Primary uveal malignant melanoma

Malignant uveal melanomas, also referred to as choroidal melanomas, are the most common primary tumour of the adult eye ³. 

Epidemiology

Malignant melanoma of the uvea is the most common primary intraocular malignancy and is predominantly seen in Caucasiansthe White population ⁵. The incidence of these tumours increases with age, with only 2% of tumours found in patients younger than 20 years of age ⁶. 

Clinical presentation

Clinical presentation depends on the location. When the tumour is located on the iris, then it may be apparent to the patient or friends and family as a brown nodule. Choroidal or ciliary body tumours are only identified incidentally on fundoscopy or as a result of retinal detachment or advanced disease.

Pathology

Uveal melanomas arise from the ciliary body or the choroid. Three histological types are recognised ⁵: 

• mixed melanoma: containing both spindle B cell and epithelioid cells
• epithelioid melanoma
• necrotic melanoma

Radiographic features

Ultrasound

Ultrasound is an excellent modality for examining the globe and can visualise small plaque-like or discoid uveal melanoma, with a thickness of less than 3 mm, which are usually difficult to assess on CT or MRI. Features include ⁴: 

• solid low to medium echotexture
• internal vascularity
• collar button shape
  • this is the classic shape but not always the case
  • represents tumour having broken through Bruch's membrane
  • tumours may be irregular, lobulated or domed

Other features sometimes present include retinal detachment, posterior scleral bowing, choroidal excavation and vitreous or subretinal seeding. Additionally, larger tumours are often significantly sound attenuating ⁴.

CT

CT is able to identify most uveal melanomas which appear as elevated, hyperdense sharply marginated lenticular or mushroom-shaped lesions, which enhance with the administration of contrast.

MRI

MRI is the modality of choice for assessment of malignant uveal melanomas ^5-6,6:

• T1/orPD
  • uveal melanomas are seen as moderately high signal mass lesionlesions (melanin and haemorrhage are responsible for the high signal)
  • associated exudative retinal detachment is moderately high signal
• T2
  • moderately low signal mass lesion
  • associated exudative retinal detachment is moderately high signal
  • haemorrhagic subretinal fluid has a variable signal pattern
• T1 C+ (Gd)
  • tumours enhance
  • fat suppression useful in detecting extraocular extension

Treatment and prognosis

Treatment for uveal malignant melanoma depends on tumour size and clinician's preference. Options include photocoagulation, transpupillary thermotherapy (TTT), brachytherapy, hadrontherapy ^11-12,12, local excision, or enucleation ^5-6,6.

Poor prognostic factors for systemic disease include ⁵:

• older age: >60 years of age
• larger tumours
• anterior location within the globe
• epithelioid cells (i.e. mixed or epithelioid histology)
• extraocular extension, which usually occurs along the ciliary vessels and nerves, and less commonly along the optic nerve ⁹

Systemic metastases may be widespread (liver(liver > lung > bone > kidney > brain> breast) ⁶. They can metastasizemetastasise late to the liver, with delays of 10 to 15 year from the presentation. 

Overall survival depends on tumour size, extraocular spread, and metastases. Even small (<10 mm diameter, <3 mm thickness) tumours still carry a 10-15% 5-year mortality ⁶.

Differential diagnosis

• retinoblastoma
• uveal metastases
• choroidal detachment
• choroidal haemangioma
• choroidal cyst
• uveal neurofibroma
• uveal schwannoma

See also

• ocular pathology
• orbital pathology (an approach)