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

cases per million per year at a mean age of 53 years (De Potter et al. 1995; McLean 1996). Malignant melanomas occur predominantly in Caucasians (ratio 15:1 Caucasians and blacks) (Yanoff and Fine 1975; Margo and McLean 1984). The current WHO classification of tumors of the choroid – in contrast to the former Callender classification – only discerns three histological types, i.e. mixed, epithelioid, and necrotic melanomas (Callender 1931; McLean et al. 1978; Campbell and Sobin 1998). The mixed type consists of spindle B and epithelioid cells. Spindle cell A tumors are currently classified as benign choroidal nevi. Spindle cell tumors have a relatively good prognosis in comparison with mixed or purely epi-

thelioid melanomas (McLean 1995; Mafee 1998). Tumor growth is generally nodular, while flat lesions diffusely infiltrating the uvea are rare. A nodular melanoma may exhibit a well-circumscribed, ovoid or dome-shaped appearance. Bruch’s membrane may rupture with tumor progression, assuming a characteristic mushroom shape (Fig. 6.10) (De Potter et al. 1995; Mafee 1996). The factors associated with a poor systemic prognosis include: (1) older patients (>60 years), (2) large tumor basal diameter and thickness (>15 mm/3 mm), (3) location of the tumor in the anterior uvea and ciliary body, (4) presence of epithelioid cells, and (5) extraocular extension (Char 1978; De Potter et al. 1995; Damato et al. 1996a,b).

The sites of metastasis are liver, lung, bone, kidney, and brain. The question of the most effective therapy is still being controversially discussed, with options ranging from photocoagulation, transpupillary thermotherapy (TTT) to radiation therapy with ruthenium or strontium plaques, local excision, or enucleation (Char 1978; Duffin et al. 1981; Peyman et al. 1984; Osterhuis et al. 1995; Damato et al. 1996a,b; Shields et al. 1998).

Diagnosis of uveal melanoma is usually made by ophthalmoscopy, fluorescein angiography, and ultrasound, with the last-mentioned being indicated especially in lesions smaller than 3 mm (Mafee et al.1985), although imaging with CT or MRI is required when opaque media preclude direct ophthalmoscopic visualization (Shields and Zimmerman 1973; Zimmerman 1973; Harnsberger 1990; Mafee et al. 1985; De Potter et al. 1995; Mafee 1998).

Although most uveal melanomas are seen on CT as elevated, primarily hyperdense, sharply circumscribed, enhancing tumors, high-resolution MRI has become the imaging technique of choice in the definition of retrobulbar/extraocular tumor extension. Melanin produces stable free radicals which cause a paramagnetic proton relaxation enhancement that shortens both T1 and T2 relaxation times, resulting in a moderately high signal on T1-weighted and proton density-weighted scans and signal reduction with moderately low signal on T2-weighted images (Fig. 6.13). This somewhat unique signal pattern is caused by the binding capacity of natural melanin for paramagnetic metal ions (i.e., iron, copper) (Enochs et al. 1997). Hence the well-defined solid tumors pres-

ent (in up to 95%) as hyperintense (with respect to the vitreous body) on T1-weighted sequences and hypointense on T2-weighted images (Damadien et al. 1973; Gomori et al. 1986; Haik et al. 1987; Mafee and Peyman 1987) (Figs. 6.11–6.15). Associated retinal detachment as an area of moderate to very high signal intensity on T1-weighted, PD, and T2-weighted images is better visualized with MRI than CT (Mafee 1996). It is important to know that in some cases an isointense signal is seen on T2-weighted images and that the content of melanin is not always in correlation to the brightness of the signal. Gadolinium-enhanced, T1-weighted images are superior to noncontrast T1weighted images in detecting and delineating malignant melanomas.The additional use of fat-suppressed sequences improves the contrast difference in signal intensity of choroidal melanomas associated with retinal detachment as well as the detection of small melanomas (De Potter et al. 1994, 1996; Flanders et al. 1996). While in most cases the tumor shape is of no specific diagnostic value, the detection of a mushroom or collar-button shaped tumor caused by the growth and rupture through Bruch’s membrane on ophthalmoscopic,US,and CT/MRI (Fig.6.10) is highly suggestive of choroidal melanoma (Mafee 1998).

In addition to retinoblastoma,the differential diagnosis includes choroidal hemangioma (Fig. 6.16) (see Sect. 6.1.2.3.1), choroidal nevi, choroidal detachment (see Sect. 6.1.2.3.5), choroidal cysts, neurofibroma and schwannoma of the uvea, uveal leiomyoma, ciliary body adenoma, as well as retinal detachment, disciform degeneration of the macula, and metastatic tumors (Fig. 6.19) (see Sect. 6.1.2.3.4) (Mafee 1998).

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Orbital Pathology

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Fig. 6.13a–c. A 61-year-old woman with visual deficit. Diagnosis: ciliary body melanoma. Axial MRI: a T1-weighted native image showing the hyperintense tumor in the ciliary body; b Corresponding proton density image with the tumor appearing as hyperintense with signal changing to hypointensity on the T2-weighted sequence (c)

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Orbital Pathology

6.1.2.3.

Miscellaneous Choroidal Lesions (i.e. Choroidal Hemangioma, Choroidal Osteoma, Ocular Hamartoma, Uveal Metastasis, Choroidal Detachment)

Although less than 1% (2 of 413) of enucleated eyes were found to contain choroidal lesions other than malignant melanoma (Collaborative Ocular Melanoma Study, COMS 1998), the differential diagnosis should not fail to also consider other choroidal lesions, as the respective therapeutic regimens differ substantially.

