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

(Figs.6.25,6.35),or retro-ocular hematoma (Figs. 6.37). In extensive facial injuries, where imaging is primarily performed to exclude extraconal and/or intracerebral lesions, damage to the globe may also be seen. In case of a suicidal patient with bullet injury in the absence of direct global trauma (Fig. 6.198), rupture of the globe may be caused by the development of shock waves. Subretinal/subchoroidal hemorrhages were found in a young man after an explosion in the course of a black powder experiment (Fig. 6.28). In cases with foreign body injuries, CT can define the exact location of the object in the respective orbital structure (Fig. 6.36). In the case of a young man who was admitted to hospital with an acute, complete visual deficit as a result of an injury suffered doing home repair work, ophthalmoscopy could not identify the location of a metal fragment, which had obviously perforated the globe twice, while CT accurately defined the fragment location at the site of the papilla (Fig. 6.31).

Hemorrhagic choroidal detachment may occur as a complication of intraocular surgery. Although the diagnosis can be made with ultrasound, MRI (especially using a surface coil) is the method of choice in defining the extent and location of the hemorrhage, which is of particular importance with a view to the prognosis for the involved eye (Mafee and Peyman 1984) (Figs. 6.26, 6.27).

Phthisis bulbi referring to a scarred, retracted, shrunken globe may be defined as a type of secondary (developmental) microphthalmos (Harnsberger 1990) (Fig. 6.38). It is generally associated with dystrophic calcification and may be the result of infection, penetrating trauma (Fig. 6.39), repeated orbital surgery, or noninfectious inflammation (Carmody 2000).

Fig. 6.38. A 66-year-old woman with phthisis bulbi of the right globe. Axial CT: small globe with calcification of the lens and a part of the globe

6.2

Conal/Intraconal Area

6.2.1

Solid Tumors

6.2.1.1

Peripheral Nerve Tumors

The orbit is host to a great number of nerves, including the motor branches of cranial nerves III, IV, VI, sensory branches of cranial nerve V, as well as sympathetic and parasympathetic branches,each of which is a potential starting-point for tumor growth. Peripheral nerve tumors account for about 4% of all orbital neoplasms with a preference for (plexiform) neurofibromas and schwannomas (Henderson 1994). Although their location is discussed in special chapters on these tumors, they may also be located in the intraconal as well as extraconal orbital compartment, depending on their origin in the course of the multiple nerves and their branches.

6.2.1.1.1 Schwannoma

Schwannomas(synonyms:neurinoma,neurilemoma) are benign, slowly progressing, encapsulated tumors (WHO I) composed of differentiated spindle-shaped neoplastic Schwann cells, mostly including solid cells (Antoni A pattern) and loosely textured, often lipidic areas (Antoni B pattern). Although not exclusively, they do have a high incidence in patients with neu-

rofibromatosis type II (NF 2). Orbital schwannomas account for only 1%–8% of all orbital tumors (Housepian et al.1982; Henderson 1994).They usually originate from sensory branches of the trigeminal nerve (Jakobiec and Font 1986) and present as globoid, encapsulated masses measuring from a few millimeters to centimeters in size (Woodruff et al. 2000). Patients with orbital schwannoma are normally adults and present with a slowly progressing,mostly painless proptosis (Fig. 6.40) (De Potter et al. 1995).

Imaging shows a well-defined, intraor extraconal, ovoid to elongated mass (Fig. 6.40), suggestive of an expanding peripheral nerve tumor. On MRI, schwannoma may present with a homogeneous or just as well heterogeneous signal, depending on the histologic features of the tumor. On T1-weighted images, they have an isoto hypointense signal in relation to the orbital fat and demonstrate a varying degree of contrast enhancement (Figs. 6.41, 6.93), with a more intense signal enhancement of the myxoid portions of the tumor (Antoni B) (De Potter et al. 1995; Abe et al. 2000). On T2-weighted images, these tumor portions show greater signal intensity compared with the more cellular parts, which renders the differential diagnosis from cavernous hemangioma, eccentric optic nerve sheath meningioma (Fig. 6.178), neurofibroma (Fig. 6.94), melanoma (Fig. 6.45), fibrous histiocytoma,and hemangiopericytoma (Fig.6.92) more difficult (De Potter et al. 1995).

As another differential diagnosis,lymphoid hyperplasia, extending along peripheral sensory nerves (Fig. 6.167) or fascial planes and muscles, represents an extremely rare entity (Yeo et al. 1982).

