Filiform Polyposis of the Terminal Ileum as the Initial Manifestation of Crohn’s Disease: A Case Report

Introduction

Filiform polyposis (FP) is a rare subtype of inflammatory pseudopolyp, characterized by elongated, finger-like mucosal projections [1]. It most frequently occurs secondary to IBD, particularly ulcerative colitis, and is typically found in the colon and rectum [2], with all reported cases so far being confined to the colon. Its pathogenesis remains unclear but is often attributed to chronic cycles of mucosal ulceration and healing [2]. This report presents a unique case in which FP in the terminal ileum was the initial manifestation of CD, a scenario not previously documented in the literature.

Case Report

A 52-year-old woman reported having loose stool for 1 month in November 2022, without other gastrointestinal symptoms. Her history included breast cancer treated with toremifene, concluded in 2021. She had no family history for IBD or medical history of any digestive system disease. Subsequently, she underwent a colonoscopy at a local medical facility, which found a bulging mass in the terminal ileum, colitis, and hemorrhoids, which lead her to come to our hospital for surgical treatment. Initial investigations revealed anemia (hemoglobin 85 g/L), elevated inflammatory markers (CRP 18 mg/L, ESR 86 mm/H), and a positive fecal occult blood test. She had negative results from tumor markers, serum protein electrophoresis, hepatitis virus, stool smear, stool culture, quantitative EBV, quantitative cytomegalovirus, syphilis binomial, HIV antibody, T-SPOT.TB, PPD, renal function, blood glucose, antinuclear antibody, anti-double-stranded DNA antibody, ANCA binomial, HLA-B27, and TPMT gene test.

Colonoscopy identified a large, branched mucosal bulge with congestion and edema in the terminal ileum (Figure 1) and diffuse basal cell carcinomas or aphthous ulcers throughout the colorectum (Figure 2), with normal-appearing mucosa between the lesions, suggesting CD and an undetermined ileal mass. Endoscopic ultrasonography characterized the ileal mass as a moderately echogenic lesion within the lamina propria, measuring 12.32×19.07 mm (Figure 3). Computed tomography enterography (CTE) confirmed inflammatory involvement of the terminal ileum and right colon (Figure 4). Histopathology revealed chronic active inflammation with patchy inflammatory infiltrates (Figure 5). Magnetic resonance imaging (MRI) with and without contrast showed no significant abnormalities in the anal canal, but an osteitis condensans ilii was detected.

A preliminary diagnosis of CD was made, and the patient was initially treated with mesalazine, Compound Glutamine Enteric-coated Capsules, traditional Chinese medicine Shen Ling Bai Zhu San, and supportive care. While symptoms improved, follow-up colonoscopy at 3 months showed persistent ileal mass and ulcers. Pathological biopsy indicated a chronic active inflammation in the mucosa of the terminal ileum and cecum, while the mucosa of the ascending and transverse colon exhibited chronic inflammatory changes, but the mucosa of the descending colon, sigmoid colon, and rectum did not show any overt lesions. The biopsy of the terminal ileal mass was microscopically characterized as inflammatory granulomatous tissue (Figure 6). CTE indicated irregular soft tissue in the terminal ileum, similar to the prior findings, but with reduced inflammation. A multidisciplinary consultation with the IBD Center of Sir Run Run Shaw Hospital, Zhejiang University was held, and the ileal lesion was considered most consistent with filiform polyp secondary to underlying CD. A prioritizing treatment of the intestinal inflammation was recommended. Given her history of breast cancer, Ustekinumab was selected as the preferred biologic therapy.

After 3 courses of Ustekinumab, the symptoms resolved and inflammatory markers normalized. CTE indicated reduced intestinal inflammation. Follow-up colonoscopy showed complete resolution of the intestinal ulcers. The FP mass was then successfully resected using hybrid endoscopic submucosal dissection (Figure 7). Final pathology confirmed the diagnosis of a filiform polyp (Figure 8). To date, the patient remains in remission with no recurrence.

