbita and the extraocular muscles. Lesions involving the peripheral surgical space are lymphangioma, hemangioma, dermoid cyst, lacrimal gland tumors, metastatic lesions or orbital varices. C) The central surgical space is seen posterior to the eye-ball, within the muscle cone. In the central surgical space cavernous hemangioma, hemangio-pericytoma, neurofibroma and pseudotumor are the lesions commonly seen.

The position within the surgical spaces and the character of the lesion determine the specific choice. The surgeon must use clinical and radiographic information to decide on the simplest and safest approach to the orbital lesion. The approach is designed according to the location and nature of the lesion. Those with intracranial extension or involvement of the apex are primarily the responsibility of the neurosurgeon. Those with paranasal extension require skullbase approach ideally. Lesions not involving the apex and wholly within the orbit may be managed by an ophthalmologist or a neurosurgeon.

Three routes are used in orbitotomy: anterior, lateral and superior (transcranial). The orbit may be approached by any route or by a combination of these.

Anterior approach: The majority of orbital procedures can be carried out through an anterior incision in skin or conjunctiva. More commonly, ophthalmic surgeons use this approach. This approach is useful for biopsy of lesions anywhere in the orbit or to remove well-defined anteriorly located tumors. Access can be through conjunctiva or skin. When approached through skin, the dissection may either extraperiosteal or more directly through the orbital septum. The main incision sites are superior, inferior, in quadrants, medial and lateral or directly over a palpable lesion.

There are three anterior approaches: transconjunctival, extraperiosteal and transeptal.

Transconjunctival approach:

Some anterior periocular and intraconal lesions can be approached by direct conunctival incision and dissection. A rectus muscle may be disinserted to enter the intraconal space and the retractors placed between the muscle and the globe. In addition, the optic nerve may accessed by this route where it can be operated upon following disinsertion of the medial rectus muscle, with lateral rotation and anterior distraction of the globe. This is a particularly useful approach to optic nerve sheath decompression for chronic papilledema.

Exraperiosteal approach:

The anterior extraperiosteal approach is most useful for lesions occurring in the peripheral surgical space adjacent to periosteum or arising from and involving bone. In particular, lesions such as dermoid cysts are readily accessible by this approach. The skin incision is usually made just at the orbital rim and carried down to the periosteum, which can then be incised and elevated. The extraperiosteal space can then be safety and extensively explored. An alternative route of access inferiorly can be by means of subsciliary incision through skin and orbicularis muscle with dissection along the plane of the orbital septum and incision of the periosteum at the orbital margin. The entire floor of the orbit can be easily explored.

For the most part, anterior orbitotomies do not require bony resection. But some large superior orbital lesions can be more readily accessed by temporary removal of the superior orbital margin. A clearer view of the entire superior orbital space can be gained this way. It is not necessary to transect the supraorbital nerve when operating on large superior lesions. The nerve can be distracted after unroofing the bony canal or incising the overlying ligament at the time of superior orbital exploration.

Larger explorations through the extraperiosteal space usually require postoperative drainage with a Penrose drain. It should be cautioned that the extraperiosteal approach should not be utilized in biopsy of suspected malignant intraorbital lesions because the periosteum provides a barrier to regress of malignancies.

Trans-septal approach:

Trans-septal route involves entry into the orbit through the orbital septum leaving the periosteum intact. This approach is indicated for biopsy of most unresectable orbital malignancies. Anteriorly placed small tumors can be removed through this route. Incision can be made anywhere along the inferior orbit, but lacrimal sac must be avoided medially. Superior incisions have to avoid the supraorbital and supratrochlear nerves. Skin incision is made over the preseptal orbicularis within the orbital rim. In the lower lid a subciliary incision may be used in younger patients. Orbicularis is opened and separated. Traction sutures are put to promote exposure and hemostasis. After identifying the orbital septum, gentle pressure is applied over the upper lid which produces a forward displacement of the orbital fat and septum. The septum is opened and extended both medially and laterally. Orbital fat is displaced with a malleable retractor to locate the lesion. The trans-septal approach can be accessed through the relaxation lines around the eye.

