Ординатура / Офтальмология / Английские материалы / Imaging of Orbital and Visual Pathway Pathology_Muller-Forell_2005

6.3.2

Tumor-like Lesions

6.3.2.1

Fibrous Dysplasia (Jaffé-Lichtenstein Syndrome)

Fibrous dysplasia is a benign, developmental disorder of the bone, characterized by replacement of normal medullary bone by fibrous connective tissue

with immature bone trabeculae, primarily affecting the spongy bone substance, although in rare cases the cortex of the bone may also be affected (Lichtenstein and Jaffé 1942; Freyschmidt 1993; Jaffe et al. 1997; Wenig et al. 1998). It appears to represent an arrest in the maturation of primitive fibrous stroma in the woven bone stage, thus preventing the normal replacement of immature woven bone by lamellar bone, and is obviously caused by a specific mutation

of the Gs alpha gene (Marie et al. 1997; Wenig et al. 1998). Fibrous dysplasia may occur in a monostotic form in 70%,oligoor polyostotic appearance is seen in 30% of cases,with the latter developing at an earlier age than the former. In rare cases, fibrous dysplasia occurs in combination with endocrine dysfunction and cutaneous hyperpigmentation (precocious puberty, hyperthyroidism), the McCune–Albright syndrome (MAS) (Albright et al. 1937; Freyschmidt 1993; Marie et al. 1997; Wenig et al. 1998). Craniofacial lesions occur in 50% of patients with oligoor polyostotic fibrous dysplasia, and in nearly 100% of patients with a severe polyostotic form (Megerian et al. 1995). The most frequently affected bones of the craniofacial skeleton are the ethmoid,sphenoid,frontal (Fig.6.106),and temporal bones (Mohammadi-Araghi and Haery 1993). Detection of fibrous dysplasia is mostly incidental, but if clinically symptomatic,it correlates with the involved region and the extent of the involvement (Katz and Nerad 1998). The typical age of presentation is late childhood or adolescence, because especially in monostotic forms (Fig. 6.107), the disease is self-limited with stability at the onset of puberty (Henry 1969; Jaffe et al. 1997; Wenig et al. 1998). Histologically, irregularly shaped trabeculae of osteoid and immature bone are seen arising metaplastically from the fibrous stroma, forming odd geometric patterns, resembling Chinese letters (Mohammadi-Araghi and Haery 1993). Surgical treatment is required in cases of progressive facial deformity (Fig.6.106) or cranial,and particularly optic, nerve involvement (Fig. 6.188) (Papay et al. 1995; Katz and Nerad 1998). Radiation therapy is known to link

directly to sarcomatous transformation of the lesions and should be avoided (Stanton and Montgomery 1996; Wenig et al. 1998; Freyschmidt 1993).

As histopathologic differentiation from ossifying fibroma may sometimes be difficult, the presence and consideration of radiological features are crucial for the definite diagnosis. CT has replaced plain film and represents the method of choice in the initial diagnosis and definition of the extent of fibrous dysplasia, especially with 3D-reformation for preoperative planning of esthetic surgery in patients with extensive facial involvement (facies leontina). In craniofacial lesions, three morphologically different types of radiologic features of fibrous dysplasia are known, depending on the stage of development and the degree of fibrous stroma replacement:

–the pagetoid pattern represents the most common form (56%), especially in polyostotic fibrous dysplasia, showing mixed density of the thickened external and internal table.

–involvement of the skull base, with preference of the sphenoid bone, often exhibits a sclerotic pattern (23%) with a diffuse, sometimes uniform homogeneous density of the spongy layer (“ground glass pattern”) in the enlarged segment, and a wide margin to the unaffected bone.

–the cystic type (21%) is characterized by an expansion of the entire bone, with cortical thinning of the external (rarely the internal) tabula, mostly with a sharp sclerotic border to the unaffected bone (Freyschmidt 1993; Wenig et al. 1998) (Fig. 6.106).

Normal segments of cortex between areas of expansion lead to a scalloped pattern,and the absence of sharp margins in focal thinning of bone cortex is characteristic for fibrous dysplasia (Stanton and Montgomery 1996; Jaffe et al. 1997).

MRI patterns of fibrous dysplasia show a nonhomogeneous low signal with a sharp margin on T1weighted images, while on T2-weighted images areas of various signals represent the protein-rich or true cystic areas of fibrous dysplasia. Signal enhancement after contrast administration may be seen, representing the presence of vessels rather than cellular activity (Casselman et al. 1993).

In the differential diagnosis, the fact that the disease normally stabilizes in early adulthood should be emphasized, as the age of the patient at presentation is an important criterion contributing to an accurate assessment. Although homogeneous sclerosing of the sphenoid bone may suggest fibrous dysplasia, most adults older than 35 or 40 years and new asymmetry of the race and orbit as a rule harbor intraosseous meningioma of the sphenoid (Fig. 6.108, Fig. 7.32).

