Orbital Neoplasia

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Chapter 7

Orbital Neoplasia

A wide variety of primary and secondary neoplasms may affect the orbit. Most orbital masses are benign and slow growing; however, approximately 20% are malignant. As is often the case in pediatrics, obtaining a precise history and conducting a physical examination may be challenging. Presenting symptoms of different entities may overlap considerably; for example, leukocoria, a worrisome sign of retinoblastoma, also can be a manifestation of infectious/inflammatory or developmental conditions masquerading as retinoblastoma. Imaging findings also may overlap; for example, some forms of orbital rhabdomyosarcoma (RMS) initially may present as inflammatory cellulitis or may closely resemble a hemangioma based on imaging features. Some non-neoplastic orbital masses may present quite dramatically with visual loss and destructive changes of the orbit (e.g., Wegener granulomatosis and Langerhans cell histiocytosis [LCH]) and must be differentiated from a malignancy. Pertinent clinical information, such as patient age and duration of symptoms, may be of added value when trying to narrow the diagnostic possibilities. The location of the lesion within the orbit may be a clue to its underlying nature because different lesions have the propensity to originate from specific compartments of the orbit. Knowledge of the rate of growth of the mass also may help narrow the differential diagnosis. Rapid progression is suggestive of more aggressive lesions such as RMS, acute leukemic infiltration, or LCH (one of the great mimickers of malignant bone diseases in children). A more indolent course, with little to no progression in visible growth, can be observed in lesions such as dermoid cysts, optic nerve gliomas, or meningiomas.

A precise and timely diagnosis of an orbital mass may be crucial for successful treatment of many disorders and may lead to improved quality of life, preserved vision, or prevention of blindness. Imaging plays an important role in the accurate diagnosis of orbital masses, and at times more than one imaging modality may be required. The primary imaging modalities used to evaluate orbital masses are ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). Ultrasound eye examination is performed with use of a linear, or three-dimensional high-frequency transducer with a small footprint, which is placed over the closed eyelids. It is an effective imaging tool for the evaluation of the globe, papilledema, retinal detachment, and the proximal optic nerve. Color Doppler allows evaluation of the vascularity of intraocular lesions. Orbital ultrasound may be used as a primary imaging tool in the evaluation of young children with leukocoria and for confirmation of papilledema and retinal detachment. However, it is suboptimal for the assessment of extraocular lesions.

CT is excellent at depicting ocular calcifications and evaluating potential orbital bony involvement. It is an easily accessible test and may be used in the primary evaluation of acute proptosis. Modern CT equipment allows for the acquisition of high-resolution images in the axial plane with additional computed reconstruction images in the coronal and/or sagittal planes, thus avoiding the need for direct acquisition of images in orthogonal planes and thereby preventing additional radiation exposure. The speed of current CT scanners may allow the imaging team to avoid patient sedation in many cases.

Orbital masses are optimally imaged with MRI. The use of high-resolution, 2- to 3-mm thick T1-weighted and T2-weighted sequences, as well as thin-slice postgadolinium multiplanar sequences, are mandatory for precision imaging of orbital structures. Fat suppression often is essential in orbital imaging to allow for tissue differentiation and distinction from intraorbital fat, as well as in the assessment of the marrow within the bony orbit and of pathologically enhancing tissues. Diffusion-weighted imaging (DWI) plays an important role in further characterizing the tissues within and around tumors. Apparent diffusion coefficient mapping may help in the differentiation of benign and malignant lesions and occasionally may allow for assessment of treatment response. Half-Fourier acquisition single-shot turbo or fast spin-echo imaging is helpful for depiction of cystic components of orbital mass and for better visualization of sinus tracts.

Use of a high-resolution matrix, a small field of view, and routine use of fat-saturation techniques, as well as the administration of intravenous (IV) contrast (gadolinium), are all necessary components in successfully imaging orbital pathology. When analyzing images, particular attention should be given to the presence of bone erosion, the avidity of contrast uptake, and lesion vascularity, as well as the presence of intracranial extension. Tumor extension through the orbital fissures is better delineated on MRI, whereas erosive bony changes are better depicted on CT. CT and MR are complimentary imaging techniques in the evaluation of orbital tumors, and in some cases, both may be indicated for proper and complete evaluation of complex orbital masses, both before treatment and when assessing for potential residual or recurrent disease. Most protocols for imaging of orbital tumors include brain imaging for the evaluation of potential intracranial extension.