Lateral approach: In 1889, Krönlein first described the lateral orbitotomy approach. This approach is used less often these days. Lateral orbitotomy provides the best access to reach the posterior lesions both within and outside the muscle cone. Ideally, the lesions lateral to the optic nerve and the apex are dealt with by this approach. The amount of bony excision can be customized to include more or the superolateral orbital rim, and even the zygomatic arch when necessary, depending on the size and location of various lesions. Most retrobulbar and parabulbar lesions can be handled by an anterior or lateral orbitotomy alone or in combination.

The patient is positioned with the head slightly elevated and minimally rotated in the direction opposite the operating side. Two types of incisions are advocated to reach the lateral orbit. The Wright incision (a curvilinear incision, extending from the lateral half of the eyebrow to the zygomatic arch, anterior to the hairline) allows a greater access to the lacrimal gland fossa tumors and lesions in the superior and posterior quadrants. The length of the incision can be adjusted depending on location and extent of the orbital mass. Dissection is carried down to expose the periosteum and temporalis muscle. The Berke incision involves a 3 to 5 cms horizontal incision after a complete lateral canthotomy. The upper and lower limbs of the lateral canthal tendon are dissected completely from the lateral orbital rim.

The periosteum is incised from the superior aspect of the zygomatic arch to the zygomatioco-frontal process. The periosteum and temporalis muscle are reflected posteriorly. Stripping the temporalis muscle from the bony fossa needs blunt dissection. Then the periorbita is elevated from the inner orbital wall. Separation of periorbita from the orbital rim to the apex must be done meticulously. After protecting the globe with a malleable retractor, bony cuts are made using a saw or chisel. Superior bone cut is above the fronto-zygomatic suture and inferior cut is along the upper margin of the zygomatic arch. The bony opening may be enlarged posteriorly to the depth of temporalis fossa with a rongeur or drill.

The periorbita is incised antero-posteriorly and a vertical incision is made to form a ‘T’. Then the lateral rectus is identified and kept aside by gentle traction suture or umbilical tape. On occasions, one may have to do deeper intraconal dissections to expose a tumor mass or to operate on the optic nerve.

For evaluation of the central surgical space, especially if the lesion is small one, gentle traction can be exerted on the suture placed into the stump of the scleral insertion of the lateral rectus muscle. This maneuver pulls the optic nerve into view without direct pressure by the surgeon. The short ciliary arteries are readily seen and should not be torn. It is important to remember that the central retinal artery enters the optic nerve inferiorly about 10 to 15mm behind the globe. If the dural sheath is to be opened, it is well to incise it on its anterolateral surface, well away its vasculature.

Superior approach: The superior approach is necessarily the domain of neurosurgeon. Dandy in 1921 laid the foundation for Neurosurgeon’s role in orbital tumors with transcranial approach. The superior approach indicated in compound trauma of the orbit and intracranial cavity, decompression of the optic canal, or for removal of apical or combined apical intracranial lesions. There are three types of procedures used for this approach: Panoramic orbitotomy (Fronto-orbital temporal approach), Frontal approach, Supraorbital approach.

Fronto-orbital temporal (Panoramic) approach:

This procedure allows for an en bloc excision of the roof and lateral wall of the orbit and a wide view of both the orbit and adjacent intracranial structure. This approach consists of a coronal incision and removal of the frontal flap in the usual manner followed by dissection of the temporalis fossa and elevation of periorbita from the adjacent bone. An incision is then made along the superomedial wall of the orbit after distracting the frontal lobe from above. The bony incision is extended along the roof of the orbit to the lateral margin near the apex, whence the lateral wall and frontozygomatic process are incised. With removal of the bone a wide view of the roof and lateral orbital structures is obtained. This approach is particularly useful for excision of tumors at the apex of the orbit or for combined intracranial orbital lesions such as tumor of the optic nerve or sphenoid wing.