Fig. 6.107. A 15-year-old girl with facial deformation in the absence of visual problems. Diagnosis: fibrous dysplasia (Jaffé–Lichtenstein disease). Coronal CT, showing characteristic sclerosing of the entire maxillary bone, leading to deformation of the right orbital floor

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Fig.6.108a–f. A 50-year-old woman with slowly progressing protrusion of the right eye persisting for the past 3 years, and concomitant nonlocalized headache, but without neurological symptoms. Diagnosis: meningioma of the right sphenoid wing. CT: a Axial HR image in bone window at the level of the optic canal. Compared with the left side, the lateral sphenoid wing, the zygomatic bone, and the rostral part of the temporal bone are characterized by irregular sclerosis of the entire bone, including the tabula interna, external, and diploë with exostotic growth into the temporal fossa. b Coronal HR-CT with irregular, knotty sclerosis and thickening of the right sphenoid, also invading the frontal and zygomatic bone. c Oblique coronal view of a 3D-CT reconstruction. MR: d Axial T1-weighted native view (corresponding to a). Note thickening of the temporopolar dura (small arrows). e After i.v. gadolinium, not only the invaded temporopolar dura shows signal enhancement, but some dotted, hazy signals are also seen in parts of the thickened bone. f Coronal T1-weighted native image (corresponding to b) with superior visualization of the space-occupying effect with compression of the posterior part of the upper orbit, compared to the left side

Orbital Pathology

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6.3.2.2

Ossifying Fibroma

Ossifying fibroma represents the second most common fibro-osseous lesion after fibrous dysplasia. This benign, indolent, fibro-osseous tumor of bone is found in the cranial region and occurs in almost all cases in a monostotic form. Often diagnosed incidentally in an older, predominantly female population, it may also be seen in children, where especially maxillary lesions can be extended, demanding a wide local excision (Marvel et al. 1991). Arising from the mesenchyme of the periodontal ligament, these tumors are composed of highly cellular fibrous stroma and islands of bone (Nemzek et al. 2000). On CT, they present as a large mass of heterogeneous density (Fig. 6.109) and may in some instances have a radiodense rim of different width. On MRI, ossifying fibromas usually show an intermediate signal with moderate contrast enhancement on T1-weighted, and a hypointense signal on T2-weighted images (Wenig et al. 1998).

6.3.2.3 Osteoma

Osteomas are benign, slowly growing tumors with a preference for the craniofacial region, occurring most commonly in the frontal and ethmoidal sinuses (Earwaker 1993). Histologically, osteomas are composed of irregular mature bony lamella and are sometimes rimmed by osteoblasts. Interosseous spaces may be loosely filled with highly vascularized, moderate cellular stroma of fibrous, fibrovascular, or fatty tissue, that may lead to a misinterpretation of a osteosarcoma (Wenig et al. 1998; Lang and Sulzbacher 2001). Osteomas are usually asymptomatic and found incidentally; patients may present with headache, facial deformity, or ocular disturbances. On native X-ray, osteomas are identified as sharply delineated, dense lesions protruding into or developing from a sinus. On CT, the origin of the osteoma is optimally delineated (Fig. 6.110). Additional contrast administration may provide additional information as to whether a secondary pathology, e.g., an additional inflammation (Fig. 6.111), is apparent; on MRI contrast material may define the interosseous tissue (Fig. 6.110).

The differential diagnosis should include not only ossifying fibroma (Fig. 6.109), fibrous dysplasia (Figs. 6.106, 6.107), but also calcified meningioma (Fig. 7.27).

6.3.3

Inflammatory Lesions

6.3.3.1

Orbital Infections

Orbital complications of paranasal sinusitis are relatively common in children but uncommon in adults. On the basis of clinical and imaging criteria, they are classified as bacterial preseptal cellulitis, subperiostal abscess, orbital abscess, and cavernous sinus thrombosis (Chandler et al. 1970; Hershey and Roth 1997; Eustis et al. 1998).

Preseptal cellulitis, a bacterial inflammation of the skin and the subcutaneous tissue, represents the most common orbital complication of inflammatory paranasal processes, clinically presenting as erythema with

severe pain, rarely as lid edema, chemosis, and proptosis, or even limited eye motility. The orbital septum as a reflection of the periorbita at the anterior margins of the orbit provides an effective barrier against intraorbital infection,as does the periorbita at the lamina papyracea (Eustis et al. 1998). This isolated disease normally does not require orbital imaging, but in case of a tentative diagnosis, CT may demonstrate radiographically normal tissue posterior to the orbital septum.

Inflammatory edema, clinically presenting with eyelid swelling and proptosis, is the first manifestation of orbital involvement of paranasal sinusitis, representing postseptal cellulitis, an affection of the proper orbit posterior to the orbital septum. Postcontrast studies demonstrate some enhancement of the extraconal fat adjacent to the involved sinus (Figs. 6.112–6.114). Orbital phlegmon is an advanced

stage of postseptal cellulitis, characterized by softtissue infiltration along the orbital wall with replacement of the peripheral fat and subperiosteal space by soft tissue (Figs. 6.115, 6.116) (Eustis et al. 1998).

