CLINICAL HISTORY

A 43 year male presented to trauma services with loss of consciousness after being trampled by a horse. No focal neurological deficit was observed. Pupils were equal and reactive to light, with intact extra ocular muscle movements. Fundoscopy however showed a subretinal mass in the left eye.

IMAGING FINDINGS

Emergency room head CT without contrast was initially reported as a left globe superior temporal quadrant subretinal hemorrhage with intact scleral margins (figure 1). Intracranial contents were normal. Fundoscopic examination by an ophthalmologist showed a sub retinal mass prompting further investigation.
Orbital MRI with and without contrast shows a para-midline left globe superior temporal quadrant choroid layer lesion slightly T1 hyperintense prior to contrast injection and with homogeneous enhancement after. This favored the diagnosis of choroidal melanoma rather than hemorrhage (figures 2 and 3).
PET CT showed no hypermetabolic lesion or systemic disease (Figure 4).
Biopsy for histopathology however confirmed the presence of melanoma, which was treated with an intraocular radioactive brachytherapy plate.

IMAGES

DISCUSSION

The uvea is a highly vascular pigmented layer between the retina (inner) and sclera (outer), divided into the iris (anterior), ciliary body and choroid (posterior) (Figure 5).
Malignant uveal melanoma (MUM) is the most common primary tumor of the globe in adults (1). MUM is most frequently seen in men around the age of 60. Risk factors include caucasians with fair skin and light iris color. Ultraviolet light has not been associated with MUM, except in certain occupations such as arc welders.
MUM arises from melanocytes within the uvea (2). 
It is classified into anterior uveal if the tumor arises from the iris (3%), and posterior uveal when it originates from the choroid (90%) or ciliary body (7%) (3, 4). For this reason MUM is frequently called "choroidal melanoma". Iris melanomas occur most frequently in the inferior quadrants (45%).
Ophthalmoscopic examination shows the typical appearance of a pigmented dome or mushroom-shaped mass. A, B and Doppler ultrasound modes are the most common diagnostic tests, which may diagnose >95% of cases. Additional tests include fluorescein angiography, optical coherence tomography, autofluorescence and Indocyanine green angiography, when appropriate.
CT identifies most MUM as hyperdense, elevated mushroom shaped choroidal lesions with post-contrast enhancement.
MRI is the modality of choice for MUM mapping, since it is more sensitive and specific than ultrasound in detection of extra-ocular extension (3). The tumor is characteristically hyperintense on T1 weighted images, high signal on FLAIR sequences and hypointense on T2 weighted images compared to the vitreous humor, due to the paramagnetic properties of melanin (short T1 and T2 relaxation times). MUM exhibits different patterns of enhancement which seem to correlate with the degree of malignancy and extraocular extension, being helpful to monitor response to therapy. Buerk et al (5) identified three patterns of enhancement—0% to 20%, 20% to 50%, and >50%. More aggressive lesions showed stronger, rapid enhancement (>50%). 
In the AJCC TNM staging for posterior uveal melanoma, T is classified based on tumor basal width and thickness and subdivided further to reflect ciliary body involvement and extra-scleral extension. 5-year survival is estimated to be 100% for patients with T1 tumors, 90.4% in T2 and 50% in T3, T3a or T4. FNAC /biopsy are definitive when a diagnosis cannot be established by clinical or imaging findings alone. Treatment includes brachytherapy, laser photocoagulation, photodynamic therapy, transpupillary thermotherapy (TTT), local tumor resection or even enucleation in cases of diffuse melanoma /extraocular extension.