Ileocecal intussusception secondary to poorly differentiated mucinous adenocarcinoma with focal signet ring cell component in a 15-year-old adolescent: a case report

Abstract

Background

Intussusception in adolescents is uncommon and more frequently associated with a pathological lead point than in infants and young children. Pediatric colorectal adenocarcinoma is exceedingly rare, and poorly differentiated mucinous adenocarcinoma with signet ring cell differentiation is particularly aggressive. We report a rare adolescent case presenting as ileocecal intussusception and highlight key diagnostic implications.

Case presentation: We report a 15-year-old boy who presented with intermittent abdominal pain for 10 days. Computed tomography revealed ileocecal intussusception, which was successfully reduced by pneumatic enema. Post-reduction ultrasonography identified a suspicious lesion in the ascending colon. Subsequent colonoscopy revealed a broad-based, firm, mucus-covered mass in the ascending colon near the ileocecal valve, and biopsy confirmed poorly differentiated mucinous adenocarcinoma with a focal signet ring cell component. The patient underwent right hemicolectomy with lymphadenectomy. Final pathology revealed pT3N2aM0 disease (AJCC 8th edition, stage IIIB) with retained mismatch repair protein expression, suggesting microsatellite stability. The patient received adjuvant CAPOX chemotherapy and remains disease-free at 7-month follow-up.

Conclusions

Successful reduction of adolescent intussusception should not end the diagnostic workup. Systematic post-reduction evaluation is essential to identify a pathological lead point, and normal tumor markers should not provide false reassurance. Timely tissue diagnosis and multidisciplinary oncologic management are critical.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-026-06815-5.

Background

Intussusception is a common cause of intestinal obstruction in infancy and early childhood and is usually idiopathic. In contrast, intussusception in older children and adolescents is uncommon and more frequently associated with a pathological lead point, including neoplasms, Meckel’s diverticulum, polyps, or lymphoma [1]. Recent epidemiologic data support this age gradient: pediatric intussusception peaks in children aged 1–4 years, whereas adolescents aged 10–19 years account for < 2% of all intussusception presentations in a nationwide cohort [2]. Reviews of tumor-related pediatric intussusception further suggest an older age distribution (mean age approximately 5.5 years), with most intestinal tumor-associated cases occurring in children > 2 years [3].

Colorectal adenocarcinoma in the pediatric and adolescent population is exceedingly rare (< 1% of pediatric malignancies) [4, 5]. Poorly differentiated tumors with mucinous features are particularly aggressive and often present at advanced stage. According to the WHO classification, mucinous adenocarcinoma is defined by extracellular mucin comprising at least 50% of tumor volume, whereas signet ring cell carcinoma requires > 50% signet ring cells [6]. We report a 15-year-old adolescent with ileocecal intussusception as the initial presentation of ascending colon poorly differentiated mucinous adenocarcinoma with a focal signet ring cell component.

Case presentation

Clinical presentation

A 15-year-old boy presented to our emergency department with a 10-day history of intermittent periumbilical and right lower quadrant abdominal pain. The pain was colicky in nature and occurred several times per day. The patient denied associated symptoms including fever, vomiting, hematochezia, melena, weight loss, anorexia, or changes in bowel habits. His past medical and surgical history was unremarkable. There was no family history of colorectal cancer, inflammatory bowel disease, or polyposis syndromes.

Physical examination and initial investigations

On physical examination, vital signs were stable with normal temperature, heart rate, blood pressure, and respiratory rate. Abdominal examination revealed mild tenderness in the right lower quadrant without guarding, rebound tenderness, or peritoneal signs. No palpable mass was detected. The remainder of the physical examination was unremarkable. Laboratory investigations including complete blood count, liver function tests, renal function tests, and serum electrolytes were within normal limits. High-sensitivity C-reactive protein was elevated at 15.2 mg/L (reference range: 0–3 mg/L), whereas procalcitonin was within the normal range at 0.08 ng/mL (reference range: <0.5 ng/mL).

Imaging findings

Given the patient’s age, prolonged symptoms (10 days), and the need to exclude a broad range of intra-abdominal pathologies—such as complicated appendicitis or a retroperitoneal mass—contrast-enhanced computed tomography (CT) was selected as the initial imaging modality. The scan was performed with 4-mm slice thickness and intravenous meglumine diatrizoate contrast, without oral contrast. CT demonstrated an ileocecal intussusception (approximately 7 cm in length); notably, no signs of high-grade bowel obstruction, perforation, or free intraperitoneal fluid were identified (Fig. 1A, B).