Certain orbital tumors may be a manifestation of more complex or systemic conditions or syndromes and may thus require further evaluation of extraorbital regions for involvement of other organ systems. Examples of known associations of orbital lesions potentially involving other organ systems are (1) hemangiomata associated with PHACES syndrome (posterior fossa abnormalities, hemangiomas of the cervical facial region, arterial anomalies, cardiac defects, eye anomalies, and sternal defects) and (2) kaposiform hemangioendotheliomas and their association with Kasabach-Merritt syndrome, a severe, life-threatening consumptive coagulopathy.

Although analysis of imaging findings along with clinical signs and symptoms may lead to a narrowed differential diagnosis, the definitive diagnosis almost always is based on histopathologic findings.

The following discussion of imaging of orbital pathology is divided into four categories: ocular lesions, optic nerve sheath lesions, primary orbital lesions, and lesions that secondarily involve the orbit.

Ocular Lesions

Retinoblastoma

Retinoblastoma, which is the most common intraocular pediatric tumor, typically affects children younger than 4 years. Even though retinoblastoma is considered a congenital type of malignant tumor, it is rarely recognized neonatally. Two forms of retinoblastoma—hereditary and sporadic—are described. These forms differ in their clinical presentation and prognosis.

Hereditary retinoblastoma is usually bilateral and multifocal and clinically presents at an earlier age (mean, 6 months). It is associated with a germline mutation in the tumor suppression RB1 gene, located on chromosome 13q14. In a small percentage of patients with heritable retinoblastoma (3% to 7%), intracranial neuroectodermal pineal or suprasellar tumors, termed trilateral retinoblastoma, will develop. Trilateral tumors usually present months after the initial discovery of the ocular lesions and have an associated dismal prognosis. Patients with hereditary RB1 mutations have increased risk (progressive throughout their lifetime) of the development of other malignancies; such malignancies especially develop in patients who have undergone radiation therapy. Secondary tumors that develop most often include osteogenic and other soft tissue sarcomas, leukemia, and malignant melanoma. Secondary nonocular tumors are the leading cause of death in these patients, rather than the primary retinoblastoma itself.

Sporadic retinoblastoma is usually solitary and unilateral and is associated with spontaneous somatic mutations of the RB1 gene. The average age at presentation varies from 13 to 18 months. Patients with sporadic noninvasive intraocular tumors have an excellent prognosis, with a survival rate approaching 90%.

Approximately two thirds of all retinoblastoma cases are unilateral, and one third are bilateral. Several classification systems have been developed for intraocular retinoblastoma, all of which are based on expected results of therapy and predicted salvage of the globe. The rapid evolution of newer retinoblastoma treatment has resulted in the replacement of the previously widely accepted Reese-Ellsworth classification, which is based on intraocular tumor staging and is used in tumor management after external beam radiation. A new International Classification of Retinoblastoma is based mainly on the natural history of retinoblastoma (early disease [group A] to late disease [group E]) and upon the extent of tumor seeding within the vitreous and subretinal space (Box 7-1). This classification is more applicable for patients treated with chemotherapy.

Box 7-1   International Classification of Retinoblastoma

The International Classification of Retinoblastoma is a new classification system for retinoblastoma that is based on tumor size, location, and associated seeding. This new classification system is designed to simplify grouping and assist in predicting treatment outcomes.

For purposes of disease prognostication, it is important to assess tumor growth pattern, which is described according to the retinal spread of tumor. Endophytic tumors grow anteriorly into the vitreous, whereas exophytic tumors grow into subretinal space and tend to have earlier choroidal involvement and increased risk of metastatic spread. Optic nerve involvement is a marker for aggressive and advanced tumors and is associated with a high risk of metastatic disease and consequent increased mortality rates. The most uncommon pattern of spread is that of diffuse infiltrative tumor growth within the retina, which is not characterized by the presence of a nodular mass or by intralesional calcifications. This type of retinoblastoma presents at a later age, with the clinical symptoms sometimes mimicking an inflammatory process.

Leukocoria (or white pupillary reflex) is the most common presenting sign of retinoblastoma. For tumors located in the posterior globe, leukocoria may indicate advanced disease because a lesion in the posterior retina must be sufficiently large to produce leukocoria. Strabismus is the second major presenting sign of retinoblastoma. In contrast to leukocoria, tumors presenting with strabismus as their initial sign are associated with a higher survival rate and a higher chance of salvage of the globe. Patients with exophytic tumor growth may present with retinal detachment surrounding the tumor, indicating tumor extension into the subretinal space.