The formation of a subperiostal abscess is due to the spread of the infection through the congenital dehiscences and foramina of the thin orbital bones as well as (less common) to thrombophlebitic spread (Eustis et al. 1998). In addition to chemosis, marked eyelid swelling and erythema of the lids, limited eye motility, or even visual loss, caused by a rapid increase of intraorbital pressure, may occur (Harris 1994; Eustis et al. 1998). Although some patients respond to conservative medical treatment, surgery is required in the majority of cases to prevent deterioration and visual loss. Imaging is thus required in emergency situations. On contrast-enhanced CT, a sharply defined, extraconal, space-occupying mass with marginal ring enhancement is seen, sometimes displacing the corresponding rectus muscle. The differentiation from spontaneous subperiosteal hematoma, especially in rare cases of chronic sinusitis (Griffeth et al. 1997), might be difficult (Fig. 6.117). On MRI, the subperiosteal abscess is characterized by an intermediate signal on T1-weighted and proton density images that appears hyperintense on T2-weighted images with rim enhancement of the capsule after contrast administration. Intracranial complications as, e.g., epidural or subdural abscesses, purulent meningitis, or cavernous sinus thrombosis, are major complications with a mortality rate of about 21% (Maniglia et al. 1989).

Because of modern antibiotic therapy the development of true orbital abscess secondary to paranasal sinusitis or dental infection is rather uncommon (Eustis et al. 1998).

Cavernous sinus thrombosis results from different causes, i.e., the spread of infection to sinonasal cavities, to the middle third face, or a paraneoplastic disorder (Fig. 6.59) (Dolan and Chowdhury 1995; Berenholz et al. 1998; Eustis et al. 1998). On CT and MRI, these severely ill patients with signs of meningitis and multiple, bilateral cranial nerve palsies present with filling defects in the engorged cavernous sinus combined with enlargement of the superior ophthalmic vein and extraocular muscles (Schuknecht et al. 1998). On MRI, the thrombosis of the superior ophthalmic vein presents as a hyperintense area within the lumen of the vein (Eustis et al. 1998).

Fungal orbital inflammations, caused with great frequency by mucormycosis and Aspergillus, are less common than bacterial infections. They are often found in patients with a history of uncontrolled diabetes mellitus, as well as in immunocompromised patients. The role of imaging is its clear demonstration of the relationship between the nasal sinus, orbit, and cranial disease (Eustis et al. 1998). On CT, a nonspecific thickening of the sinus mucosa, at times combined with bony erosion,is seen in mucormycosis infection, which is not always different in appearance from Aspergillus sinusitis. A nonspecific, but characteristic finding on T2-weighted MRI is the hypointensity of mycotic infection, and some calcification of the intrasinusoidal mass on CT (Eustis et al. 1998).

Fig. 6.112. A 9-month-old girl with swollen left lid and febrile state. Diagnosis: lid abscess. Axial contrast-enhanced CT with protrusion of the left globe, inflammatory infiltration of the left lid with necrosis rostral to the zygomatic process, and slight extraconal postseptal infiltration between the lateral orbit wall and the lateral rectus muscle (arrow)

Fig. 6.114. A 60-year-old woman with painful, reddish swelling and proptosis of the left eye after neurosurgical operation for meningioma. Diagnosis: orbital phlegmon. Axial contrastenhanced CT with irregular, contrast-enhancing, space-occupy- ing lesion, showing both preand postseptal expansion as well as infiltration of the orbital fat and the medial rectus muscle. (With permission of Müller-Forell and Lieb 1995b)

Fig. 6.113a,b. A 40-year-old man with reddish, swollen left lid and decreased motility of the left globe; state after an accident with orbital floor fracture 5 years previously. Diagnosis: ethmoid pyocele,cause of orbital phlegmon.CT: a Axial contrast-enhanced view with dilated,infected,medial ethmoid cell and preseptal subcutaneous infection of the medial orbital region. Note the presence of dehiscence from the left zygomatic bone and from the zygomatic process of the left temporal bone,representing a sequel of the accident. b Coronal view in bone window where the metallic artifacts after surgical therapy of the orbital floor fracture and the secondary low level of the left orbital floor are visualized

Fig. 6.115a,b. A 13-year-old girl with acute purulent pansinusitis and acute exophthalmos of the right eye. Diagnosis: subperiosteal abscess. CT: a Axial contrast-enhanced image with bilateral purulent ethmoidal cell infiltration and extraconal, preand postseptal abscess of the right orbit. b Coronal con- trast-enhanced view, demonstrating an additional, sharply demarcated, subperiosteal formation, causing dislocation of the muscle cone