Small bowel adenocarcinoma is the most common primary malignant tumor of the small intestine, accounting for 3-5% of all gastrointestinal malignancies. It most frequently occurs in the duodenum and proximal jejunum. Histologically, it arises from mucosal glandular epithelium and typically demonstrates an annular (circumferential) growth pattern causing luminal narrowing and obstruction. The mean age at diagnosis is 60-70 years with slight male predominance. Crohn's disease, celiac disease, familial adenomatous polyposis (FAP), and Lynch syndrome are significant risk factors. Prognosis is generally poor because diagnosis is often made at an advanced stage; the 5-year survival rate is approximately 30-40%. CT enterography and MR enterography are the primary diagnostic modalities; endoscopy and EUS provide additional value for duodenal lesions.
Age Range
45-85
Peak Age
65
Gender
Male predominant
Prevalence
Rare
Small bowel adenocarcinoma is a malignant neoplasm arising from mucosal glandular epithelium. The adenoma-carcinoma sequence operates similarly to colorectal cancer; APC, KRAS, TP53, and mismatch repair gene mutations play a role in pathogenesis. In Crohn's disease, the chronic inflammation → dysplasia → carcinoma progression has been described; particularly long-standing disease (>8 years) in the ileal segment increases risk. In celiac disease, chronic villous atrophy and increased cell turnover trigger carcinogenesis. The tumor demonstrates transmural growth reaching the serosa and metastasizes to mesenteric lymph nodes, liver, and peritoneum. The annular growth pattern causes progressive luminal narrowing — this creates the 'apple core' appearance on CT enterography and produces upstream intestinal dilation. Due to the tumor's hypervascularity, it shows enhancement in the arterial phase; however, necrotic areas do not enhance and create a heterogeneous pattern.
Characteristic appearance on CT enterography where the annular tumor narrows the lumen and demonstrates 'overhanging edges' at both ends. Named because the tumoral narrowing resembles the core of a bitten apple. This finding is the most common morphological pattern in primary small bowel adenocarcinoma and parallels the similar finding in colorectal adenocarcinoma.
Focal, annular (circumferential) thickening of the small bowel wall on CT enterography — classic 'apple core' appearance. Wall thickness is generally >15 mm, creating significant luminal narrowing. Tumor margins are typically abrupt with 'overhanging edges.' On contrast-enhanced CT, moderate to prominent heterogeneous enhancement is seen in the arterial phase; necrotic areas remain hypodense. In duodenal location, luminal irregularity is more prominent with double-contrast effect.
Report Sentence
Focal annular wall thickening with luminal narrowing in the small bowel demonstrating heterogeneous arterial phase enhancement is consistent with primary small bowel adenocarcinoma.
Prominent intestinal dilation proximal to the tumor with an abrupt caliber change demonstrating a transition point on portal venous phase. Fluid and gas accumulation may be seen in the dilated segment. 'Small bowel feces sign' may be observed proximal to the obstruction — particulate intestinal content due to stasis and water reabsorption. Distal segments appear collapsed and decompressed.
Report Sentence
Proximal small bowel dilation due to focal wall thickening at the transition point is observed, consistent with mechanical obstruction findings.
Enlarged mesenteric lymph nodes (short axis >10 mm) with pathological enhancement adjacent to the tumor on portal venous phase. Lymph nodes acquire round morphology and lose hilar architecture. In advanced stages, retroperitoneal and para-aortic lymphadenopathy may also be present. Conglomerate lymph nodes may encase mesenteric vascular structures.
Report Sentence
Enlarged lymph nodes with pathological enhancement in the mesentery adjacent to the tumor are observed, consistent with lymphatic metastasis.
Focal mass with intermediate to high signal intensity in the small bowel wall on T2-weighted images. Tumor tissue appears mildly hyperintense compared to normal bowel wall. Necrotic areas demonstrate marked T2 hyperintensity, while desmoplastic/fibrotic components may be T2 hypointense. With distension provided by MR enterography, wall thickening and luminal narrowing are clearly visualized on T2 sequences.
Report Sentence
Focal wall thickening with heterogeneous signal intensity on T2-weighted images in the small bowel is observed, suspicious for small bowel neoplasm.
