Atypical findings of small intestinal adenocarcinoma with mesenteric extension

Abstract

Primary small intestinal cancer is a rare malignancy, accounting for 0.1%-0.3% of all gastrointestinal cancers. Its nonspecific presentation often delays diagnosis and worsens prognosis. This case report presents a patient with small intestinal cancer exhibiting mesenteric invasion and atypical features. We emphasize that mesenteric invasion is a rare finding, and the achieved 5-year recurrence-free survival in a Stage ⅡB small intestinal adenocarcinoma represents an exceptionally favorable outcome. The patient was a 78-year-old female who was referred to our hospital with a chief complaint of anorexia, vomiting, and abdominal pain. A palpable lower abdominal mass and intestinal obstruction were identified. Detailed evaluation confirmed small intestinal cancer with mesenteric metastasis. Laparotomy revealed a mass located in the small intestinal mesentery, encircled by folded small intestine. The mass demonstrated strong adherence to both the sigmoid colon and bladder walls. Surgical resection was performed, including excision of the mass, partial sigmoid colon resection, and partial bladder resection. Histopathological analysis confirmed a neoplasm of the small intestine. The patient received postoperative adjuvant chemotherapy with FOLFOX and remains alive without recurrence 5 years postoperatively. Small intestinal adenocarcinoma with mesenteric invasion is a rare finding and may present with vague symptoms and mimic other pathologies. Early use of imaging and multidisciplinary management are crucial for achieving favorable outcomes.

Introduction

Primary small intestinal cancer is a rare malignancy, comprising approximately 0.1%-0.3% of all gastrointestinal cancers [1]. The prognosis is generally poor with the 5-year survival rates by stage are as follows: Stage I (50%-60%), Stage II (40%-55%), Stage III (10%-40%), and Stage IV (3%-5%) [1,2]. Small intestinal cancer, particularly of the jejunum and ileum, is difficult to diagnose early due to nonspecific symptoms, often leading to presentation at advanced stages. Cancers of the jejunum and ileum are typically identified at more advanced stages once symptoms appear, whereas duodenal cancer is often detected incidentally. Furthermore, the mesenteric invasion observed in this case is a rare finding. This report presents a case of small intestinal cancer with mesenteric invasion and atypical clinical findings. The purpose of this report is not only to demonstrate the rare pathology of mesenteric invasion but also to serve as an example of successful radical resection and multidisciplinary adjuvant chemotherapy, resulting in a favorable long-term outcome (5-year recurrence-free survival).

Case presentation

The patient is a 78-year-old female with a primary complaint of anorexia, accompanied by vomiting and abdominal pain. The patient had a 40-year history of hypertension and dyslipidemia. The current illness began 2 months prior with anorexia, constipation, and diarrhea. The patient was referred to our department for further assessment and management due to persistent nausea, vomiting, abdominal pain, and worsening diarrhea. Physical examination revealed a palpable mass in the lower abdomen. The palpable mass in the lower abdomen was fist-sized, smooth, elastic, firm, and moderately mobile. Complete blood count indicated mild anemia (hemoglobin 9.3 g/dL). C-reactive protein (CRP) was elevated at 2.2 mg/dL, suggesting inflammation. Tumor markers were CEA 1.8 ng/mL and CA19-9 974.2 U/mL.