Leukocoria in a young child that is confirmed by an ophthalmoscopic examination requires further evaluation. Imaging may reliably distinguish retinoblastoma from a host of other conditions that also may present with leukocoria (e.g., persistent hyperplastic primary vitreous, Toxascaris infection, Coats disease, and medulloepithelioma). In many retinoblastoma centers, eye ultrasonography has replaced orbital CT for initial disease assessment. Three-dimensional high-frequency ultrasound is sufficient for assessment of tumor and calcifications but is less suitable for the evaluation of extraocular spread. Retinoblastoma is readily visible on ultrasound as an echogenic irregular retinal mass with focal acoustic shadows. CT is an excellent tool for depicting ocular calcifications (Fig. 7-1, A), but its use in retinoblastoma evaluation has markedly decreased because of the associated radiation risks. MRI has become a relatively quick and convenient modality for the evaluation of retinoblastoma. A variety of tailored MR sequences are beneficial in illustrating the different features of these masses. Specifically, intraocular hemorrhages and calcifications are depicted best on gradient sequences, whereas the malignant, markedly cellular nature of these tumors (composed of immature retinoblasts) is confirmed on T2-weighted and DWI sequences (Fig. 7-1, B and C). Contrast-enhanced sequences provide important information that may affect prognosis and treatment options with respect to tumor spread into the optic nerve (Fig. 7-1, D), anterior chamber, or other adjacent orbital structures. In addition, MRI serves as a surveillance examination of the brain when monitoring for possible leptomeningeal spread of tumor or for the presence of retinoblastoma in more remote locations.

Standard treatment for retinoblastoma has evolved in the past several decades from prior methods of surgical enucleation or external radiation. Most retinoblastoma referral centers are now using alternative therapies that are aimed at eye salvage and avoiding the risks inherent with radiation. These methods include systemic chemotherapy (chemoreduction) along with focal treatments (eye-sparing radiotherapy [local plaque radiation], laser photocoagulation, and cryotherapy) as the primary treatment modality, especially when tumors are small. Orbital imaging is therefore an essential step in deciding the appropriate treatment.

Medulloepithelioma

A medulloepithelioma is another pediatric malignant intraocular tumor that may present with leukocoria. This tumor is a rare embryonal type of neoplasm arising from the nonpigmented epithelial lining of the ciliary body. Patients usually are diagnosed in the first decade of life (at a mean age of 6 years); only rarely is medulloepithelioma seen in adults. Many imaging features of medulloepithelioma may closely resemble those of a retinoblastoma, such as presentation with a nodular enhancing intraocular mass, which occasionally will have calcifications (Fig. 7-2). A medulloepithelioma differs from a retinoblastoma mainly by its anterior location, but it may appear identical to a retinoblastoma when it is located in the vicinity of the optic nerve. Medulloepitheliomas have been divided into two types, teratoid and nonteratoid (diktyoma), based on their histologies. More complex teratoid medulloepitheliomas are composed of heteroplastic elements, including cartilage, which may have associated calcifications, whereas the nonteratoid diktyoma presents as a well-defined, noncalcified mass with associated diffuse contrast enhancement.

Hereditary Orbital Hamartomatosis

Many neurocutaneous disorders (phakomatoses) may have typical ocular masses that may or may not be visible with modern imaging techniques. These lesions represent hereditary hamartomas, which are composed of tissues with limited capacity for proliferation. Examples of these entities may be seen in the settings of tuberous sclerosis, neurofibromatosis (NF), and von Hippel-Lindau disease.

Ocular manifestations of tuberous sclerosis include astrocytic hamartomas of the retina and optic disk. These lesions have a typical appearance on ophthalmologic examination; however, they may calcify as the patient ages and may in fact resemble drusen when located on the optic disk. On thin-section high-resolution T2-weighted imaging, hamartomas of tuberous sclerosis are visible as small hypointense nodules within the posterior globe (e-Fig. 7-3).

Ocular stigmata of NF may present as neuronal hamartomas of the iris, called Lisch nodules, which only occur with NF type 1. Lisch nodules can only rarely be visualized with imaging.

Persons with Sturge-Weber syndrome and von Hippel-Lindau disease may have ocular vascular lesions. Choroidal vascular lesions in persons with Sturge-Weber syndrome may be diffuse or localized and can simulate melanoma on ophthalmoscopic examination, but they may be differentiated from one another on MRI examination. Choroidal vascular lesions demonstrate a typical hyperintense signal on T1-weighted and T2-weighted sequences, which is opposite to the signal characteristics expected with melanoma (a bright T1-weighted signal and a hypointense T2-weighted signal). Ocular manifestations of von Hippel-Lindau disease consist of retinal angiomatosis, which may cause severe complications, including retinal detachment and ocular destruction, and usually present later in childhood or in early adulthood (in the second and third decades of life).

