Small bowel metastasis represents spread of other organ primaries to the small bowel and is the most common cause of small bowel malignant tumors (50-70%). Melanoma, lung, breast, colon, and renal cancers most frequently metastasize. Melanoma metastases are hypervascular with prominent arterial enhancement and bull's-eye (target) sign — this pathognomonic finding represents a submucosal nodule with central ulceration. Spread routes are hematogenous (most common), peritoneal seeding, direct invasion, and lymphatic. On CT, single or multiple nodular/polypoid intraluminal masses, wall thickening, aneurysmal dilatation, or circumferential involvement are observed. Complications include intussusception, obstruction, hemorrhage, and perforation. PET-CT is used for staging and treatment response assessment. Prognosis is generally poor — small bowel metastasis reflects advanced disseminated disease.
Age Range
40-80
Peak Age
60
Gender
Equal
Prevalence
Uncommon
Small bowel metastasis develops through four main routes: (1) Hematogenous spread — most common in melanoma, lung, and breast carcinoma; implants into the submucosa via arterial blood and forms submucosal nodules. Melanoma's submucosal location preference is attributed to the neural crest origin of melanocytes and tropism for mesenteric vasculature. (2) Peritoneal seeding — common in ovarian, colon, and gastric carcinoma; free tumor cells are carried by peritoneal fluid and implant on serosal surfaces. (3) Direct invasion — direct extension of adjacent organ tumors into the small bowel wall. (4) Lymphatic spread — retrograde spread from mesenteric lymph nodes. The bull's-eye (target) sign results from the submucosal tumor nodule developing central ischemic necrosis and ulceration — peripheral viable tumor enhances while the central necrotic area does not, and this contrast difference creates the target appearance. Aneurysmal dilatation is explained by tumor invasion of the muscularis propria disrupting wall tone and causing luminal dilatation.
Hypervascular submucosal nodule + central ulceration in the small bowel wall on arterial phase = bull's-eye (target) appearance. Pathognomonic for melanoma metastasis. Peripheral viable tumor enhances intensely while central necrotic/ulcerative area does not — this contrast difference creates the target appearance.
In the arterial phase, melanoma metastasis appears as a hypervascular submucosal nodule in the small bowel wall, forming a bull's-eye (target) appearance with a central ulceration area. Peripheral viable tumor tissue shows intense arterial enhancement while the central necrotic/ulcerative area does not enhance. This finding is pathognomonic for melanoma metastasis. Nodules are usually 1-5 cm in diameter, well-marginated, and may show intraluminal or transmural extension. Multiple nodules may be found in different small bowel segments.
Report Sentence
A submucosal nodule measuring approximately ___ cm in the small bowel wall is seen with intense arterial enhancement and a central low-attenuation area consistent with ulceration (bull's-eye sign); metastasis is considered given the known melanoma history.
In the portal venous phase, small bowel metastases appear as multiple intraluminal polypoid or annular masses. Different morphological patterns: (1) polypoid/nodular — intraluminal protruding mass, (2) infiltrative/annular — circumferential wall thickening with luminal narrowing, (3) ulcerative — irregular mass with cavitation and ulceration, (4) eccentric — mass originating from one side of the wall. Dilated small bowel loops proximally indicate obstruction. Mesenteric lymphadenopathy and peritoneal nodules may accompany.
Report Sentence
Multiple intraluminal polypoid/nodular masses are seen in small bowel loops with obstruction findings at the ___ level; metastatic disease is considered given the known malignancy history.
Aneurysmal dilatation of the small bowel segment showing metastatic involvement — luminal dilatation is observed without obstruction. This finding results from tumor invasion of the muscularis propria disrupting peristaltic activity and causing loss of wall tone. Most commonly seen in melanoma and lymphoma metastases. Irregular thickening and enhancing nodules accompany the dilated segment wall. Proximal and distal bowel segments are normal caliber — unlike mechanical obstruction.