A supine position abdominal radiography showed small bowel dilatation and an upright position radiography showed the air-fluid levels, leading to a diagnosis of intestinal obstruction (Fig. 1). Abdominal contrast-enhanced CT (Ioversol 350, a nonionic contrast agent 45mL, arterial phase) revealed the presence of 2 irregular masses [4] (Fig. 2). Taking a look at the right-sided mass, the mass with an irregular shape and a long diameter of approximately 60 mm was detected on the right side of the pelvic cavity (Figs. 2A,C,D). This mass contained air (Fig. 2A). The small intestine encircled this mass, with indistinct margins between the mass and the small intestinal wall (Fig. 2A and D). One segment of the small intestinal wall adjacent to this right mass appeared thickened and displayed earlier and more prominent contrast enhancement compared with the surrounding walls (Fig. 2C and D). Secondly, the left-sided mass, measuring 65 mm, was observed on the left side of the pelvic cavity. The left mass partially contacted the sigmoid colon and bladder (Fig. 2B-D). Both masses showed peripheral contrast enhancement, though the interior showed insufficient enhancement, likely representing necrosis. The small intestine at the mass inlet showed slight dilatation and formed a bicuspid configuration. CT after Following gastrointestinal contrast medium administration (CT images obtained after oral Diatrizoate, iodinated contrast medium 100 mL) revealed contrast medium within the small intestine lumen adjacent to the mass in the pelvic cavity. However, no contrast medium was detected entering the mass (Fig. 3A and B). MRI (gadoteridol, macrocyclic nonionic MRI contrast agent 8mL) findings demonstrated a sizable mass with mildly hypo intense signals with heterogeneous margins on T2-weighted images. Diffusion-weighted images exhibited high signal intensity with reduced Apparent Diffusion Coefficient (ADC) values, and contrast-enhanced T1-weighted images showed enhancement. The mass was sizable and exhibited internal necrosis (Fig. 4A-E). Internal signals on T2-weighted imaging were low, with no diffusion restriction or enhancement seen on contrast-enhanced T1-weighted sequences. ¹⁸F–FDG-PET/CT revealed fluorodeoxyglucose F18uptake at the tumor margins, with a maximum standardized uptake value (SUV max) of 11.96. A portion of the mass interior lacked FDG uptake (Fig. 5). The upper and lower endoscopy revealed adenomatous polyps in the colon. Based on these findings, the tumor was diagnosed as small intestinal cancer with mesenteric invasion or perforation into the mesentery. Clinical stage was determined as cT4 (SI: mesenteric) N0M0, Stage IIB (UICC) [5].

Fig. 1.

Abdominal radiography images. (A) Supine position. Gas is present in the dilated small intestine (black arrows). (B) Upright position. Gas in the dilated small intestine forms air-fluid levels (black arrowheads).

Fig. 2.

Contrast enhanced CT images. (A) An irregularly shaped mass is present in the right pelvic cavity (white arrow), containing air density. Contrast enhancement is seen only at the margins. The small intestine proximal to the mass is mildly dilated (white arrowheads). (B) Another mass with irregular shape and contrast enhancement at its margins is also noted on the right side within the pelvis (white arrow). (C) The wall of the small intestine (white arrow) adjacent to the irregular mass (white arrow) is thickened. (D) A coronal image. Two irregular masses are present (white arrows), one of which is adjacent to the bladder (white arrowhead).

Fig. 3.

CT images with oral contrast agent administration. (A) Coronal image. (B) Sagittal image. No contrast agent is detected within the mass (white arrows).

Fig. 4.

MR images. Each image shows masses (white arrows) within the pelvis. (A) T2-weighted image. Irregular masses show heterogeneous low signal intensity. (B) Diffusion-weighted image. Peripheral of the masses show high signal intensity. (C) Apparent diffusion coefficient (ADC) map (b = 800). Peripheral of the masses show low value. (D) Fat suppressed T1-weighted image. The masses show low signal intensity. (E) Contrast enhanced fat suppressed T1-weighted image. Peripheral of the masses show high signal intensity. The central regions are not enhanced. These images suggest peripheral cellular proliferation at the masses and central necrosis.

Fig. 5.

FDG PET/CT image. FDG uptake is observed at the masses (white arrows) margin. It demonstrates peripheral metabolic activity with lack of metabolic activity within the lesion.

Differential diagnoses included malignant lymphoma and GIST (gastrointestinal stromal tumor) [4]. The presence of an irregular shape and presentation as a large mass suggested lymphoma or GIST. However, the radiological features suggestive of adenocarcinoma, such as bowel wall invasion (thickened wall and prominent enhancement) and the presence of internal necrosis, were key factors for distinguishing it from GIST (which is typically spherical and well-demarcated) and malignant lymphoma (for which large internal necrosis is atypical).

