Reactive nodular fibrous pseudotumor involving the gastrointestinal tract and mesentery: A case report and review of the literature

Abstract

Reactive nodular fibrous pseudotumor (RNFP) is a tumor-like lesion that is characterized by reactive fibroblast/myofibroblast proliferation within collagenic hyalinized stroma, due to its association with injury or inflammation. The current study describes the case of a 60-year-old female with a history of abdominal surgery and abdominal pain. Upon laparoscopy, multiple nodules attached to the outer layer of the colon and mesentery were identified, and therefore, complete surgical excision was performed. Macroscopically, the nodules were well-circumscribed, firm, tan-white in color and ranged in size between 2.0-10.0 cm at the greatest dimension. Microscopically, the nodules were composed of spindle and stellate cells in a dense collagenic hyalinized background with sparse lymphocytic infiltration. Immunohistochemical analysis demonstrated positive staining for vimentin, smooth muscle actin and cluster of differentiation (CD) 117, and focally-positive keratin staining with AE1/AE3; however, no staining was observed for gastrointestinal stromal tumor 1, CD34, S-100, anaplastic lymphoma kinase or β-catenin. Therefore, it was proposed that the lesion may be most accurately described as an RNFP. The current study reports a rare case of RNFP, emphasizing its histopathological features and differential diagnoses to promote an improved and broader understanding of this poorly understood condition.

Keywords: differential diagnosis; gastrointestinal tract; mesentery; reactive nodular fibrous pseudotumor.

Figure 1

(A) Macroscopic image of the surgical specimen demonstrating multiple tan-white nodules (arrows) of varying sizes attached to outer layer wall of the colon and mesentery. (B) Reactive nodular fibrous pseudotumor (RNFP) of the colon infiltrating and replacing the muscularis propria and encroaching on the submucosa (magnification, ×100). (C) RNFP were composed of proliferative spindle and stellate cells resembling fibroblasts/myofibroblasts in a dense collagenic hyalinized background (magnification, ×400), with (D) specific RNFP nodules containing a more cellular peripheral zone composed of active fibroblasts. (magnification, ×200). (E) Diffuse strong immunohistochemical staining for smooth muscle actin (magnification, ×400) and (F) focal AE1/AE3 expression, particularly in the peripheral cellular zone (magnification, ×200; hemaoxylin and eosin staining).