From Unexplained Iron-Deficiency Anaemia to Ileo-Ileal Intussusception: A Case Report of Primary Small Bowel Leiomyosarcoma

A man in his 60s presented to his general practitioner with intermittent abdominal pain, nausea, constipation, vomiting, and an unintentional weight loss of 6.4 kg over a 10-day period. Given these symptoms, his general practitioner arranged computed tomography of the abdomen and pelvis (CTAP). Three days after undergoing the CTAP, he presented to the emergency department with similar symptoms and was referred to the general surgery team. Table 1 summarises the timeline of the patient’s clinical presentation. On surgical assessment, he reported crampy abdominal pain on the background of a constant dull ache. He did not report any lower urinary tract symptoms. While he complained of constipation, he noted this was a common side effect of his iron supplementation. His relevant past medical history included IDA, which had been diagnosed years before this presentation. For this, he underwent repeated gastroscopies and colonoscopies, but no source for the anaemia was identified. His past surgical history consisted of a previous inguinal hernia repair. He had also been placed under active surveillance for prostate cancer. He reported an allergy to penicillin and had no history of smoking or alcohol use. His regular medications included mebeverine, ferrous sulphate, and laxatives. On physical examination, his abdomen was soft and non-tender, with no palpable masses or signs of peritonitis. There was no lymphadenopathy in the neck or in the groin. The CTAP demonstrated ileo-ileal intussusception without an obvious LP. A ‘target sign’ (Figure 1 ) and ‘bowel-within-bowel’ appearance (Figure 2 ), two characteristic signs of intussusception, were noted. There was mild upstream dilatation of the ileal loops (Figure 3 ) in the pelvis measuring approximately 4 cm in calibre. Faecal loading was noted in large bowel loops. There was no evidence of pneumoperitoneum or ascites. There were no clinical or radiological findings suggestive of bowel ischaemia. These CTAP findings confirmed the diagnosis of ileo-ileal intussusception. Laboratory investigations reported a normal leukocyte count, an elevated C-reactive protein level of 60 mg/L, and a low haemoglobin level of 107 g/L. Iron studies performed one month before this emergency department presentation reported a serum iron level of 4.70 µmol/L, a transferrin level of 2.06 g/L, and a transferrin saturation of 9%. His immediate supportive management included analgesia, intravenous fluids, ondansetron, prophylactic antibiotics (gentamicin and metronidazole), and venous thromboembolism prophylaxis (enoxaparin sodium). A nasogastric tube was inserted, and he was kept nil by mouth. Emergency surgery was planned because of the abdominal pain, CTAP findings of intussusception, and upstream small bowel dilatation consistent with small bowel obstruction. Under general anaesthesia, the patient was placed in a modified Lloyd-Davies position. An infra-umbilical 10 mm port was inserted using the modified Hasson’s technique and a pneumoperitoneum was created. Two 5 mm working ports were placed. An ileo-ileal intussusception was identified in the right hypochondrium (Figure 4 ) together with proximal small bowel dilatation. The intussusception was exteriorised through a midline laparotomy with a wound protector. After partial reduction, a small bowel stricturing lesion was noted along with multiple prominent mesenteric lymph nodes, the largest measuring 15 mm. Oncological resection of the involved small bowel and mesentery was performed with appropriate macroscopic margins. The mesentery was cut and ligated, and the bowel was stapled with a 100 mm linear cutter. Isoperistaltic side-to-side anastomosis was performed in two layers. The mesenteric defect was closed, the bowel was reduced into the abdomen, and the abdominal cavity was irrigated with sterile water. The peritoneum, rectus sheath, and skin were closed, and a dressing was applied. Postoperative care included intravenous fluids, enoxaparin