Pseudo-Pseudo Polyp: Spindle Cell Sarcoma at an Ileocolonic Anastomosis

ABSTRACT

Anastomotic inflammatory polyps are a known source of gastrointestinal bleeding in patients who have undergone bowel resection, but an anastomotic spindle cell sarcoma with myogenic differentiation has never been reported. We present the case of a patient with occult gastrointestinal bleeding 6 years after an ileocolic resection for an incarcerated hernia and discuss surveillance in patients with these rare polyps.

INTRODUCTION

Inflammatory polyps are characteristically sessile, hypopigmented polyps near healed or partially healed sites of inflammatory, ischemic, or infectious bowel injury. These can also occur postoperatively due to traction or retained suture at a mucosal anastomosis. Intervention is required if patients develop refractory anemia or signs of bowel obstruction related to the polyp. In this case, an anastomotic polyp causing symptomatic anemia was on pathology revealed to be a spindle cell sarcoma with myogenic differentiation, suspicious for myxoid leiomyosarcoma. Soft tissue sarcomas are rare tumors, representing 1%–2% of all adult cancers.¹ Gastrointestinal leiomyosarcomas account for less than 0.1% of all colorectal malignancies, and myxoid leiomyosarcomas are even more rare, with no previous colonic cases reported.² The goal of this case report was to better understand the prognosis and surveillance of poorly differentiated colonic sarcomas.

CASE REPORT

A 58-year-old woman with a complex surgical history was admitted to the hospital for symptomatic anemia without overt bleeding. Six years before, she underwent a hysterectomy for benign fibroids, which was complicated by an incarcerated incisional hernia with perforation, requiring an ileocolic resection of 1.5 feet. Pathology from the ileocolic resection showed reactive changes, acute and chronic serositis, and mild acute enteritis at the ileal margins. A postoperative colonoscopy 5 years later showed only internal and external hemorrhoids, with a normal-appearing ileocolic anastomosis. She had no family history of gastrointestinal malignancy or inflammatory bowel disease.

At initial evaluation, her hemoglobin had dropped from 12.5 to 6.8 g/dL over the past year. Laboratory studies also showed a transferrin saturation of 5% and a ferritin of 11 ng/mL. She reported sporadic ibuprofen use and took daily aspirin. An inpatient upper endoscopy and colonoscopy were performed to identify the source of her profound iron deficiency anemia. Upper endoscopy was unremarkable, but colonoscopy revealed a white, nodular, semipedunculated 35 mm polyp with a pigmented spot at the end-to-side ileocolic anastomosis (Figure 1). Presuming this polyp was inflammatory in nature and the source of her bleeding, we removed it with hot snare. The patient was discharged the day following the procedure.

Figure 1.

Colonoscopy findings. (A) Semipedunculated polyp seen at ileocolic anastomosis. (B) Pigmented spot seen on same semipedunculated polyp.

Unexpectedly, pathology revealed the polyp to be a spindle cell neoplasm with myogenic differentiation, exhibiting brisk mitotic activity, a Ki-67 nuclear proliferation rate of up to 30%, peripheral ulceration, and secondary necrosis at the margin. Specialized staining confirmed a final diagnosis of spindle cell sarcoma with myogenic differentiation, suspicious for grade 2 myxoid leiomyosarcoma by the Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) criteria (Figure 2). Metastasis from a uterine primary was excluded by reviewing the pathology slides from her prior hysterectomy. Computerized tomography (CT) scans of the chest, abdomen, and pelvis revealed no distant metastasis, and she underwent secondary ileocolic resection. The pathology of the resected bowel showed mildly active chronic enteritis, foreign body reaction around suture material, and no residual tumor, including in 0/7 lymph nodes. Thus, the tumor was pathologically staged as T1N0M0. At follow-up, our patient felt well with no recurrence of anemia. Given her low-moderate grade and lack of metastatic disease, we elected to repeat cross-sectional imaging at 6 months after her initial resection. Follow-up CT scan is ordered.

Figure 2.

Pathology slides of the tumor. (A) Slide of the polyp. (B and C) Spindle cells arranged in long fascicles. Black arrow area of myxoid changes. (D) Eosinophilic cytoplasm and ovoid nuclei, typical of spindle cells.