Frontal approach:

With the patient in the supine position a bicoronal skin incision is made. A four burrhole frontal bone flap is elevated after a subperiosteal dissection down to orbital rim. If the tumour is confined to the orbit an extradural approach is used. The dura is stripped from the floor of the frontal fossa to expose the orbital roof. Orbital unroofing is performed initially with a high-speed drill or a chisel and then rongeurs are used. The optic canal, however, is unroofed not with rongeurs, but only with a high speed diamond drill. The orbitotomy extends medially to within 1.5cm of the midline and laterally to within 1cm of the orbital margin.

When orbital unroofing is complete, the transparent periorbita displays the frontal branch of the fifth nerve overlying the superior rectus and levator muscles. The bony canal must be unroofed and annulus of Zinn incised apically in the orbit. The best site for incision of the annulus is medially between the superior oblique origin and the levator palpebrae-superior rectus origins. The fourth nerve can be seen coursing over these structures to its site of insertion in posterior third of the superior oblique muscle. It may be necessary to transect the fourth nerve in order to deliver and optic nerve tumor. However, this can be avoided by carefully dissecting the optic nerve within its dural sheath from the annulus, transecting it intracranially, and pulling it forward through the annulus into the orbit, from which it can be removed following transection at the globe and dissection from adjacent structures. Meningiomas or optic gliomas are best approached by retracting the superior rectus and levator muscles laterally. Dissection through the fat is performed with small retractors and cottonoids. It is possible to dissect the posterior ciliary nerves and vessels within the orbit and avoid sectioning them while doing this procedure. After excision of the tumor the orbital roof is reconstructed with stainless steel mesh or bone taken from the inner surface of the bone flap.

Supraorbital approach:

This approach ensures best exposure of the apical portion of the orbit, with minimal or no retraction of the frontal lobe. A bicoronal skin incision is used and the scalp, including the periosteum, reflected anteriorly. At the superior orbital ridge, the periorbita, which is continuous with the periosteum, is separated from the surface of the orbital roof. Two burrholes are placed, one in the midline at the level of the orbital ridge and the other just behind the arch of zygomatic process. The two burrholes are then connected superiorly using a craniotomy to create the bone flap. The bone flap so fashioned incorporates the superior orbital rim and part of the orbital roof, thus allowing for an excellent cosmetic closure. A further 3 to 4cms of the orbital roof may then the removed using rongeurs. Minimally extradural retraction of the frontal lobe allows easy access to the superior and posterior orbit.

Combined approach: All of the approaches defined above can be used in combinations or with variations to obtain access to any of the surgical spaces of the orbit. Widening bony incisions and even removing part or all the sinus structures to expand the surgical space may rarely be necessary.

Transient complete or partial lateral and superior rectus palsy occurs in almost all cases. Improvement usually is seen within several days to 3 to 6 weeks and recovery is complete by three months. Ptosis can be prevented by gentle retraction of levator palpebrae superioris; if it occurs, it usually resolves spontaneously. Visual loss can result from injury to the optic nerve or due to central retinal artery occlusion while dissecting medial to the optic nerve in the apex. Perforation of the globe is another potential risk. Postoperative hemorrhage will cause increasing proptosis, ecchymosis, neuropraxia, and pain. The rapidity of onset and development varies depending on the source of bleeding. If the hemorrhage threatens ocular function (as defined by decreasing vision with an afferent papillary defect) or if it causes severe pain, prompt relief of orbital pressure is necessary. CT scan or ultrasonography may help to locate the blood pool. The decompression can be done through the original incision and it may be enhanced if necessary by means of alternate routed as for any decompression.

The most common childhood tumors are benign and arise from cystic orbital structures (dermoids) or abnormal blood vessels within the orbit (hemangioma).

