Metastatic Melanoma

Published on 19/07/2015 by admin

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Last modified 19/07/2015

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 Most common sites of metastases: Skin, lymph nodes (75%), lung (70%), liver (58%), CNS (54%), GI tract (40%)

image Most common sites in abdomen: Liver and small bowel
• Melanoma metastases are often T1 hyperintense on MR due to melanin content
• Lymph nodes

image 1st nodes to be involved are usually regional lymph nodes with contiguous spread through lymphatic chains
image Metastatic nodes may enlarge or change in morphology (↑ enhancement, loss of fatty hilum)
• Liver

image Most common site of visceral organ involvement
image May be hypervascular on arterial phase and usually hypodense on venous phase
• Gastrointestinal tract

image Small bowel most common site (75% of cases)
image May present as lead point of small bowel intussusception
image Soft tumor that does not usually cause obstruction
• Gallbladder

image Melanoma is most common metastasis to gallbladder
• Kidney

image Can involve kidney, bladder, or collecting systems
image Unique predisposition for perirenal space
image Consider melanoma with isolated mass in perirenal space

TOP DIFFERENTIAL DIAGNOSES

• Leukemia and lymphoma
• Metastases from other primary tumors
• Primary GI malignancies
• Kaposi sarcoma

CLINICAL ISSUES

• Risk of metastasis correlates with depth of primary tumor into dermis
image
(Left) Axial CECT in a patient with known metastatic melanoma demonstrates mass-like wall thickening and aneurysmal dilatation image of 2 segments of colon, in keeping with bowel metastases.

image
(Right) Coronal volume-rendered CECT in the same patient demonstrates 3 different metastases image, with several others scattered throughout the small and large bowel (not shown). Lymphoma and GI stromal tumors can also cause similar aneurysmal dilatation.
image
(Left) Axial CECT in a patient with melanoma demonstrates a nodular hypervascular metastasis image in the small bowel causing proximal bowel obstruction image.

image
(Right) Axial CECT in the same patient demonstrates multiple other sites of nodular enhancing soft tissue image in the small bowel. Multifocal metastases to the bowel are not uncommon in melanoma.

TERMINOLOGY

Definitions

• Spectrum of metastatic lesions originating from known or occult malignant melanoma

IMAGING

General Features

• Best diagnostic clue

image Multiple “bull’s-eye” lesions of variable size in GI tract of patient with history of melanoma
• Location

image Unique predisposition for metastatic disease to unusual locations (gallbladder, small bowel, spleen, subcutaneous soft tissues, etc.) 

– Can metastasize to nearly any location and may have an isolated metastasis in atypical location
– Distant metastases depend on site of primary tumor

image Lower extremity melanomas often spread to pelvis
image Ocular melanomas frequently spread to liver
image Most common sites of metastases: Skin, lymph nodes (75%), lung (70%), liver (58%), CNS (54%), GI tract (40%)
image Most common sites in abdomen: Liver and small bowel
• Morphology

image Typically multiple, in any site of body
image Well-circumscribed, spherical or oval
image Nodule, plaque, polypoid mass
image “Bull’s-eye” or “target” lesion (central ulceration)

Imaging Recommendations

• Best imaging tool

image PET/CT (from vertex through feet) with diagnostic CECT for total body screening

– Sensitivity and specificity are ↑ by simultaneous interpretation of diagnostic quality CT
– Melanoma may not be FDG avid or may be misinterpreted as normal bowel or kidney on PET
• Protocol advice

image Multiphase CECT: Melanoma may be hypervascular and metastases may not be visualized on monophasic CECT

Radiographic Findings

• Radiography

image Rarely, calcification may be seen in hepatic lesions

CT Findings

• Lymph nodes

image First nodes to be involved are usually regional lymph nodes with contiguous spread through lymphatic chains

– Careful assessment necessary of lymph node stations adjacent to primary tumor
– Abdominal nodal involvement in 30% of cases
image Metastatic nodes may enlarge or change in morphology (↑ enhancement, loss of fatty hilum, irregular margins)

– Involved lymph nodes may enlarge and bleed
– Rarely necrotic with peripheral enhancement
• Liver

image Most common site of visceral organ involvement

– Particularly common with ocular melanoma, and can occur years after initial diagnosis
image Single or multiple lesions of variable size ± calcification

– May be hypervascular on arterial phase
– Most (86%) lesions hypodense on portal venous phase
image Rim enhancement in lesions with central necrosis
image Subcapsular hematoma may result from spontaneous bleeding of hepatic metastases
• Gastrointestinal tract

image Can involve any portion of GI tract, but small bowel is most common site (75% of cases)
image Can present with a single or multiple lesions, often with central necrosis or ulceration
image May lead to aneurysmal dilation of bowel lumen
image Predilection for antimesenteric border of small bowel
image May present as lead point of small bowel intussusception
image Esophagus

– Very rare lesion
– Bulky soft-tissue mass with esophageal dilatation upstream
– More common in distal 1/2
image Stomach

– Sessile or pedunculated intraluminal soft-tissue masses ± “target” appearance
image Duodenum

– Multiple sessile intramural or intraluminal masses, ± “target” appearance, ± fold thickening
image Small bowel

– Single or multiple intramural or intraluminal soft-tissue masses; ± extraluminal component
– Central necrosis (“target” appearance)
image Colon

– Single or multiple “target” lesions ± wall thickening, may simulate diverticulitis

image Due to eccentric wall thickening and infiltration of pericolonic fat
image Soft tumor that does not usually cause obstruction
• Mesenteric involvement

image Mesentery and omentum are often both involved
image Single or multiple nodules of variable size with peritoneal/omental stranding, nodularity, and ascites
image Melanoma should be considered with large solitary peritoneal soft-tissue mass without known primary
• Gallbladder

image Melanoma is most common metastasis to gallbladder

– Seen in 15% of patients (according to 1 series)
image Small, flat, subepithelial nodule gradually progresses to discrete polypoid mass
• Pancreas

image Peripancreatic nodes may simulate pancreatic mass
image Single or multiple enhancing nodules on CECT
image May be hypervascular on arterial phase and mimic neuroendocrine tumor
• Spleen

image Melanoma is common source of metastasis to spleen
image Seen in 30% of cases according to 1 report
image Multiple ill-defined low-attenuation lesions or well-defined “cystic” lesions (usually with solid component) 

– Single or multiple
– Homogeneous hypodense lesion may mimic cyst, but usually shows enhancement and solid component on CECT and US
• Kidney

image 3rd most common metastasis to kidney (after lung/breast cancer)

– Seen in 35% of cases
image Unique predisposition for perirenal space 

– Large isolated mass in perirenal space should prompt consideration of melanoma
– Can involve kidney, bladder, or collecting systems
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