Drusen

Disc drusen are nonhamartomatous subretinal lesions without astrocytic hyperplasia that are associated with the presence of intrapapillary, partially calcified hyaline bodies that form concretions of unknown nature. Drusen likely are the most common etiology for congenital bilateral elevation of the optic nerve discs. Drusen may be detected on funduscopic evaluation or may be seen as an incidental finding on imaging. In both scenarios, it is important to establish the benign nature of disk elevation so as not to confuse drusen (which cause pseudopapilledema) with true papilledema. Equivocal results of ophthalmoscopic examination may lead to orbital imaging, which will either confirm the presence of disc drusen or detect the source of the increased intracranial pressure. Drusen may be diagnosed with use of ultrasound, appearing as foci of increased echogenicity, or drusen can be seen on noncontrast CT most often as bilateral punctuate calcifications within the optic nerve heads (e-Fig. 7-4). MRI demonstrates isolated mild protrusion of the optic discs into the vitreous without perioptic cerebrospinal fluid space enlargement or other imaging features of papilledema. Clinically, drusen are usually asymptomatic and only rarely may be associated with slowly progressive visual loss.

Optic Nerve-Sheath Complex Tumors

Optic nerve-sheath complex lesions include neoplasms of the optic nerves (gliomata), optic nerve sheaths (meningiomas), or rare cases of intraconal peripheral primitive neuroectodermal tumors (PNETs).

Optic Nerve Glioma

Optic nerve glioma (ONG) is the most common primary neoplasm of the optic nerve in children. ONG may be seen in the setting of NF type 1 (Fig. 7-5, A) or may present as an isolated tumor (nonsyndromic) (Fig. 7-5, B). ONGs, which are associated with NF, most often are bilateral lesions that may involve the nerve and surrounding subarachnoid space and are remarkable for their low-grade nature and favorable prognosis. Nonsyndromic ONGs are usually unilateral and histologically are either pilocytic or fibrillary astrocytomas. The mortality rate for these tumors is approximately 5% when the tumor involves only the optic nerve, but hypothalamic involvement portends a more ominous prognosis; despite their benign histology, some series report mortality rates approaching 50%.

Orbital Meningioma

Orbital meningioma is not a common pediatric tumor but has been reported in patients in the first decade of life. Meningiomas of the orbits may be perioptic (e-Fig. 7-6, A-C), arising from the optic nerve sheath, or may extend through the optic canal from an intracranial origin, that is, arising from the area of anterior clinoid process of the sphenoid bone or from the tuberculum sella, with extension anteriorly into the orbit (e-Fig. 7-6, D).

Perineural meningioma is the most common form seen in children, possibly because of early presentation with visual symptoms. Pediatric meningiomas are much more aggressive than the adult form. These tumors may occur as isolated neoplasms or in the setting of NF type 2.

In general, CT is useful in the detection of the orbital portion of some meningiomas but not in differentiating whether the tumor originates from the optic nerve itself or from the optic nerve sheath. These tumors are usually hyperattenuating on CT, often with calcifications (but not in the early stages), seen as the so-called “rail road track sign,” which implies that the surrounding tumor of the nerve sheath is enhancing, not the optic nerve itself. Meningiomas ideally should be imaged with MRI. They most often appear hypointense on T1-weighted and T2-weighted sequences and exhibit avid gadolinium enhancement and restricted diffusion on DWI because of their high cellularity (e-Fig. 7-6, A-C).

Primary optic nerve tumors are not the only cause of optic nerve enlargement. Other causes include non-neoplastic conditions such as inflammatory pseudotumor, optic neuritis, and sarcoid granulomata. Enlargement of the optic nerve-sheath complexes may be caused by true papilledema (related to increased intracranial pressure), perineural hematoma, or granulomatous disease, or it may represent a normal variant.

Primitive Neuroectodermal Tumor

A PNET is a small, round, blue cell malignant tumor of neuroectodermal origin. PNETs that present outside of the central nervous system are referred to as peripheral PNET. It appears that PNET is the least aggressive subtype of tumor among other similar small cell tumors, with a favorable prognosis seen after complete tumor resection. This tumor, similar to Ewing sarcoma, expresses the MIC-2 gene (CD99) on cell membranes, which allows for their differentiation from other tumors. This rare tumor of the orbit presents as an enhancing, heterogeneous, T2-hypointense, intraconal lesion with associated restricted diffusion on DWI (Fig. 7-7, A-C). DWI characteristics are important imaging features that favor a highly cellular lesion, which includes PNET within the limited differential diagnosis. Treatment usually includes globe enucleation, high-dose chemotherapy, and stem cell transplantation.