Capillary Hemangiomas: Capillary hemangiomas of the orbit are benign vascular tumors, and are found almost exclusively in children. They are the most common orbital tumors found in children. Lined by vascular endothelium and pericytes, these histologic benign lesions manifest at birth or within the first 3 months of life, enlarge rapidly, and begin to commence contracting around age 1 year. About 70% of these tumors spontaneously decrease in size by seven years of age.  There are usually no other associated systemic conditions. CT shows a large hyperdense, lobulated enhancing mass. Total excision is impossible. The necessity of treatment depends on whether there are ocular complications, such as the development of amblyopia (lazy eye) or strabismus (crossed eye).  Most orbital capillary hemangiomas that cause secondary ocular complications can be treated with steroids that are either administered systemically, or injected into the tumor. The prognosis is generally good.

Dermoid and Epidermoid Cysts: Dermoid and epidermoid cysts are benign cystic structures which may be present in the orbit, upper eyelid, or brow. They constitute 5% of the orbital tumors. They often progress very slowly. CT shows a well circumscribed low density lesion. Most are treated with surgical excision and the prognosis is good. Total excision may be difficult.

Optic Nerve Glioma: (discussed elsewhere)
 

Rhabdomyosarcoma: Rhabdomyosarcoma, a mesenchymal tumor, is the most common malignant orbital tumor of childhood. These devastating lesions usually occur in children younger than age 2 years or older than age 6 years, and they have a predilection for the superior nasal orbit. The average age of onset is about 6 years.  This type of tumor generally grow very rapidly, causing proptosis (forward displacement) of the eye.  It may destroy bone and enter adjacent sinuses.  CT reveals a solid homogeneously enhancing tumor. A biopsy is required to confirm the diagnosis, but the tumor cannot usually be removed surgically because of its infiltrative nature.  Once the diagnosis is made, the child is treated promptly with radiation and chemotherapy.

Other malignant lesions include Burkitt lymphoma and granulocytic sarcoma.

Metastatic tumors: Neuroblastomas, Ewing sarcoma, Wilms tumor, and leukemias are the more common metastatic orbital lesions afflicting children. Metastatic neuroblastoma is an orbital tumor that may occur in children with an adrenal gland tumor (neuroblastoma). In fact, 95% of patients who present with this orbital tumor have a known history of adrenal gland tumor.  These children may present with proptosis of one or both eyes and conjunctival or eyelid hemorrhage. These tumors are usually treated with combined radiation and chemotherapy.

Orbital tumors in adults:

Cavernous hemangiomas: They are the most common benign orbital tumor. They are well capsulated. Histologically, large blood-filled, endothelial-lined spaces with fibrous interstitial tissue and smooth muscle are discerned. CT reveals a well outlined hyperdense lesion with minimal enhancement. Phleboliths (calcifications) may be seen. It is isointense in ion with minimal enhancement. Phleboliths (calcifications) may be seen. It is isointense in T1 MRI and significantly hyperintense to fat on T2. These lesions usually are well tolerated by the patient and managed by conservative therapy and reassurance, unless visual acuity or field loss is found. Total excision is possible. Meningioma: They arise from optic nerve dural sheath or periorbita. Sheath meningiomas (5-6% of all orbital meningiomas) arise from meningothelial cells present in the meninges covering the optic nerve. Middle aged females are more frequently involved. More commonly, they arise within the intraorbital optic nerve sheath than within the canal. Optic nerve sheath meningioma is the most common orbital apical tumor and is the most common orbital tumor with intracranial extension. (However, it is more common for an intracranial meningioma to extend into orbit. Fibrous dysplasia, giant aneurysms, and encephalocoeles can also extend into the orbit). More often, they originate at the cranial end of the optic canal between the optic nerve and carotid artery and secondarily extend into the orbit. The tumor may grow extradurally, resulting in early proptosis or subdurally, resulting in early visual loss and papilledema; proptosis occurs at a later stage. In combined intra and extradural types there is progressive visual loss with proptosis. Some of them are bilateral. Lesions near the optic foramen or the optic canal produce sclerosis of the bone or widening of the optic canal and they may be seen in a plain x-ray. Sclerosis of the optic foramen in a skull x-ray rules out a glioma. CT and MRI delineate the tumor from the optic nerve. The treatment is controversial as the tumor is slow growing and the natural history is variable. Radical excision will invariably cause loss of vision and is better delayed until significant visual compromise. Excision of the tumor involving the apex will also result in a frozen eye. Subtotal excision and radiotherapy may be an acceptable alternative.