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6.2.1.1.2 Neurofibroma

Neurofibromas (WHO I) consist of neoplastic Schwann cells, perineurial-like cells, and fibroblasts in a matrix of collagen fibers and mucosubstances (Woodruff et al. 2000). Plexiform neurofibromas, the most common type affecting the orbit, present as elongated, multinodular, nonencapsulated lesions as they involve multiple trunks or fascicles of a large nerve, sometimes suggesting the image of a “bag of worms” (Woodruff 1996). These highly vascular, poorly defined, and diffusely infiltrating tumors represent an overgrowth of the components of a peripheral nerve (Harkin and Reed 1969). Diffuse neurofibroma, seen in the first decade of life, represents the most frequent manifestation of neurofibromatosis of the orbit, while localized neurofibromas are

W. Müller-Forell and S. Pitz

seen in middle-aged patients (Bilaniuk et al. 1990; De Potter et al. 1995; Carroll et al. 1999).

Neurofibromatosis type 1 (NF1) can be found in patients with multiple neurofibroma, although this tumor may occur as a sporadic, solitary nodule unrelated to any syndrome (Woodruff et al.2000).Localized, singular neurofibromas present as a slow-grow- ing, painless, well-circumscribed mass leading to axial exophthalmos.

Imaging in isolated neurofibroma depicts a circumscribed, oval to elongated, encapsulated, intraor extraconal mass with mild contrast enhancement on CT (Fig. 6.42). MRI shows a serpiginous, irregular, often infiltrating mass, which may at times infiltrate the orbital fat with marked contrast enhancement, caused by the high vascular component (Bilaniuk et al. 1990; Carroll et al. 1999). On T1-weighted images, neurofibromas are seen as homogeneous iso-

Orbital Pathology

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Fig. 6.42a–e. A 43-year-old man with known NF 1 and slowly progressing exophthalmos of the right side. Diagnosis: recurrent multiple intraorbital neurofibroma. CT: a Axial view of the inferior part of the orbit with a lesion lateral to and displacing the inferior rectus muscle. b Coronal view showing the tumor between the inferior and lateral rectus muscle. An additional tumor which is sharply differentiated from the surrounding tissue is visualized between the superior rectus and the oblique muscle (arrow), the latter with inferior displacement to the level of the medial rectus muscle. A comparison with the contralateral orbit demonstrates enlargement of all muscles. MRI: c corresponding coronal native T1-weighted image. d Following contrast enhancement, the smaller superior tumor exhibits an increase in signal intensity, compared with the inferior tumor as well as with the rectus muscles. (MR images with permission of Röntgeninstitut Unna.) e Histology (¥55): dense network of a fibrillary connective tissue in the endoneural space of an enlarged peripheral nerve, surrounded by a thickened perineurium (with permission of Dr. Bohl, Department of Neuropathology, Medical School, University of Mainz)

to hypointense tumors, while on T2-weighted images, they present with a homogeneous to heterogeneous signal characteristic (Fig. 6.94) (De Potter et al. 1995), sometimes with expansion into the bony walls and/or enlargement of the orbit (Bilaniuk et al. 1990; De Potter et al. 1995). Plexiform neurofibromas present as a poorly defined, irregular mass.

6.2.1.2 Lymphoma

The term lymphoma (syn. lymphoproliferative disorder) describes a heterogeneous group of neoplasms of the lymphoid system with distinct entities defined by clinical, histological, immunological, molecular, and genetic characteristics (Asao et al. 1998; Valvassori et al. 1999). With an increasing incidence, orbital lymphomas account for up to 55% of all malignant orbital tumors (Margo and Mulla 1998), whereas low-grade non-Hodgkin lymphomas (NHL) account for about 10% of all orbital masses (Shields et al. 1984b). Although most lymphoid tumors arise from lymph nodes, orbital lymphoma may represent the only or first manifestation of a generalized lymphoma (Fig. 6.43) or be associated with a generalized systemic disease (Valvassori et al.1999). Lymphoproliferative disorders include benign, atypical, and malignant lesions. Most of those involving the orbit are B-cell lymphomas (White et al. 1996), although orbital lymphomas primarily belong to low-

grade non-Hodgkin variants or extranodal mucosaassociated lymphoid tissue (MALT lymphoma) (De Potter et al. 1995; Polito et al. 1996; Galieni et al. 1997; Valvassori et al. 1999). The classification of leukemias and lymphomas has undergone radical changes as traditional morphologic and cytochemical descriptive classifications were superseded and replaced by molecular biologic, cytogenic, and immunophenotyping molecular genetic analysis. This analysis enables us to distinguish clonal from polyclonal lymphoproliferations, to determine the B- or T-cell identity of malignancies, the genetic lineage of neoplasms lacking surface antigens, and the developmental stage of early B- or T-cell precursors (Kawamoto and Miyanaga 1997; Specht and

Laver 2000). MALT lymphomas are composed of cells ranging from small lymphocytes with few atypia to small lymphocytes with slightly irregular nuclei, to monocytoid B-cells,all of which have the potential for invasion of epithelial structures (Specht and Laver 2000). Prognosis and management decisions, regardless of whether this involves radiotherapy alone (with excellent local control in MALT lymphoma), systemic chemotherapy alone or in combination with radiotherapy, are determined by anatomic site, stage, and histological features (Bairey et al. 1994; Polito et al. 1996; Valvassori et al. 1999; Agulnik et al. 2001). Orbital involvement in leukemia, a disease of the bone marrow predominantly occurring in childhood, is not common (Valvassori et al. 1999).