sodium, catheter removal on postoperative day one, and appropriate mobilisation. He had an uneventful recovery and was discharged on postoperative day three. The resected specimen was a 17 cm segment of ileum with attached mesentery. Within the lumen, a polypoid, rubbery, whitish tumour with an ulcerated mucosal surface (4.0 × 4.0 × 2.5 cm) was present (Figure 5 ). The mass was situated on the mesenteric border of the bowel and served as the LP of the intussusception. It caused marked luminal narrowing and proximal bowel dilatation. The serosal surface showed focal retraction but not full-thickness perforation. The tumour was well-demarcated from surrounding tissues. It was located 10 cm from the proximal resection margin, 4 cm from the distal margin, and at least 5.5 cm from the nearest mesenteric margin. The remaining adjacent mucosa showed no abnormality and all resection margins appeared grossly uninvolved. Histological examination at low magnification revealed a malignant spindle cell neoplasm with an intersecting fascicular growth pattern within the bowel wall (Figures 6 , 7 ). The neoplastic cells showed abundant eosinophilic cytoplasm and elongated, blunt-ended hyperchromatic nuclei, exhibiting marked nuclear pleomorphism (Figures 6 , 7 ). High-power views highlighted cellular atypia and frequent mitotic figures, with an average of 15 per 10 high-power fields (Figure 8 ). No coagulative tumour necrosis was seen. The tumour invaded the submucosa and muscularis propria, but it did not penetrate the serosal surface. Mucosal ulceration was present. Lymphovascular invasion was not identified. Seven regional mesenteric lymph nodes showed reactive hyperplasia with no metastases. Both proximal and distal margins were free of tumour on microscopy. Immunohistochemistry confirmed smooth muscle differentiation of the neoplasm. The tumour cells showed diffuse strong positivity for smooth muscle actin (SMA) (Figure 9A ) and desmin (Figure 9B ). In contrast, no reactivity was seen for the epithelial marker AE1/3 (Figure 9C ) or neural marker S-100 protein (Figure 9D ). Importantly, markers associated with GIST were negative, with no expression of CD117/c-KIT (Figure 9E ) or CD34 (Figure 9F ). This immunoprofile supported smooth muscle differentiation and helped exclude a GIST or other mimics in this context. The Ki-67 labelling index of approximately 20% was seen in hot spots (Figure 10 ). The combination of gross morphology, histological features of spindle cell fascicles with cellular atypia, high mitotic activity, infiltrative growth limited to the bowel wall, and a smooth muscle immunophenotype supported the diagnosis of small bowel LMS. All resection margins were clear, and no lymph node metastases were identified. Computed tomography of the chest was performed 10 days postoperatively to assess for metastatic disease and was unremarkable, with no solid lung nodules or mass lesions identified. The patient was asymptomatic during his one-month follow-up clinic appointment. The case was further discussed at the sarcoma multidisciplinary team meeting. Another computed tomography of the chest, abdomen, and pelvis was performed on postoperative day 47, and there was no evidence of disease recurrence. At the two-month follow-up, his anaemia had resolved, his full blood count was within normal limits, and his haemoglobin level rose from 107 g/L before surgery to 133 g/L. He had received no perioperative blood transfusions. Iron studies showed a serum iron level of 9 µmol/L, a transferrin level of 2.7 g/L, and a transferrin saturation of 13%. These studies suggested mild residual iron deficiency, although a ferritin level was not available and the contribution of his iron supplementation could not be determined. Table 2 compares iron studies performed one month before surgery and two months after surgery. His liver function tests and renal function tests were also normal. The patient was advised to attend three-monthly follow-up appointments with repeat imaging. Reference ranges are based on the local clinical biochemistry user guide.