Surgical findings revealed a mass located in the mesentery of the small intestine, enveloped by small bowel loops (Fig. 6A). It was strongly adherent to the sigmoid colon and bladder, which were clumped together (Fig. 6B). Colectomy included resection of the mass, partial sigmoid colon resection, and partial bladder resection [6]. The resected mass, mainly located within the small intestinal mesentery, measured approximately 10 × 8 cm. As for the clarification of mass count, the 2 masses seen separately on CT (60 mm and 65 mm) were found surgically to be a single large mesenteric mass (10 × 8 cm) with a bipartite appearance. This complex presentation confirms that the pathology represents a single, locally advanced tumor complex, likely due to strong adherence and coalescence of the lesions over time, and no substantial discrepancy exists between the imaging and surgical findings [7]. The surrounding small intestine was densely adherent to the lesion (Fig. 6C). Three areas of the small intestinal mucosa showed submucosal tumor invasion, with 1 area displaying a 20 × 18 mm mucosal defect exposing tumor tissue (Fig. 6B and C). The mesenteric mass had a bipartite appearance and revealed a large grayish-white tumor partially invading the intestinal wall (Fig. 6D). Hematoxylin–eosin staining showed tumor cells with cord-like or poorly defined glandular structures (Fig. 6E). Immunohistochemistry was positive for AE1/AE3 and negative for calretinin, CD45, melan A, c-kit, and mesenchymal markers, supporting a diagnosis of poorly to moderately differentiated adenocarcinoma. The tumor invaded the subareas of the sigmoid colon and the subperitoneal adipose tissue of the bladder. Coagulative necrosis was predominant.

Fig. 6.

Surgical and histopathological findings. (A) Intraoperative photograph. Preoperative imaging studies showed multiple masses, but it was a single tumor. (B) Resected specimen. A defect is observed in the small intestinal mucosa (white arrow). (C) Split view of the resected specimen. A defect is observed in the small intestinal mucosa, with a white mass visible immediately below the defect. (D) Sectioned image of the specimen. The white mass was thought to have extended from a defect in the small intestinal mucosa (white arrow) into the mesentery. The mass had infiltrated the bladder (white arrowhead) and sigmoid colon (black arrowhead). (E) Histopathological image (hematoxylin–eosin stain). Tumor cells exhibited cord-like or tubular structures.

Pathological staging revealed adenocarcinoma, INFb, ly1b, v1b, pn1b, cy0, UICC classification pT4 (Specific Invasion: small intestinal mesentery, sigmoid colon, bladder) pN0, cM0, pStage IIB. Radical resection was achieved [8].

Postoperative adjuvant chemotherapy with 9 courses of FOLFOX was administered over 7 months, following the protocol for colorectal cancer [3,9]. The patient has remained recurrence-free for 5 years following surgery.

Discussion

According to a large cohort study comprising 4995 cases of duodenal and small intestinal cancer (excluding papillary cancer), conducted by the National Cancer Data Base (NCDB) in the United States, small intestinal cancer accounts for approximately 2% of digestive cancers and 1% of related deaths, and is thus considered a rare malignancy [3]. Duodenal cancer is often detected incidentally during upper gastrointestinal endoscopy, whereas cancers of the jejunum and ileum are typically identified at more advanced stages once symptoms appear. Most cases occur in the duodenum and proximal jejunum; ileal cases, as in the present report, are comparatively rare.

Small intestinal cancer is frequently asymptomatic in its early stages. Symptoms indicative of gastrointestinal bleeding—such as anemia, hemorrhage, melena, and positive fecal occult blood tests—commonly prompt consultation with a physician. In recent years, the widespread adoption of small intestinal capsule endoscopy and small bowel endoscopy has markedly improved the detection of early-stage disease. This technological progress represents a promising advancement in gastrointestinal diagnostics. Obstructive symptoms generally occur with increasing tumor size. Given that most macroscopically visible tumors are of the ring stenosis type, small intestinal cancer is more likely than other small intestinal tumors to cause obstruction. In this case, the carcinoma likely originated from a mucosal defect and subsequently spread into the small intestinal wall and mesentery, later infiltrating adjacent structures, including the sigmoid colon and bladder. Consequently, the patient remained asymptomatic for obstruction until the tumor had extended into surrounding tissues and formed a mass. Distinguishing the tumor from a submucosal mass or peritoneal dissemination was challenging, as evidenced by both CT and MRI findings.

Histopathological analysis revealed coagulative necrosis within the tumor, indicating that rapid growth had compromised intratumoral blood flow. Contrast-enhanced CT demonstrated an oligometastatic mass, while FDG-PET and MRI findings indicated a developed mass with internal necrosis. The difficulty in early diagnosis often means small intestinal cancer presents at advanced stages. In this case, the carcinoma likely originated from a mucosal defect and subsequently spread into the small intestinal wall and mesentery, later infiltrating adjacent structures, including the sigmoid colon and bladder.