6.1.2.3.1

Choroidal Hemangioma

Choroidal hemangiomas are congenital vascular hamartomas seen in middle-aged to elderly patients with neurocutaneous syndromes. They may present as circumscribed, solitary or diffuse lesions, while histologically three descriptive categories are classi-

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fied (Mafee 1998): cavernous, capillary, and mixed type lesions.

Uveal hemangiomas occur as circumscribed or diffuse, capillary or cavernous angiomatosis, the latter frequently in association with ipsilateral facial nevus flammeus in Sturge-Weber syndrome (Barkovich 2000; Stroszczynski et al. 1998; Mafee 1998; Yan et al. 1998). While the localized form presents on ophthalmoscopy as a well-defined, reddish-orange lesion of the posterior pole of the globe, diffuse uveal hemangiomas may not be readily discernible.

On CT/MRI, choroidal hemangiomas present as lenticular hyperdense/hyperintense (in both T1and T2-weighted images) structures in the juxtapapillary or macular region, and on comparison with the vitreous body (Fig. 6.16), they demonstrate marked/ intense contrast enhancement (Medlock et al. 1991; De Potter et al. 1995; Mafee 1998).

Retinal hemangioma may occur isolated or in Hip- pel-Lindau syndrome (Fig. 6.17). This rare, autosomal dominant, familial multisystem disorder, one of the

neurocutaneous syndromes (syn. phakomatosis), is characterized by multiple hemangioblastomas of the central nervous system with a preference for the cerebellum and spinal cord, angiomatosis of the retina, pancreatic and renal cysts, and a relatively high incidence of renal cell carcinoma (Rubinstein 1972; Sartor 1992; Osborn 1994) (see NF 1,Sturge-Weber). A bilateral or multifocal presentation is characteristic for capillary hemangioma in Hippel-Lindau disease, while a differentiation from the isolated form is not possible by clinical or histological presentation of the retinal angiomatosis. It appears as a reddish nodule with a dilated, tortuous feeding artery and vein in the mid-periphery of the retina (De Potter et al. 1996).

On MRI, sufficiently large retinal hemangiomas (Fig. 6.17) may simulate retinoblastomas or melanomas (depending on the age of the patient). As the diagnosis is based on the typical ophthalmoscopic appearance, the major role of imaging consists of ruling out a possible association with cerebellar and/or spinal hemangioblastomas (Sartor 1992; Osborn 1994; De Potter et al. 1996).

6.1.2.3.2

Choroidal Osteoma

The rare choroidal osteoma (Fig. 6.18) is typically seen in young women before completion of the third

decade of life. This benign ossifying tumor contains marrow, mast cells, loose fibrovascular elements, and mesenchymal cells. The diagnosis can be made clinically and in combination with characteristic ultrasound findings as the choroidal osteoma presents as a yellow-white or orange-red mass in the macula or juxtapapillary region (Mafee 1998), although it is seen as a sharply demarcated, lentiform calcification on CT. On MRI, it presents with a high signal on nonenhanced T1-weighted and low signal on T2weighted images, with marked signal enhancement after gadolinium injection, simulating both retinoblastoma and choroidal melanoma. The enhancement corresponds to the central core of the osteoma, consisting of fatty marrow within the intertrabecular spaces (De Potter et al. 1995; Müller-Forell and

Lieb 1995a; Mafee 1998; Yan et al. 1998).

6.1.2.3.3

Ocular Hamartoma

Ocular hamartomas (syn. retinal astrocytoma) are rare tumors seen most frequently in patients with tuberous sclerosis (Fig. 6.7) or neurofibromatosis, in whom radiological findings may look similar to early retinoblastoma or present with intraocular calcification (Abramson 1982; Margo et al. 1983; Dotan et al. 1991; Mafee and Peyman 1987).

Orbital Pathology

6.1.2.3.4

Uveal Metastasis

The choroid is the most common site of carcinoma metastasis to the eye, as hematogenous embolic dissemination of malignant cells gain access to the eye with the bloodstream via the short posterior ciliary arteries (Michaelson and Campbell 1940; De Potter et al. 1995; Mafee 1996, 1998; Shields et al. 1997). The most common sources of secondary carcinoma are the breast

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and lung (Stoffelns and Dick 2000). In contrast to uveal melanoma, uveal metastasis may occur bilaterally or be multifocal and affects both eyes in about one-third of cases (Mafee 1990). Decreased vision, field deficits, and pain (the latter depending on the intraocular location) combined with rapid progressive tumor enlargement enable the clinical differential diagnosis of choroidal metastasis of distant carcinoma, while the imaging presentation may lead to confusion of uveal metastasis with uveal melanoma (Fig. 6.19).

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Fig. 6.19a–e. A 64-year-old man with suspected choroidal melanoma and a sudden onset of severe pain in the left eye, requiring emergency enucleation. Diagnosis: uveal metastasis from lung cancer. MRI: a Macroscopic view of the left eye demonstrating a 10 mm prominent, barely vascularized, whitish mass in the temporal iridocorneal angle. b Axial T1-weighted view showing a lesion apparently originating in the anterior lateral choroid, pressing against and dislocating the lens. c Corresponding contrast-enhanced image which did not enable exclusion of invasion of the anterior chamber (surgically proven). d Corresponding T2-weighted image demonstrating widening of the anterior chamber and hypointensity of the lesion. e Coronal T1-weighted, contrast-enhanced view showing irregular growth of the tumor