Intussusception refers to the telescoping of a gastrointestinal segment into an adjacent distal segment [ 1 ]. Adult intussusception is rare and is often associated with an underlying pathological lead point (LP). An LP is a lesion within the intestinal wall that is drawn distally by peristalsis along with the proximal bowel segment, resulting in intussusception. Neoplasms, either benign or malignant, account for 60% of identified LPs [ 2 ]. Ileo-ileal intussusception is a specific subtype of entero-enteric intussusception [ 3 ]. Clinical presentation in adults includes nonspecific symptoms such as abdominal pain, nausea, and vomiting [ 2 ]. If left untreated, intussusception can lead to necrosis, peritonitis, sepsis, and perforation [ 2 ]. Leiomyosarcoma (LMS) is a malignant soft-tissue neoplasm of smooth muscle differentiation that may arise in various organ systems, including the gastrointestinal tract. Small bowel LMSs are rare, accounting for approximately 0.1% to 3% of small bowel malignancies [ 4 ]. Patients with small bowel LMS may present with chronic abdominal pain, weight loss, and gastrointestinal bleeding [ 4 ]. We report the case of a man in his 60s with long-standing unexplained iron-deficiency anaemia (IDA) who underwent multiple upper and lower gastrointestinal endoscopic investigations, but the source of the anaemia could not be identified. Years after the initial diagnosis of IDA, he presented with ileo-ileal intussusception secondary to a primary small bowel LMS. The combination of histology and immunohistochemistry helped distinguish the LMS from a gastrointestinal stromal tumour (GIST). The intraluminal tumour showed mucosal ulceration, providing a plausible source of chronic occult gastrointestinal blood loss. It subsequently served as the LP for intussusception. This case adds to the limited literature on small bowel LMS presenting with ileo-ileal intussusception and highlights the combination of long-standing unexplained IDA, unrevealing conventional endoscopic investigations and subsequent presentation with ileo-ileal intussusception requiring emergency surgery. This case was previously presented as e-posters at the 8th Annual East Kent Surgical Conference on November 14, 2025 and the Association of Surgeons of Great Britain and Ireland International Surgical Congress 2026 on May 13, 2026. It was also presented as a short oral presentation at the 8th Nepalese Doctors Association UK Resident Doctors Conference on June 6, 2026.

Adult intussusception accounts for approximately 5% of all intussusception cases, with the majority occurring in the paediatric population. It represents 1% of all small bowel obstructions and is reported in fewer than 1 in 1,300 abdominal operations [ 2 ]. In contrast to paediatric patients, adult cases often have an underlying pathological LP. Neoplasms, either benign or malignant, account for 60% of identified LPs [ 2 ]. Other non-neoplastic, non-idiopathic causes include postoperative adherences, coeliac disease, Crohn’s disease, endometriosis, and infections [ 2 ]. Based on anatomical location, intussusception can be classified into the following four categories: (i) entero-enteric (involves the small bowel only), (ii) ileo-cecal (the ileocecal valve serves as the LP for intussusception), (iii) ileo-colic (the terminal ileum telescopes into the ascending colon), and (iv) colo-colic (involves the large bowel only) [ 3 , 5 ]. Ileo-ileal intussusception is a specific subtype within the entero-enteric category [ 3 ]. Adult intussusception may present with abdominal pain, nausea, vomiting, and a palpable abdominal mass on physical examination [ 1 , 2 ]. Other associated symptoms such as weight loss may indicate the presence of an underlying serious pathology, including a malignant LP [ 6 ]. If left untreated, necrosis, peritonitis, sepsis, and perforation may occur [ 2 ]. Computed tomography is the imaging modality of choice for diagnosing adult intussusception. Typical computed tomography findings include the ‘target’ or ‘sausage’ sign and ‘bowel-within-bowel’ appearance [ 1 ]. Surgery is the recommended, definitive treatment for adult intussusception [ 1 ]. The surgery can be performed with or without a primary reduction, although reduction before resection may allow a more limited bowel resection [ 1 ]. However, the risks of reduction before resection include intraluminal seeding and venous embolisation of malignant cells in the region of the ulcerated mucosa, bowel perforation, and