Orbital Lesions

Vascular Lesions

Vascular orbital mass lesions constitute a heterogeneous group of both true neoplasms and non-neoplastic vascular malformations. Orbital vascular masses occur on a spectrum, ranging from benign lesions such as the common infantile hemangioma (true neoplasm), congenital lesions such as venolymphatic malformations, orbital varices, and arterial-venous malformations, to the rarer locally aggressive lesion known as kaposiform hemangioendothelioma. Mulliken and Glowacki have classified this spectrum of vascular masses based on differing therapeutic approaches for different lesions. Much controversy still exists regarding the nomenclature and classification of these entities. The most common accepted view is that they belong to a spectrum of vascular lesions. Vascular malformations are congenital lesions but usually are clinically occult at birth and tend to present later in life, at times after an upper respiratory tract infection or as a result of spontaneous hemorrhage. In contradistinction, infantile hemangiomas become clinically apparent shortly after birth, and some of the rarer orbital vascular tumors may even be diagnosed prenatally. Imaging protocols also should include evaluation of the brain because of the association of orbital vascular lesions with intracranial vascular anomalies.

Orbital Hemangioma

Orbital hemangiomas are not uncommon lesions and are classified as benign infantile hemangiomas. Orbital hemangiomas usually appear shortly after birth, although up to 40% may be visible at birth only as a faint cutaneous (birth) mark. During the proliferative phase of growth they will become raised, bulky, and compressible. In rare instances, the proliferative phase may be biphasic. The most variable attribute of these lesions is the stage of involution, which may occur over a period of years and results in involution and fatty replacement, without the presence of calcifications. Even after resolution, some persistent fibrofatty mass or abnormal cutaneous pigmentation may remain, mainly leading to cosmetic and aesthetic concerns rather than functional issues.

Only a small percentage of hemangiomas lead to complications, such as ulcerations and bleeding. However, because of their location, early age at presentation, and potential for very rapid growth, orbital hemangiomas may lead to devastating visual impairment as a result of obscuration of light delivery to the eye, especially if the eyelids are involved. Lack of visual input early in life prevents the formation of neural pathways necessary for proper vision later in life and will lead to amblyopia and blindness.

These lobulated lesions often appear bright on T2-weighted imaging, avidly take up gadolinium, and may have multiple flow voids and increased vascularity seen on perfusion imaging (Fig. 7-8, A-C). Although usually nonsyndromic, some hemangiomas are known to occur in conjunction with other systemic abnormalities, such as PHACES (posterior fossa abnormalities, hemangiomas of the cervical facial region, arterial anomalies, cardiac defects, eye anomalies, and sternal defects) (e-Fig. 7-9).

The imaging differential diagnosis for hemangioma includes RMS, vascular malformation, infantile fibromatosis, and infantile fibrosarcoma. The vascular features of hemangioma, particularly the flow voids on MR images, help to distinguish hemangiomas from these other lesions. RMS may be very vascular and contain flow voids but typically occurs in an older age group and often will demonstrate restricted diffusion on DWI. Most hemangiomas are managed conservatively because they tend to resolve on their own. However, tumors that can or do compromise vision are aggressively treated. Therapeutic options include propranolol, systemic or intralesional corticosteroids, α-2a or α-2b interferon, and laser therapy or surgery.

Venolymphatic Malformation

Venolymphatic malformations encompass a group of vascular lesions consisting of vascular channels of varying sizes and histologic types. Most lesions are composed of a combination of anomalous lymphatic and venous vessels. Some lesions consist primarily of lymphatic vessels and are called lymphangiomas or lymphatic malformations, whereas others are composed mainly of venous channels and thus are called venous malformations (formerly known as cavernous hemangiomas). However, most lesions contain both types of vessels, and their clinical presentation and imaging appearances depend on the prevalence of lymphatic or venous components within the individual lesion.

Rootman et al classified combined orbital venolymphatic malformations on the basis of anatomic location into three groups: superficial, deep, or combined lesions. The superficial lesions (and the superficial components of combined lesions) contain lymphatic components at pathologic evaluation. In contrast, deep lesions, as well as the deep component of combined lesions, are predominantly or completely venous in nature, reflecting the distribution of vessels within the normal orbit. When these lesions are superficial, they will involve the eyelid and/or conjunctiva, and they tend to manifest clinically at an early age. Deep lesions in the retrobulbar orbit, although present from birth, may present later in life and even into young adulthood. Unlike hemangiomas, venolymphatic malformations grow with the patient, and they never involute spontaneously. Clinically, these lesions usually present with progressive or acute painless proptosis, but they may present with restricted movement of the extraocular muscles. Intermittent change in size may occur as a result of recurrent hemorrhage, secondary to fragile vessels within the intervening connective tissue septations.