Fig. 1.

Radiological imaging findings. A, B Contrast-enhanced abdominal computed tomography demonstrating an ileocecal intussusception (approximately 7 cm in length) with a classic bowel-within-bowel configuration (red arrow). C Post-pneumatic enema reduction radiograph confirming successful reduction with complete resolution of the intussusception (red arrow). D, E, F Post-reduction ultrasonography identifying a heterogeneous solid lesion (approximately 4 cm in maximal diameter) in the ascending colon with increased intralesional vascularity on color Doppler imaging (E, F), highly suggestive of a pathological lead point (red arrows)

Initial management

Based on the imaging findings, pneumatic enema reduction was performed under fluoroscopic guidance. The reduction was successful, with rapid resolution of the patient’s abdominal pain (Fig. 1C). Given the patient’s age and the atypical presentation for idiopathic intussusception, post-reduction ultrasonography (US) was performed as per our institutional protocol for adolescent intussusception.

Post-reduction evaluation

Post-reduction US examination identified a heterogeneous solid lesion in the ascending colon region, measuring approximately 4 cm in maximal diameter and suspicious for a pathological lead point (Fig. 1D). The lesion demonstrated mixed echogenicity with irregular borders and increased vascularity on color Doppler imaging (Fig. 1E, F). Serum tumor markers (CEA, CA19-9, CA125, and AFP), obtained after lesion detection as part of an expanded workup for a pathological lead point, were within normal limits. Retrospective review suggested that the lesion was likely obscured on the initial CT by the intussusception complex and bowel wall edema.

Endoscopic evaluation and histopathology

Based on the US findings, colonoscopy was performed 72 h after reduction once the patient was clinically stable. Colonoscopy revealed a broad-based, cauliflower-like, and firm mucus-covered mass in the ascending colon near the ileocecal valve, approximately 4 cm in maximal diameter. The lesion exhibited an irregular, friable surface with areas of ulceration and partial circumferential involvement (Fig. 2A, B). The lesion appeared to arise from the medial wall of the ascending colon and extended toward the ileocecal valve. Multiple cold forceps biopsies were obtained from different areas of the lesion. Histopathological examination of the biopsy specimens confirmed poorly differentiated adenocarcinoma with predominantly mucinous architecture and a focal signet ring cell component (Fig. 2C, D). The tumor cells demonstrated marked nuclear pleomorphism and increased mitotic activity. Large pools of extracellular mucin dissecting through the tumor accounted for more than 50% of the tumor volume. Scattered signet ring cells with intracytoplasmic mucin and eccentric nuclei were identified, comprising approximately 10–15% of the tumor cell population.

Fig. 2.

Endoscopic and histopathological findings. A, B Colonoscopy showing a broad-based, cauliflower-like, and firm mucus-covered mass in the ascending colon near the ileocecal valve. The lesion exhibits an irregular, friable surface with areas of ulceration and partial circumferential involvement. C, D Representative hematoxylin and eosin staining (magnification: C, ×100; D, ×400) showing poorly differentiated adenocarcinoma with a predominantly mucinous architecture, characterized by large pools of extracellular mucin and a focal signet ring cell component (red arrow) with intracytoplasmic mucin and eccentric nuclei

Surgical management

After discussion at a multidisciplinary tumor board (MDT) involving pediatric surgeons, pediatric oncologists, pathologists, and radiologists, comprehensive staging workup revealed no evidence of distant metastases, and curative-intent surgery was recommended. However, the patient’s family elected to proceed with definitive surgical management at another hospital. Operative details and the final pathology report were obtained from the receiving institution. The patient subsequently underwent open right hemicolectomy with en bloc resection of the terminal ileum, cecum, ascending colon, and hepatic flexure, along with regional lymphadenectomy including the ileocolic, right colic, and middle colic lymph node basins.