anastomotic complications when the bowel is oedematous and inflamed [ 1 ]. LMS is a malignant soft-tissue neoplasm of smooth muscle differentiation that may arise in various organ systems, including the bladder, gastrointestinal tract, uterus, or blood vessels. Small bowel malignancies account for approximately 2% of all gastrointestinal malignancies [ 4 ]. A population-based study showed that adenocarcinomas accounted for 38% of all small bowel malignancies, followed by neuroendocrine tumours (35%), lymphomas (15%), and sarcomas (12%) [ 7 ]. Small bowel LMS is a subtype of sarcoma, accounting for approximately 0.1% to 3% of small bowel malignancies [ 4 ]. Patients with small bowel LMS may present with chronic abdominal pain, weight loss, gastrointestinal bleeding, and anaemia [ 4 ]. Diagnosing small bowel LMS involves imaging techniques, histopathology, and immunohistochemistry. On computed tomography, these cancers are heterogeneous, show low central attenuation due to necrosis, and may show calcification, although this is exceedingly rare [ 8 ]. On magnetic resonance imaging, these tumours often demonstrate cystic foci, with signal intensity varying according to the imaging sequence [ 8 ]. On T1-weighted imaging, they are isointense to muscle, while on T2-weighted imaging, they are intermediate to hypointense relative to neighbouring fat tissue [ 8 ]. On gross pathology, they appear as white-grey masses and, when large, they may be associated with haemorrhage, necrosis, and cystic changes [ 9 ]. Microscopically, they display long intersecting fascicles of spindle-shaped cells with nuclear pleomorphism [ 9 ]. LMS may histologically resemble GIST, as both may present as spindle cell malignant neoplasms with high mitotic counts, necrosis, and cytological atypia. Immunohistochemistry is essential to differentiate these tumours. In small bowel LMS, positive staining for smooth muscle markers such as SMA and desmin supports the diagnosis, while negative staining for CD117 helps distinguish it from GIST [ 9 ]. In our patient, the tumour matched the macroscopic, microscopic, and immunohistochemical features of a typical small bowel LMS. Treatment of small bowel LMS primarily involves complete surgical resection of the tumour with negative margins [ 4 ]. Similar cases of small bowel LMS causing intussusception have previously been reported [ 10 - 13 ]. Table 3 compares this case with previously reported cases. Štor et al. [ 10 ] reported that before admission, their patient had undergone oesophagogastroduodenoscopy and colonoscopy due to abdominal pain and anaemia. These demonstrated erosive gastritis and sigmoid colon diverticulosis, respectively, which may have provided alternative explanations for the anaemia. Rayasam et al. [ 13 ] also reported that upper gastrointestinal endoscopy performed one month before surgery was normal. In contrast, the repeated upper and lower endoscopic investigations in our patient were unremarkable and failed to identify a source for the IDA. At the two-month follow-up after resection of the LMS, the anaemia resolved, although iron studies showed mild residual iron deficiency. The histological finding of tumour-associated mucosal ulceration provides a plausible source for chronic occult gastrointestinal blood loss that may have contributed to the patient’s long-standing unexplained IDA. Among the other published cases reviewed, similar repeated gastrointestinal investigations to identify the source of IDA before presentation were not described.

Adult intussusception requires early recognition because the presentation is often nonspecific, and delayed management can lead to severe complications such as bowel ischaemia, necrosis, and perforation. It is also important to consider an underlying malignant LP, especially when associated features such as unintentional weight loss and IDA are present. In this case, tumour-associated mucosal ulceration provided a plausible source of chronic occult gastrointestinal blood loss that may have contributed to the patient’s long-standing unexplained IDA. This case highlights small bowel LMS as a rare malignant LP for ileo-ileal intussusception. Timely imaging and prompt surgical intervention enabled definitive treatment. Immunohistochemistry was vital in confirming the diagnosis of small bowel LMS and excluding histological mimics, particularly GIST. Continued surveillance and multidisciplinary follow-up are important to monitor for disease recurrence or metastatic disease.