DISCUSSION

Inflammatory polyps occur in 14.5% of patients within 7 years after colonic resection for colorectal cancer.³ The inflammatory nidus may relate to retained suture, traction, and mucosal twisting during peristaltic waves, causing localized ischemia and fibrosis. These polyps should be removed if patients have symptoms, such as bowel obstruction or profound anemia, as in our patient's case.

Surprisingly, this nodular white polyp turned out to be an extremely rare, malignant polyp, requiring multiple specialized stains to obtain the final diagnosis. Gastrointestinal stromal tumor was excluded with negative Cluster of Differentiation 117, Cluster of Differentiation 34, and Discovered On GIST-1 staining.⁴ Schwannoma was excluded with S100 negativity.⁵ Smooth Muscle Actin and Desmin were positive, suspicious for a diagnosis of leiomyosarcoma.⁴ Spindle cell rhabdomyosarcoma was excluded with negative Myogenin and Myogenic Differentiation Antigen 1, and kinase fusion-positive inflammatory myofibroblastic tumor was excluded with negative pan Neurotrophic Tyrosine Receptor Kinase and Archer Fusion Plex (Table 1). The final diagnosis was a spindle cell sarcoma with myogenic differentiation, suspicious for myxoid leiomyosarcoma.

Table 1.

Immunostains and the corresponding tumors they identify

Immunostains		Result
CD117	Gastrointestinal stromal tumor	Negative
CD34		Negative
DOG 1.1		Negative
S100	Schwannoma	Negative
SMA	Leiomyosarcoma	Positive
Desmin		Positive
Myogenin	Spindle cell rhabdomyosarcoma	Negative
MyoD1		Negative
panNTRK	Kinase fusion-positive inflammatory myofibroblastic tumor	Negative
Archer fusion plex		Negative

CD, cluster of differentiation; DOG1.1, Discovered On GIST-1; MyoD1, Myogenic Differentiation Antigen 1; panNTRK, pan Neurotrophic Tyrosine Receptor Kinase; SMA, smooth muscle actin.

Given the patient's history of hysterectomy and pathology findings, the initial concern was that this neoplasm originated from the uterus. However, a review of prior hysterectomy slides showed no evidence of sarcoma. A more likely mechanism for the development of this tumor is chronic inflammation at the anastomotic site, leading to uncontrolled spindle cell proliferation during chronic tissue regeneration.⁶

This is the first documented case of colonic spindle cell sarcoma with myogenic differentiation. Given its rarity, we faced considerable uncertainty regarding appropriate surveillance. We can only extrapolate from the existing literature on this rare entity, which has compared the clinical courses of nongynecologic leiomyosarcomas and sarcomas with myogenic differentiation (SMD), the natural history of which may be driven by the grade of tumor, regardless of initial site. Notably, 14% of patients with low-grade tumors had no recurrence or progression at 8 years. In medium-to-high grade tumors, the 8-year incidence of distant metastasis was 39% for patients with leiomyosarcoma and 33% for patients with SMD. The estimated 8-year overall survival for patients with grade 2 or 3 tumors classified as leiomyosarcomas 67% and 64% for SMD.⁷

Extragastrointestinal leiomyosarcomas and SMD have an overall high rate of metastasis, even after resection.^7–9 Myxoid variants behave more aggressively.^9,10 European guidelines for soft tissue and visceral sarcomas suggest that patients with tumors with intermediate to high histologic grade should have cross-sectional imaging 4 times a year in the first 2 years; twice a year until year 5, and annually thereafter. Patients with low-grade tumors may be followed twice a year in the first 5 years, then annually thereafter.^11,12 Adjuvant chemotherapy is recommended for uterine leiomyosarcoma and can be used for colonic leiomyosarcoma.^13–15 However, the overall survival benefit is unclear, and the National Comprehensive Cancer Network recommends individualized treatment of retroperitoneal and intrabdominal sarcomas.^2,16–18 To conclude, this colonic spindle cell sarcoma with myogenic differentiation is a rare neoplasm with uncertain course, requiring close surveillance.

DISCLOSURES

Author contributions: I. Varela Knorr and J. Claytor conducted the background research and prepared the initial draft of the manuscript. All authors contributed to the revision of earlier drafts and reviewed and approved the final version of the manuscript. J. Claytor is the article guarantor.

Financial disclosure: None to report.

Previous presentation: This case report has been presented during the DDW conference; May 21, 2024; Washington, District of Columbia.

Informed consent was obtained for this case report.