Marked diffusion restriction in the tumor area on diffusion-weighted imaging (DWI) — bright signal on high b-value images and low values on ADC maps. ADC values are typically <1.2 × 10⁻³ mm²/s. DWI provides additional value in detection of small bowel adenocarcinoma and differentiation from benign inflammatory thickening. Inflammatory thickening generally shows higher ADC values.
Report Sentence
Marked diffusion restriction (low ADC values) on DWI in the area of wall thickening is observed, consistent with a malignant process.
Irregularity of the tumor's serosal surface and increased density in peritumoral fat tissue (fat stranding) on delayed phase. Serosal penetration appears as blurring of extramural fat planes, reticular density increase, and focal fluid collections. In advanced stages, findings of peritoneal carcinomatosis (peritoneal nodules, omental caking, ascites) may be present. The delayed phase is most useful for evaluating serosal invasion and desmoplastic reaction.
Report Sentence
Peritumoral fat stranding and serosal surface irregularity around the tumor are observed, consistent with transmural invasion.
Marked FDG uptake in the tumor area on FDG PET-CT — SUVmax is typically >5-8. PET-CT provides superiority over CT in detecting distant metastases (liver, peritoneum, bone) and pathological lymph nodes, in addition to demonstrating metabolic activity of the primary tumor. Also used for treatment response evaluation. However, physiological intestinal FDG uptake may lead to false-positive results.
Report Sentence
A mass with marked metabolic activity increase (high SUVmax) on FDG PET-CT in the small bowel is observed, consistent with a malignant process.
Criteria
Adenocarcinoma located in the duodenum (D1-D4) — most common small bowel adenocarcinoma location (50-60%)
Distinct Features
In periampullary location, biliary and pancreatic duct obstruction (double duct sign), may present with jaundice. Endoscopic biopsy plays a key role in diagnosis. FAP-associated duodenal adenomas carry risk of malignant transformation.
Criteria
Adenocarcinoma located in the jejunum — second most common location (20-30%)
Distinct Features
Adenocarcinoma developing on celiac disease background is frequently jejunal in location. Obstruction symptoms are more prominent. CT enterography is the primary diagnostic modality; capsule endoscopy may provide additional information.
Criteria
Adenocarcinoma located in the ileum — least common location (10-15%)
Distinct Features
Adenocarcinoma developing on Crohn's disease background is frequently ileal in location. In Crohn-associated adenocarcinoma, the tumor may be hidden within a stricture, making diagnosis difficult. Long-standing Crohn's disease (>8 years) is a risk factor.
Criteria
Adenocarcinoma developing in the setting of long-standing Crohn's disease — usually ileal, in stricture segment
Distinct Features
New focal asymmetric wall thickening or worsening obstruction in an existing Crohn stricture should raise suspicion. Differentiation from inflammatory thickening is difficult — DWI and ADC mapping provide additional value. May be incidentally detected in surgical resection specimens.
Distinguishing Feature
Lymphoma typically shows diffuse wall thickening and aneurysmal dilation rather than annular narrowing; obstruction is rare because desmoplastic reaction is absent
Distinguishing Feature
GIST typically shows exophytic growth and luminal obstruction is rare; adenocarcinoma grows intraluminally/annularly and causes obstruction
Distinguishing Feature
Carcinoid shows small intraluminal polypoid lesion + prominent desmoplastic mesenteric mass (sunburst calcification); adenocarcinoma is characterized by larger annular wall thickening
Distinguishing Feature
Crohn's disease shows long-segment wall thickening, skip lesions, mural stratification, and fistula/sinus tracts; adenocarcinoma demonstrates focal short-segment narrowing and asymmetric thickening
Distinguishing Feature
Metastasis typically presents with multiple lesions, hematogenous spread pattern, and known primary malignancy; primary adenocarcinoma presents as a solitary annular lesion
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralUpon detection of small bowel adenocarcinoma, multidisciplinary tumor board evaluation is required. Primary treatment is surgical resection — segmental resection with wide clear margins and mesenteric lymph node dissection. Duodenal lesions may require Whipple procedure (pancreaticoduodenectomy). Adjuvant chemotherapy (FOLFOX regimen) is frequently administered. Palliative chemotherapy is given in metastatic disease. CT chest-abdomen-pelvis and PET-CT are recommended for staging.
Small bowel adenocarcinoma is an aggressive tumor that may be asymptomatic early. It is often advanced at diagnosis. Surgical resection is the primary treatment. Celiac disease, Crohn's disease, and FAP are risk factors.