Histopathologically, the vast majority of malignant melanomas of the iris are composed of spindle cells.  These tumors are more benign than malanomas of the ciliary body or choroid and only rarely metastasize.  Malignant melanomas most commonly arise from the posterior uveal structures, the choroid and ciliary body.  The presenting symptoms depend on the location of the lesion.  If the lesion is located posteriorly, the patient will note blurred vision.  Often, the mass is found on routine ocular examination.  Histologically, in the absence of extraocular extension, the major determinants of prognosis are cell type, tumor size, and location.  Cell type is generally categorized under the Callender classification system. 

  Spindle-A cells(#22153,#22169) have slender nuclei with delicate chromatin, ill-defined or absent nucleoli, and no mitotic activity.  Often a longitudinal fold of the nuclear membrane accounts for a prominent streak of chromatin. 

  Spindle-B(#22162,#22171) cells have more plump nuclei containing small but prominent nucleoli and coarse chromatin.  Mitotic figures are common.  Epithelioid cells(#22172) are variable in size but are usually larger and pleomorphic or polygonal.  They exhibit variations in size and shape of their nuclei and may be multinucleated.  Chromatin shows coarse clumping.  Mitotic figures are abundant.  Cells show loss of intercellular cohesiveness.  Lesions composed of exclusively spindle-A cells are now regarded to behave almost like nevi.  The designation of "mixed" cell type implies the presence of a mixture of spindle and epithelioid melanoma cells(#22174).  Spindle-B tumors may also form a fascicular pattern with palisading of the cells. 

  A final classification is that of a necrotic tumor in which necrosis precludes identification of a cell type.  Other histologic findings may include rupture of Bruch's membrane with a mushroom-like out-pouching of the tumor underneath the retina(#22166).  In addition, there may be an associated exudative retinal detachment and also a cystic degeneration of the retina overlying the tumor.  These tumors may extend from the eye by invasion of scleral emissarial channels or vortex veins (#22177,#22175).  Direct invasion of the sclera or optic nerve is much less common.  The tumor may extend into the orbit and may matastasize distantly.  The most common site of the metastasis is the liver(#22178).

See below for other views of malignant melanoma:

-(#22562 [mushroom shaped], #22647, #22650, #22674, #22686, #22689, #22710)

-Choroid (#22541 [fascicular arrangment],           #22583 [mixed type]).

-Iris (#22544, #22644, #22656, #22659,  #22668 [iris and ciliary body with extrascleral  extension]).

-Invasion of Optic Nerve Head (#22613, #22616, #22619, #22625).

-Extraocular extension (#22638, #22662 [through vortex vein], #22695 [through vortex vein], #22698 [posterior extension], #22701 [exra-bulbar extension], #22704 [liver metastasis])

-Epithelioid type (#22553, #22568, #22580, #22716)

-Spindle A type  (#22565, #22665)

-Spindle B type (#22573, #22577,  #22586, #22589)