Imaging features may reflect the dual nature of these vascular malformations, with multicystic lymphatic components often containing blood-fluid levels and enhancing solid venous components, which may contain phleboliths. Uncomplicated lymphatic malformations usually do not demonstrate contrast enhancement, or at most may show some peripheral enhancement of the septations. On ultrasound, lymphangiomas exhibit no Doppler flow and demonstrate cystic spaces filled with blood and fluid. On CT their appearance may be inconclusive, not fully reflecting the internal complexity of the lesion (Fig. 7-10, A), but they can appear as a soft tissue mass with associated proptosis. MRI is capable of fully evaluating their true nature and distinguishing them from masses such as RMS lesions (Fig. 7-10, B).

Treatment of orbital vascular lesions remains challenging. In the past it consisted of conservative management if the patient’s vision was not jeopardized. Surgical excision often is difficult and associated with numerous complications, as well as with a high rate of recurrence. Intralesional sclerosing therapy appears to be an effective method for debulking low-flow malformations and is not associated with vision-threatening complications, and thus it is an attractive alternative to surgical resection.

Orbital Varix

Primary congenital venous varices (uncommonly affecting children) represent distensible venous malformations in the retrobulbar compartment of the orbit (e-Fig. 7-11), which may enlarge with dependent posture. The varix may consist of marked enlargement of a single orbital vein or may present as a tangled multivascular mass. Clinically these lesions may present with globe displacement that may augment and increase in conspicuity when the Valsalva maneuver is performed, but at times the lesions are collapsed and may be undetectable. Occasionally these lesions may lead to spontaneous orbital hemorrhage. Secondary varices may occur in the setting of intracranial dural venous thrombosis or arteriovenous shunting.

Nonvascular Lesions

Orbital Tumors

Congenital orbital tumors mostly consist of benign tumors such as teratomas or the more aggressive kaposiform hemangioendotheliomas; however, more aggressive malignant tumors such as angiosarcomas and rhabdoid tumors also occur. The most common malignant orbital tumor in children is rhabdomyosarcoma.

Orbital Teratoma: Orbital teratoma is a very rare congenital tumor that often is diagnosed prenatally with ultrasound and fetal MRI (Fig. 7-12). These tumors usually present as a large heterogeneous mass containing multiple tissue types, including fat, calcium, and bone. Teratomas of the orbit are most often benign and well differentiated; however, they may lead to significant proptosis when located at the orbital apex. The imaging appearance of a teratoma is quite distinctive, with the presence of a very large multicystic mass that includes a solid component and calcification. The solid components may exhibit enhancement after administration of a contrast agent. The enhancement pattern may help to distinguish a teratoma from a dermoid cyst, which, when present, tends to have peripheral enhancement.

A kaposiform hemangioendothelioma may be very large and may sequester platelets, thereby leading to a consumptive coagulopathy as a result of the Kasabach-Merritt phenomenon. This phenomenon is not known to occur with hemangiomas.

Rhabdoid tumors of the orbital region occur in young children (with a mean age of 15 months at presentation) and can be highly vascular and mimic more benign lesions such as hemangiomas. These rare malignant tumors are highly aggressive and lethal (death occurs within 12 months of presentation). Their dense cellularity can produce restricted diffusion on DWI (e-Fig. 7-13, A and B).

Rhabdomyosarcoma: RMS is the most common malignant soft tissue tumor in childhood. The orbits and paranasal sinuses are the second most common location. The embryonal type is the most common variety of orbital RMS; the alveolar and pleomorphic varieties occur rarely. The mean age at presentation is 6 years.

RMS previously was thought to arise from skeletal muscle but now is generally believed to originate from pluripotential mesenchymal cells that have the capacity to differentiate into skeletal muscle. RMS is an aggressive, fast-growing tumor that most often manifests with rapidly progressive proptosis or globe displacement and should be considered in any child with that clinical presentation. Other common signs and symptoms include conjunctival and palpebral swelling, which may erroneously suggest the clinical diagnosis of orbital cellulitis and may lead to confusion with respect to presentation and imaging appearance.

Most tumors are extraconal in location, but intraconal components also may be present. The most typical location for the common embryonal form is in the superonasal quadrant. The less prevalent alveolar form more often affects the inferior orbit. RMS grows rapidly and behaves aggressively, frequently invading the adjacent bones and soft tissues. However, advanced disease is less often encountered today because of greater awareness of the diagnosis.

