Ocular melanoma

Precontrast hyperdensity related to melanin.

Postcontrast hyperdensity related to moderate enhancement + melanin.

Many lesions are found incidentally when CT is performed for other reasons.

CT should not be used as the preferred imaging method when MRI can be performed.

Minimizing radiation dosages should be kept in mind when imaging orbits because radiation is clearly cataractogenic.

In today’s radiation-conscious climate, no radiation (such as in MRI) tops any CT radiation dose, at any time.

3D reconstructions are often useful.

CT is more sensitive to extrascleral extensions, but will not detect small extensions, particularly those involving emissary veins.

T1 bright.

T2 dark.

T1 + Gd = moderate enhancement.

Problem: Effusions.

• Well visualized.

• Slightly bright on T1 (protein and blood).

• Bright on T2.

• Do not enhance.

Preferred imaging method owing to its lack of radiation and multiplanar capability.

Probably the modality of choice for imaging the orbit and initial work-up of this type of lesion.

Clearly a superb tool for staging.

Ultrasound (US) is clearly more cost effective and may suffice for some follow-up imaging.

MRI is superior to US in cases where the tumor is large and extends posteriorly (see Figure 18-3 ).

Most intraocular melanomas are detected clinically or by using US.

Most ocular choroidal melanomas can be evaluated by US.

US is a useful adjunct to fundoscopic examination if the vitreous chamber is difficult to examine because of:

• Cataract.

• Vitreous hemorrhage.

Good for monitoring size during radiation treatment.

Good for evaluating tumors inside the globe.

It is relatively insensitive to extrascleral extension.

Low to medium internal reflectivity, homogeneous internal structures, and internal vascularity.