Differential diagnoses included malignant lymphoma and GIST. However, malignant lymphoma is atypical for internal necrosis, and GIST usually presents as a spherical, well-demarcated mass, although internal necrosis may be observed [4]. Conversely, small intestinal cancers of the jejunum and ileum are characteristically annular, stenotic tumors with circumferential invasion. Mesenteric invasion by small intestinal cancer remains uncommon. In the aspect of the quantification of rarity, pT4 mesenteric invasion, small intestinal cancers of the jejunum and ileum are characteristically annular, stenotic tumors. Mesenteric invasion by small intestinal cancer remains uncommon [5].

The patient underwent diagnostic imaging, including CT and both upper and lower gastrointestinal endoscopy. These investigations facilitated scheduling for surgical intervention, contingent on ongoing evaluation and a 2-month waiting period. Although small intestinal cancer was initially suspected, conclusive diagnostic evidence was lacking. Accordingly, the therapeutic approach prioritized diagnostic confirmation over immediate treatment. Surgical resection involves excision of the affected bowel segment along with lymphadenectomy [7,8]. For sizable lesions, it is recommended to maintain a margin of ≥5 cm on the anorectal side of the tumor to reduce postoperative margin recurrence risk and to dissect ≥9 lymph nodes to improve survival outcomes. In the present case, adequate resection margins were achieved, and the invaded area was excised, indicating that radical resection was successfully performed.

A curative resection was achieved in this case, followed by postoperative adjuvant chemotherapy aimed at recurrence control and prognostic improvement. As per the Colorectal Cancer Treatment Guidelines for Physicians 2024 Edition [9], the standard regimen at diagnosis comprises oxaliplatin-based combination therapy (FOLFOX or CAPOX) administered for 6 months. In this case, FOLFOX was delivered over 9 cycles due to tumor invasion into the small intestinal mesentery, sigmoid colon, and bladder, alongside evidence of vascular infiltration. Furthermore, microsatellite instability (MSH-H) is observed in 5%-45% of small intestinal cancers, often accompanied by elevated PD-1 and PD-L1 expression. The effectiveness of pembrolizumab, a PD-L1 antibody, has been demonstrated, and the benefits of immune checkpoint inhibitors are increasingly recognized [9].

In Japan, the “Small Intestinal Malignancy Project Study” was initiated in 2019 by the Colorectal Cancer Study Group. This multicenter, multi-case investigation aims to establish a standardized “Small Intestinal Cancer Treatment Guideline." Historically, formal treatment guidelines for small intestinal cancer were lacking. However, the National Comprehensive Cancer Network (NCCN) has developed a comprehensive guideline for the treatment of small intestinal cancer, also released in 2019 [8]. This advancement is of considerable significance, offering essential guidance to clinicians and improved care strategies for patients.

To comment on the exceptional 5-year survival, the pathological stage in this patient was pT4 N0 (Stage IIB), indicating invasion into adjacent organs [7]. Stage II small intestinal cancer generally has a reported 5-year survival rate of 40%-55%. The achievement of 5-year recurrence-free survival in a pT4 tumor, despite multiorgan invasion, represents an exceptionally favorable outcome. This favorable 5-year outcome serves as a strong validation of the importance of multidisciplinary management, including successful radical resection of the primary tumor and involved adjacent organs, followed by adjuvant FOLFOX chemotherapy [10]. This outcome is particularly notable considering the aggressive nature implied by the vascular infiltration and advanced T status.

Furthermore, given the rarity of small intestinal adenocarcinoma, we must consider the possibility of multiple primary malignancies (MPMs), particularly since the patient also presented with adenomatous polyps in the colon [11].

Conclusions

This report describes a case of small intestinal cancer with extensive mesenteric invasion and atypical clinical presentation. Advances in imaging and surgical intervention enabled curative resection. Early detection remains challenging; however, advances in imaging and surgical intervention enabled curative resection. The case emphasizes the need for vigilance in evaluating nonspecific gastrointestinal symptoms in older adults. We emphasize the success of multidisciplinary management.

Teaching points

Small intestinal cancer may present with an irregular shape, invasion of adjacent organs, and internal necrosis. FDG-PET and MRI may assist in assessing the internal characteristics of the tumor.

When encountering an irregular mesenteric mass with small intestinal involvement, small intestinal adenocarcinoma should be included in the differential diagnosis, despite its rarity, given its nonspecific presentation and the potential for favorable long-term outcomes.

Ethical approval

This study was approved by the Ethics Committee of our institution.

Patient consent

Informed consent was obtained for the case report to be published.