Both CT and MR imaging play important roles in the preoperative evaluation, staging, and follow-up of orbital RMS tumors. On T2-weighted imaging, these lesions may appear as hypointense, isointense, and even hyperintense with respect to both extraocular muscles and orbital fat (Fig. 7-14, A and B). Because of the high degree of RMS cellularity, the lesions may be predominantly hypointense on T2-weighted imaging, hyperattenuating on CT, and exhibit restricted diffusion on DWI. On T1-weighted contrast-enhanced images, RMS will have moderate to marked enhancement, and in some cases a component of highly vascular internal tissue may mimic the appearance of a hemangioma. Meticulous attention is required in the assessment of local invasion because RMS may invade the paranasal sinuses, as well as for more remote invasion because RMS can spread to the intracranial space via the orbital fissures and then into cavernous sinuses and even the middle cranial fossa. Favorable prognostic factors include lack of distant metastases, a primary site in the orbit, disease confined to the orbit, gross total surgical resection, a patient age of younger than 10 years, an embryonal histologic type, hyperdiploid deoxyribonucleic acid content, and a tumor size of 5 cm or less. The most important prognostic factor is response to therapy, which is assessed with follow-up imaging.

Advances in chemotherapy and radiotherapy have improved survival rates of patients with orbital RMS. This improved survival rate has allowed observation of the late effects of radiotherapy on both facial growth (e.g., bony hypoplasia of the orbit and facial asymmetry) and visual function (e.g., cataract, keratopathy, and retinopathy).

Lesions that Secondarily Involve the Orbit

Metastatic Lesions Involving the Orbits

Orbital metastases are less common in children than in adults. Primary tumors that can metastasize to the bony orbit are neuroblastoma, lymphoma and leukemia, and very rarely Wilms tumor and Ewing sarcoma. Ocular choroid metastases, which are quite common in adults, are exceedingly rare in children.

Neuroblastoma

Neuroblastoma is the most common metastatic tumor of young pediatric patients (Figs. 7-15 and 7-16). In 8% of cases, neuroblastoma first presents with acute orbital symptoms related to tumoral hemorrhage, sudden proptosis, and ecchymosis (raccoon eyes). Neuroblastoma metastases to the head and neck favors the bony skull base and the cranial sutures, at times leading to sutural diastasis on conventional radiographs, with the additional extraaxial soft tissue masses only discernable on cross-sectional CT and MR imaging.

Leukemia and Lymphoma

The marrow malignancies lymphoma and leukemia account for 10% to 15% of orbital masses. The two forms of these marrow diseases that most frequently involve the orbit are granulocytic sarcoma (also called chloroma or extramedullary myeloid tumor), which is associated with acute myelogenous leukemia (AML) in younger children, and non-Hodgkin lymphoma (NHL) in older children. In patients with AML, the metastatic focus is referred to as chloroma (derived from the Greek word chloros [green]), because of their green tint. Rarely, this finding is the initial presenting sign of AML, although it more commonly occurs with recurrent disease. A predilection exists for involvement of the subperiosteal space, and on imaging they resemble the bony metastases of a neuroblastoma.

NHL (a tumor composed of B cells) often presents with extranodal disease. Most patients with orbital lymphoma also have systemic disease. The locations involved may include the lacrimal glands, anterior orbit, retrobulbar region, and the superior orbital compartment. CT may demonstrate a hyperattenuating mass with sharply defined margins. MRI findings include hypointense masses on T2-weighted imaging, with associated restricted diffusion on DWI (e-Fig. 7-17, A and B).

Dermoid and Epidermoid Cysts

Dermoid and epidermoid cysts are congenital developmental ectodermal inclusion cysts, and they constitute up to 5% of all orbital masses. Both dermoids and epidermoids arise from entrapped embryonic epithelium, often within the orbital sutures, but they also may be intraorbital or even corneal in location. Epidermoid cysts contain epithelial elements and cholesterol crystals and may be bounded by a thin capsule, whereas dermoid cysts may contain dermal appendages, including hair and sebaceous glands, and are surrounded by a fibrous capsule. Dermoid cysts usually appear as a painless subcutaneous nodule, and they mainly cause cosmetic deformity, but later in life they may grow, partially rupture, and become inflamed and symptomatic. Imaging sometimes is indicated when deep extension of the lesion is suspected and cannot be ruled out clinically.