Periorbital meningioma-CT   Optic sheath meningioma-CT       Optic nerve glioma-CT   Cavernous Hemangioma -CT   Schwannoma with intra-cavernous extension-MRI            Cysticercosis-CT   Rhabdomyosarcoma-CT           Lymphangioma-CT

In the younger patients, these tumors are aggressive and radical excision may be justified.

Periorbital meningiomas arise from the archnoid cells in the superior orbital fissure and involve the upper lateral quadrant of the orbit. Ectopic archnoidal cells within the perineurium of a peripheral nerve have been postulated as another source. Those involving the superior orbital fissure can not be removed without damaging the nerves passing through the fissure; subtotal excision and radiotherapy will be more acceptable.

Lymphoma: It accounts for about 10% of all orbital tumors, usually as a manifestation of systemic disease. It can occur anywhere in the orbit and may mimic a pseudo tumor. Circumscribed forms usually involve the lacrimal gland and the diffuse form affects the muscle cone. There may be bone destruction. CT shows variable morphology. On MRI it is hypo intense with gadolinium enhancement.

Pseudotumor: It is a localized inflammatory disease that mimics a tumor. There is no associated local or systemic cause. The patient usually presents with rapidly progressing, painful proptosis. They may be self limiting with or without visual impairment. Recurrences are common. It is usually unilateral. Bilateral ones must be differentiated from Grave’s disease, or systemic collagen disease. CT reveals multifocal involvement around tenon’s capsule, thickening of extraocular muscles, and enlarged lacrimal gland. MRI shows nonspecific widespread involvement. Occasionally, the diagnosis is by a biopsy. 40-60 mg/day of prednisolone over weeks to months is the usual treatment.

Hemangiopericytoma: It is from the pericyte of a capillary and usually well encapsulated. Occasionally it is infiltrative. The patient presents with slow painless proptosis.

Lacrimal gland tumor: 5% of the orbital tumors are the epithelial tumors of the lacrimal gland. Majority of them are inflammatory. 50% of neoplastic ones are mixed ones (painless proptosis) and the other 50% are carcinomas, mainly, adenoid cystic carcinoma (painful proptosis). CT shows a mass in the superotemporal quadrant. A period of conservative therapy with anti-inflammatory drugs is indicated when inflammatory swelling is suspected. Progressing lesion or the presence of bony involvement warrants an en bloc excision. Radical excision may be considered in malignancy.

Benign nerve sheath tumor: It could be neurofibroma, schwannoma, or malignant sneurilemmoma. And may or may not be associated with neurofibromatosis. They occur commonly in the superolateral compartment and present with proptosis, more marked in schwannomas than in neurofibromas. Total excision is possible; however, total excision is impossible with plexiform neurofibroma.

Mucocoeles: They are a common cause of proptosis. They result from expansion of the sinuses secondary to blockage. Pyococele results when infected. A smooth bulge in the bony wall of the ethmoid or frontal sinus is characteristic. Complete removal including the sinus mucosa and restoration of drainage is essential.

Lymphangioma: It is slow growing tumor that infiltrates the orbital tissue. Spontaneous intratumoral hemorrhage can produce episodic proptosis. Total excision is impossible.

Fibrous histiocytoma: This is the most common mesenchymal orbital tumor. It is a benign, slow growing, unencapsulated infiltrative tumor of the orbit, and may become malignant. CT reveals a high density mass. Total excision is advised.

Dermoid cyst, optic nerve glioma, granuloma, and sarcomas are other benign orbital tumors in adults.

Metastatases: It is the most common malignant tumor of the orbit. In adults, carcinomas of breast and the lung are the most common source. Though proptosis is common, schirrous carcinoma of the breast may produce retraction of the globe. CT morphology is variable.