Discussion

Filiform polyp (FP) is a specific subtype of inflammatory pseudopolyp named for its characteristic elongated, finger-like projections. This condition, often presenting as multiple lesions, is termed filiform polyposis [1]. This case is remarkable for several reasons. First, FP occurring in the terminal ileum is highly unusual, as it typically manifests in the colon [3]. Second, although FP as a presenting feature of IBD has been documented [4], its occurrence as the index lesion for CD – particularly in the uncommon location of the terminal ileum – is a rare and noteworthy presentation. Typically, FP is a sequela of long-standing, quiescent IBD. The patient’s lack of typical CD’s symptoms (eg, abdominal pain, weight loss) and only mildly active inflammation may have allowed an extended period of mucosal injury and repair, facilitating the development of this large FP.

Gross characteristics of FP include sessile or pedunculated lesions, with some 2~3 cm or even longer. Morphologically, they present as multiple mucosal protrusions, or elongated columnar projections that can bridge together or form conglomerate masses. Endoscopically, these appear as numerous worm-like, labyrinthine, or villous polyps, macroscopically resembling villous adenomas [5]. When the colon is diffusely involved, endoscopic findings can mimic familial adenomatous polyposis (FAP). Some polyps develop a mushroom-cap morphology, leading to potential misclassification as malignant lesions on endoscopy or imaging studies. The microscopic features of FP are characterized by normal intestinal mucosal epithelium covering a lamina propria rich in inflammatory cells and distorted crypts, with evident crypt dilation, branching, and hyperplasia, occasionally accompanied by crypt abscesses, surface erosions, and varying amounts of granulation tissue [6].

The pathogenesis of FP remains unclear. It most frequently occurs secondary to IBD. It is postulated that chronic mucosal inflammation with recurrent ulceration and healing in the large intestine lead to formation of finger-like polypoid projections [7]. Some researchers have observed disorganized proliferation of fibrovascular and neuromuscular components in case studies, leading to the hypothesis that the pathogenesis of filiform polyps can resemble a hamartomatous process [8]. Other scholars propose that locally produced inflammatory cytokines and growth factors in the mucosa can drive polyp formation [3]. Recent Chinese and international reports [9,10] indicate that most cases are benign, with rare occurrences of adenomatous changes or malignant transformation. Although FP themselves have a low carcinogenic potential, surveillance for dysplasia in the surrounding mucosa remains essential for patients with IBD.

Our patient was hospitalized primarily due to FP. Apart from loose stools, no typical clinical manifestations of CD were observed. Ancillary tests indicated mild inflammatory activity, suggesting that these factors provided an extended time window for the development of large-volume FP. Unlike previously reported predilection sites for FP, this case demonstrated FP formation in the terminal ileum, a region characteristically affected in CD. This anatomical correlation points to recurrent mucosal injury at this site as the likely instigator of FP development. Compared to common inflammatory polyps of the intestine, this case of FP presented a rare macroscopic appearance as a multi-branching conglomerate mass. Microscopically, it exhibited marked mucosal hyperplasia with arborizing or broad villiform surfaces and distorted, branched crypts. Furthermore, the stroma demonstrated dense fibrovascular proliferation and intense acute/chronic inflammatory infiltrates, accompanied by ulceration and granulation tissue formation. These distinct characteristics underscore the unique histopathological signature of FP that differentiates it from other inflammatory polyps. FP is rare, documented in only 10% to 20% of IBD cohorts despite systematic endoscopic surveillance [11]. While FP is recognized as a sequela of medically managed IBD [11–14], particularly in quiescent ulcerative colitis, its presentation as the index manifestation prompting de novo IBD diagnosis remains unreported in the literature to date.

This case underscores that FP can be the “tip of the iceberg”, masking underlying chronic IBD. It highlights the critical importance of a multidisciplinary approach to thoroughly investigate the etiology of such lesions, rather than focusing solely on their removal. Key questions remain regarding whether Crohn’s patients presenting with FP have distinct genetic phenotypes or disease courses, warranting large-scale cohort studies.

Conclusions

This report describes a novel presentation of filiform polyposis as the initial manifestation of CD in the terminal ileum. It illustrates that the discovery of FP should prompt a comprehensive evaluation for underlying IBD, even in the absence of classic clinical symptoms. Multidisciplinary collaboration is essential for accurate diagnosis and optimizing management, which may involve biologic therapy to control the underlying inflammation before addressing the polyp itself. This case expands the clinical spectrum of FP and emphasizes its role as an indicator of occult intestinal inflammation.