Report Sentence
Aneurysmal dilatation of approximately ___ cm length small bowel segment at the ileum/jejunum level is seen with wall thickening and nodular enhancement; no mechanical obstruction findings.
A metastatic nodule may act as a lead point creating intussusception. On CT, characteristic 'target' or 'sausage' sign — telescoped bowel loops, mesenteric fat and vessels drawn into the intussusception (mesenteric fat sign). Lead point mass appears as an enhancing nodule at the apex of the intussusceptum. In adults, intussusception is associated with underlying organic pathology (malignancy) in 60-90% of cases.
Report Sentence
Small bowel intussusception is seen at the ___ level with an enhancing lead point mass measuring approximately ___ cm at the apex of the intussusceptum; should be evaluated for malignancy as adult intussusception.
On DWI, small bowel metastases show high signal with low values on the ADC map. Restricted diffusion reflects high cellularity. MR enterography is complementary to CT for detecting metastatic nodules — especially for small submucosal lesions and mucosal pathology. When evaluated with post-contrast sequences, it provides information about tumor viability. ADC value increase in treatment response monitoring indicates treatment efficacy.
Report Sentence
Nodules showing focal diffusion restriction in the small bowel wall are seen on DWI with low values on the ADC map — consistent with metastatic involvement.
On PET-CT, small bowel metastases show focal or multifocal increased FDG uptake. Melanoma metastases are typically intensely FDG-avid (SUVmax 5-15). PET-CT is superior to CT for detecting small bowel metastases — especially for small submucosal lesions. Differentiation from physiological bowel FDG uptake is necessary — focal, asymmetric, and anatomically correlated uptake is pathological. PET-CT also detects occult metastases in other organs during staging.
Report Sentence
On PET-CT, ___ foci of focal increased FDG uptake are seen in small bowel loops (SUVmax: ___); metastatic involvement is considered given the known malignancy history.
Criteria
Known melanoma history, hypervascular submucosal nodules, bull's-eye sign, prominent arterial enhancement.
Distinct Features
High signal on T1 MRI due to melanin content, intense arterial enhancement on CT, intussusception is common complication. May present with GI bleeding.
Criteria
Involvement starting from serosal surface, accompanied by peritoneal carcinomatosis, ovarian/colonic/gastric primary.
Distinct Features
CT shows serosal surface nodular involvement, omental cake, ascites, mesenteric nodules. Submucosal bull's-eye sign not seen.
Criteria
Direct extension from adjacent organ tumor (colon, pancreas, kidney). Accompanied by fat plane loss.
Distinct Features
CT shows fat plane loss between primary tumor and small bowel, focal wall thickening, single location. Multicentricity not expected.
Distinguishing Feature
Lymphoma shows aneurysmal dilatation but usually homogeneous wall thickening; metastasis nodular/polypoid and hypervascular (melanoma). Mesenteric sandwich sign in lymphoma.
Distinguishing Feature
Carcinoid single small hypervascular mass + desmoplastic mesenteric reaction (stellate calcification); metastasis multiple, bull's-eye sign, and known primary.
Distinguishing Feature
GIST eccentric, exophytic growth pattern, usually single; metastasis intraluminal, multiple. GIST c-KIT/DOG1 positive.
Distinguishing Feature
Adenocarcinoma single, annular, stenosing mass, proximal obstruction; metastasis multiple, polypoid, known primary history.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
specialist-referralSmall bowel metastasis reflects advanced disseminated disease and prognosis is generally poor. Acute complications (obstruction, hemorrhage, perforation, intussusception) may require surgical intervention. Treatment includes systemic chemotherapy/immunotherapy directed at the primary tumor and palliative surgical/endoscopic intervention. Immunotherapy (checkpoint inhibitors) response rates have increased in melanoma metastases. PET-CT is used for staging and treatment response monitoring.
Small bowel metastases occur in advanced disease and carry a poor prognosis. GI bleeding, obstruction, and perforation may require surgical intervention. PET-CT is important for staging and follow-up.