Final pathological findings

The resected specimen measured 22 cm in total length (7 cm of terminal ileum and 15 cm of colon). A 4 × 5 cm exophytic, cauliflower-like mass was identified in the ascending colon, protruding into the lumen. Grossly, the tumor was circumferential and ulcerated, with raised, irregular margins. Final histopathological examination confirmed a poorly differentiated mucinous adenocarcinoma with a focal signet ring cell component. The tumor invaded through the muscularis propria into the subserosa without penetration of the visceral peritoneum (pT3). Lymphovascular invasion was present in the submucosa, whereas no perineural invasion was identified. A total of 37 regional lymph nodes (ileocolic, right colic, and middle colic basins) were retrieved, of which six harbored metastatic adenocarcinoma (pN2a). Both the proximal (ileal) and distal (colonic) resection margins were free of carcinoma, with adequate clearance distances of 5 cm and 8 cm, respectively. Immunohistochemistry (IHC) demonstrated retained nuclear expression of all four mismatch repair (MMR) proteins (MLH1, PMS2, MSH2, and MSH6), consistent with microsatellite-stable (MSS) biology. The Ki-67 labeling index was approximately 50%, indicating high proliferative activity. Additional IHC findings showed diffuse strong membranous expression of Trop2 and positive expression of Claudin18.2. CDX2 was positive. CD31 highlighted vascular endothelium, and S-100 highlighted neural elements. According to the American Joint Committee on Cancer (AJCC) 8th edition staging system, the final pathological stage was pT3 pN2a cM0, corresponding to Stage IIIB disease.

Postoperative course and adjuvant treatment

The postoperative course was uneventful, with no complications. The patient was discharged on postoperative day 15, tolerating a full oral diet with normal bowel function. The 15-day length of stay primarily reflected the institutional postoperative pathway at the receiving hospital and the time required for final pathology review, multidisciplinary tumor board (MDT) discussion, and oncology consultation prior to discharge. Given high-risk features (stage IIIB, nodal metastases, lymphovascular invasion, poor differentiation, and mucinous histology), adjuvant CAPOX chemotherapy was initiated 1 month postoperatively after wound healing. He completed eight cycles with good tolerance and only mild toxicities (grade 1–2 hand-foot syndrome and transient thrombocytopenia).

Follow-up

At 7-month postoperative follow-up, he remained asymptomatic, with no radiologic evidence of recurrence or metastasis and normal CEA/CA19-9 levels. A summary timeline is provided in Table 1.

Table 1.

Timeline of clinical course and management

Time point (relative)	Key events and findings	Diagnostic work-up	Management / Outcome
Day −10 to Day 0	Intermittent colicky periumbilical/RLQ pain ×10 days; no fever/vomiting/hematochezia/weight loss	Vitals stable; mild RLQ tenderness without peritoneal signs; labs largely normal; hs-CRP 15.2 mg/L; PCT normal	Presented to ED; admitted
Day 0	Ileocecal intussusception (~7 cm), no obstruction/perforation/free fluid	Contrast-enhanced abdominal CT	Pneumatic enema reduction under fluoroscopy; successful; pain resolved
Day 1–2 (post-reduction)	Suspicious lead point detected in ascending colon (~4 cm)	Post-reduction US: heterogeneous solid lesion, irregular borders, increased vascularity; serum tumor markers (CEA/CA19-9/CA125/AFP) all normal	Proceeded to planned endoscopic evaluation
Day 3 (72 h after reduction)	Broad-based polypoid mass near the ileocecal valve (~4 cm), firm, ulcerated, with mucus adherent to the surface	Colonoscopy + multiple biopsies	Biopsy confirmed poorly differentiated mucinous adenocarcinoma with focal signet ring cell component
After biopsy (same episode)	MDT discussion; no distant metastasis on staging	Staging work-up including chest CT: no distant metastasis	Referred/transferred for definitive surgery (outside hospital)
Definitive surgery (outside hospital; 12 days after biopsy)	Localized right-sided colon tumor	—	Open right hemicolectomy with en bloc resection and regional lymph node dissection (ileocolic, right colic, middle colic basins)
Postoperative pathology	pT3; LVI present; 6/37 nodes positive (pN2a); margins negative; Stage IIIB; MMR proficient/MSS; Ki-67 ~50%; Trop2 strongly positive; Claudin18.2 positive	Histopathology + IHC	R0 resection
POD 15	Uneventful recovery	—	Discharged with full oral intake and normal bowel function
1 month after surgery	High-risk stage III features	—	Adjuvant CAPOX initiated; completed 8 cycles; mild grade 1–2 toxicities
7-month follow-up	Asymptomatic; tumor markers normal	Surveillance imaging: no recurrence/metastasis	Continue surveillance (q3 months ×2 years, then q6 months)

Abbreviations: AFP alpha-fetoprotein, CA125 cancer antigen 125, CA19-9 carbohydrate antigen 19-9, CAPOX capecitabine plus oxaliplatin, CEA carcinoembryonic antigen, CT computed tomography, ED emergency department, hs-CRP high-sensitivity C-reactive protein, IHC immunohistochemistry, LVI lymphovascular invasion, MDT multidisciplinary tumor board, MMR mismatch repair, MSS microsatellite-stable, PCT procalcitonin, pN2a pathological N2a stage, POD postoperative day, pT3 pathological T3 stage, RLQ right lower quadrant, US ultrasonography