Clinical findings in orbital lymphoma include painless, mostly unilateral (in rare cases bilateral; Fig. 6.138) proptosis and motility disturbances in patients (most commonly) older than 50 years. Although any other orbital tissue may be involved (Fig. 6.44), the preferred orbital structure is the lacrimal gland (see Sect. 6.3.4.2.3). The patient presents with extra-axial proptosis, combined with an inferior displacement of the globe and a smooth, palpable mass of pink color in the superior lateral orbit. Even in cases of the rare

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Fig. 6.44a,b. An 82-year-old woman with slowly progressing, painless, unilateral, extra-axial proptosis of the left eye. Diagnosis: lymphoma. Contrast-enhanced CT: a Axial and b Coronal view with a clearly defined retroand suprabulbar located formation with slight enhancement, not separated from the superior rectus muscle, but adapting to the contour of the globe; the latter finding excludes the presence of hemangioma as a specific differential diagnostic criterion. (With permission of Müller-Forell and Lieb 1995)

involvement of extraocular muscles (Fig. 6.43), eye motility is not significantly impaired because of the presence of only a small amount of collagen deposition (Weber et al. 1996b).

6.2.1.3 Miscellaneous

Most malignant tumors of the orbit are metastases from peripheral malignancies, but at times they originate in the orbit itself. Primary melanoma of the orbit (Fig. 6.45), although a rare entity, should be included in the differential diagnosis when a solid, irregular mass is seen which exhibits indifferent, but mainly homogeneous signal characteristics and signs of bony destruction.

6.2.2

Vascular Lesions

The question of whether vascular lesions of the orbit, an important and substantial component of orbital abnormalities, should be classified as vascular tumors or vascular malformations is still being controversially discussed (Mullikan and Young 1988; Bilaniuk

1999). Some authors have proposed classifying these lesions according to their hemodynamic properties as arterial, highor low-flow lesions, or as distensible, nondistensible, or stagnant venous lesions (Rootman et al. 1986). Comparable to the multidisciplinary approach in the management of these lesions, many specialists are involved in the classification process. In view of that fact that there is continuing disagreement as to the most appropriate terminology, we suggest that the compromise solution of combining traditional, familiar nomenclature with pathophysiological terms may be ideally suited to end the current discord and to establish an uniform terminology (Rootman et al. 1992; Bilaniuk 1999). CT and MRI play a crucial role in the management of vascular lesions; they exert a major influence on the choice of therapy, and imaging assists in the definition of the approach if surgery is to be performed (Bilaniuk 1999).

6.2.2.1

Capillary Hemangioma in Childhood

Capillary hemangioma is the most common orbital vascular tumor in childhood. It consists of plump, rapidly dividing endothelial cells with lumina of varying size, pericytes, and multilaminated basement membranes (Mulliken and Glowacki 1982;

Lasjaunias 1997). They may be present at birth or during the first year of life and are more common in girls (Mulliken and Glowacki 1982) (Figs. 6.46, 6.47). They represent an abnormal growth of capillary blood vessels dominated by varying degrees of endothelial proliferation and phases of involution (Teske et al. 1994; De Potter et al. 1995). In the presence of orbital involvement, there is a high risk of visual acuity deficits as well as distortion of extraocular muscles, the cornea, and optic nerve (Deans et al. 1992). Although capillary hemangiomas prefer the superomedial extraconal quadrant of the orbit, expansion may be seen in any orbital compartment (Fig. 6.47). For still unknown reasons (Mullikan and Young 1988),capillary hemangiomas frequently show a tendency towards spontaneous involution in childhood (5–10 years of life), sometimes with complete disappearance (Lasjaunias 1997; Bilaniuk 1999).

On imaging, capillary hemangioma presents as a lobulated, irregularly marginated, septated parenchymal mass, slightly hypodense on CT (Figs. 6.46, 6.47) and isoto hyperintense on T1-weighted and moderatelyhyperintenseonT2-weightedMRimages. As in other intraorbital masses, fat-suppressed, T2-weighted or contrast-enhanced, T1-weighted images provide excellent details and facilitate the differential diagnosis from rhabdomyosarcoma or metastatic neuroblastoma, especially if feeding and draining vessels are seen (Bilaniuk et al. 1990;

Bilaniuk and Rapoport 1994; De Potter et al. 1995; Lasjaunias 1997). Some arterial supply may be visible on 2D TOF MR-angiography (De Potter et al. 1995).

Therapy depends on the orbital extent and effect on the visual apparatus and includes laser, cryoor radiation therapy, surgery, or conservative treatment