Dermoid and epidermoid cysts may occur anywhere within the orbit, but most reside in the superolateral aspect of the orbit, at the frontozygomatic suture, or in a superonasal position at the frontolacrimal suture. Osseous remodeling may occur but without associated periosteal reaction. These lesions are well-demarcated, cystic-appearing extraconal masses with differing degrees of fatty content. Uncomplicated superficial dermoid cysts are well depicted on orbital CT without the need for IV contrast because these lesions should not enhance (Fig. 7-18, A). MRI is superior for more detailed depiction of possible intracranial connection and the presence of a potential sinus tract. These lesions are hyperintense on T1-weighted imaging because of their fatty content. Mild rim enhancement occasionally may be seen and is considered normal, whereas the appearance of a more irregular type of enhancement is suggestive of prior rupture with a secondary inflammatory reaction. Epidermoid cysts are hyperintense on fluid attenuated inversion recovery sequences and exhibit restricted diffusion on DWI (Fig. 7-18, B and C).

Langerhans Cell Histiocytosis

LCH is a granulomatous disease resulting from proliferation and infiltration of abnormal histiocytes within various tissues. Orbital lesions occur mainly in young children ages 1 to 4 years. Orbital disease may accompany widespread disease, but occasionally it may be the first manifestation of LCH. The lesions arise from the orbital bone or bone marrow and spread directly to the orbit. Orbital disease may present clinically with proptosis and rapidly enlarging periorbital masses. CT demonstrates expansile soft tissue masses associated with smoothly marginated (“punched out”) areas of osseous destruction in the posterolateral orbits, with a predilection for the frontosphenoid sutures (e-Fig. 7-19, A). MR imaging demonstrates periorbital heterogeneous lesions that may demonstrate blood-fluid levels and restricted diffusion (e-Fig. 7-19, B). The masses exhibit diffuse enhancement on CT and MRI. Evaluation for intracranial extension is imperative on postcontrast sequences (e-Fig 7-19, C). Discovery of a solitary orbital LCH lesion necessitates additional examination for other possible sites of involvement. Multiple soft tissue masses may resemble neuroblastoma metastases by certain imaging features; that is, both lesions may demonstrate restricted diffusion, diffuse enhancement, and intraosseous and extraosseous components. The type of osseous involvement may help to distinguish the “clear-cut” margins of LCH from the permeative pattern and aggressive periosteal reaction of a neuroblastoma. Orbital LCH also can simulate the imaging appearance of an RMS tumor with bone invasion, although bone destruction with LCH typically is more pronounced.

Orbital Pseudotumor (Idiopathic Orbital Inflammation)

An orbital pseudotumor, which is a condition of unknown etiology, represents a noninfectious infiltration of the orbital structures by lymphocytes and plasma cells, usually without associated osseous involvement. The disease may present as unilateral, isolated involvement of the extraocular muscles but also may manifest with a more diffuse pattern that involves multiple orbital sites. It also can present with neuritis or an extrabulbar mass. CT and MRI are equally effective in depicting the extent of disease (Fig. 7-20).

In children, orbital pseudotumor presents with an acute onset of painful proptosis and painful eye movement. The clinical presentation of orbital pseudotumor may be the best discriminator between this disease process and Graves disease (formerly known as Graves ophthalmopathy and now referred to as thyroid-associated orbitopathy). Orbital myositis usually appears as enlargement of the extraocular muscles with mild surrounding inflammatory changes and anterior extension into the tendinous insertion. The imaging features of orbital myositis may be fairly similar to the early stage of thyroid-associated orbitopathy, although the tendinous portion/insertion of the extraocular muscles is spared in patients with thyroid-associated orbitopathy. Excellent response to steroid treatment with cessation of pain is typical for persons with orbital pseudotumor. In rare cases, a biopsy is necessary to exclude malignancy.

Osteoma

Osteomas are benign, slow-growing, bone-forming tumors. Although osteomas of the facial region are not common, they sometimes occur within the region of the paranasal sinuses. If a lesion is of a large enough size and occurs within either the frontal or ethmoid sinus, an adjacent bony break through into the orbit can occur, mimicking an orbital lesion.

Osteomas within the orbits demonstrate typical imaging features of a broad-based expansile osseous mass, sometimes with an inner ground-glass lucent area, surrounded by dense compact bone. Osteomas usually do not cause bony destruction, even when the lesions are large in size. CT is the best imaging modality to delineate the lesion’s characteristics and extension (e-Fig. 7-21). MRI findings may be confusing, because the mature dense bone of the osteoma (and its absence of protons), composing most of the lesion’s volume, may not be distinguishable from the air in the paranasal sinuses.

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