Discussion

This case highlights a key diagnostic lesson: successful reduction of intussusception in an adolescent should not conclude the diagnostic evaluation. Unlike infantile intussusception, adolescent cases are uncommon and are more likely to be associated with an organic lead point. In our patient, CT established the presence of ileocecal intussusception but did not reveal the underlying lesion, which was subsequently detected by post-reduction ultrasonography and confirmed by colonoscopic biopsy. This sequence underscores a practical diagnostic approach in adolescents with atypical intussusception, particularly when the initial presentation is mild or nonspecific. It also emphasizes that normal serum tumor markers do not exclude malignancy and should not delay further investigation when imaging findings remain suspicious [3, 7].

From a literature perspective, this case lies at the intersection of two uncommon clinical settings: adolescent intussusception with a pathological lead point and intussusception secondary to colonic adenocarcinoma with mucinous features. In pediatric and adolescent reports, tumor-related lead points are more often lymphoid malignancies or other neoplastic lesions than primary colorectal adenocarcinoma [3, 8, 9]. By contrast, adult intussusception literature more commonly includes colonic adenocarcinoma, including mucinous histology, as a malignant lead point [10, 11]. Against this background, our case is particularly unusual because it combines adolescent age, ileocecal intussusception, and poorly differentiated mucinous adenocarcinoma with a focal signet ring cell component.

The pathological and therapeutic findings also add value to this report. The tumor showed retained expression of all four mismatch repair proteins, supporting proficient mismatch repair and microsatellite stability, and adjuvant CAPOX was administered on the basis of high-risk stage IIIB disease with reference to adult stage III colon cancer practice [4, 5, 12–14]. Although the prognostic and therapeutic significance of additional markers such as Trop2 and Claudin18.2 remains uncertain in pediatric colorectal cancer, documenting these findings may be informative in future recurrence management or molecularly guided treatment discussions. At the same time, interpretation should remain cautious because representative immunohistochemical microphotographs were unavailable from the outside institution, and long-term follow-up is still needed.

Conclusions

We report a rare case of poorly differentiated mucinous adenocarcinoma of the ascending colon, featuring focal signet ring cell morphology, which presented as ileocecal intussusception in a 15-year-old adolescent. This case highlights that successful reduction in adolescents should not end the diagnostic workup for a pathological lead point, and normal serum tumor markers should not provide false reassurance when imaging findings remain suspicious. Prompt tissue diagnosis and multidisciplinary oncologic management are important.

Patient perspective

Written informed consent for publication of this case report and accompanying images was obtained from the patient’s legal guardian. The patient and family expressed gratitude for the systematic evaluation that led to diagnosis and treatment of the underlying malignancy.

Reporting guideline

This case report is reported in accordance with the CARE guidelines; the completed CARE checklist is provided as Additional file 1.

Abbreviations

AFP

Alpha-fetoprotein

CA125

Cancer antigen 125

CA19-9

Carbohydrate antigen 19 − 9

CAPOX

Capecitabine plus oxaliplatin

CEA

Carcinoembryonic antigen

CT

Computed tomography

hs-CRP

High-sensitivity C-reactive protein

IHC

Immunohistochemistry

MDT

Multidisciplinary tumor board

MMR

Mismatch repair

MSS

Microsatellite stable

PCT

Procalcitonin

POD

Postoperative day

RLQ

Right lower quadrant

US

Ultrasonography

Authors’ contributions

JY and HL conceptualized and designed the study. HL and KZ contributed equally to this work and share first authorship. HL, KZ, and QG were involved in patient care, data collection, and analysis. HL and KZ drafted the initial manuscript. JY provided critical revision of the manuscript for important intellectual content. All authors read and approved the final manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

All relevant data are included in this published article. Any additional deidentified data are available from the corresponding authors upon reasonable request.

Declarations

Ethics approval and consent to participate

This case report was reviewed and approved by the Institutional Review Board of Wuhan Children’s Hospital (Tongji Medical College, Huazhong University of Science & Technology) (Approval No. 2024R049-E01). Written informed consent was obtained from the patient’s legal guardian.

Consent for publication

Written informed consent was obtained from the patient’s legal guardian for publication of this case report and any accompanying images.

Competing interests

The authors declare no competing interests.