A Comparative Analysis of GISTs and Schwannomas in the Sigmoid Colon: Case Report and Review of the Management Strategies

Abstract

Background/Objectives: Mesenchymal tumors of the gastrointestinal tract are rare and can pose significant diagnostic challenges, particularly when located in atypical sites such as the sigmoid colon. Gastrointestinal stromal tumors (GISTs) are often the primary consideration based on imaging findings; however, other spindle cell neoplasms, such as schwannomas, must also be considered. We present a case of a sigmoid colon schwannoma initially suspected to be a GIST and provide a literature review on the diagnostic and therapeutic challenges associated with these tumors. Methods: A literature review based on articles from 2015 to 2024 was conducted to identify cases of mesenchymal tumors of the colon misdiagnosed as GISTs. The review focused on the role of imaging, endoscopic biopsy, and immunohistochemistry in differentiating these neoplasms. Additionally, treatment approaches, including surgical resection versus targeted therapy, were assessed. Results: The literature review revealed that GISTs and schwannomas share overlapping imaging characteristics, including submucosal location, hyperintensity on T2-weighted MRI, and contrast enhancement. However, immunohistochemical markers remain the gold standard for differentiation. Studies also highlighted the increasing role of minimally invasive diagnostic techniques, such as fine-needle aspiration and molecular profiling, in achieving a definitive preoperative diagnosis. Unlike GISTs, which often require adjuvant therapy with tyrosine kinase inhibitors, schwannomas are typically treated with surgical excision alone, with a low risk of recurrence. Conclusions: Current evidence supports a multimodal diagnostic approach combining imaging, biopsy, and immunohistochemistry to accurately classify mesenchymal tumors of the colon. While imaging can suggest a probable diagnosis, histopathological confirmation is essential before initiating targeted therapy.

Keywords: colorectal tumors; gastrointestinal stromal tumor; immunohistochemistry; mesenchymal tumors; schwannoma.

Figure 1

(a) Coronal fused PET/CT image demonstrating metabolic activity throughout the body. Physiological uptake is observed in the brain, kidneys, and bladder. A focal area of increased FDG uptake is identified in the lower abdomen, corresponding to the sigmoid colon (arrow), consistent with a metabolically active lesion; (b) Coronal contrast-enhanced CT scan of the thoracoabdominal region. The sigmoid colon is visible in the lower abdomen, with no obvious signs of obstruction or perforation. No lymphadenopathy or distant organ lesions are noted.

Figure 2

(a) Coronal post-contrast T1-weighted MRI showing a 20 mm enhancing submucosal lesion in the sigmoid colon (arrow), with well-defined margins and no adjacent invasion; (b) Coronal T2-weighted pelvic MRI showing a well-defined submucosal lesion in the anterior sigmoid colon wall (arrow), measuring approximately 17–22 mm, with intermediate-to-high signal intensity and no signs of adjacent invasion.

Figure 3

Endoscopic ultrasound (EUS) showing a well-defined, hypoechoic, vascularized submucosal lesion (20 × 16 mm) arising from the muscularis propria of the sigmoid colon (arrows).

Figure 4

The resected specimens were fixed with 10% formalin fixative and 95% ethanol fixative, dehydrated, embedded in wax, sectioned, and stained with hematoxylin and eosin (Tissue-Tek Prisma). (a) 40×—Schwannoma, overview. Low-power view shows a well-circumscribed submucosal lesion beneath the colonic mucosa, composed of intersecting bundles of spindle-shaped cells exhibiting a storiform arrangement. The overlying mucosa is intact, and there is no evidence of ulceration or invasion into adjacent layers. The lesion demonstrates a fascicular architecture, characteristic of a mesenchymal neoplasm such as schwannoma; (b) 200×—Schwannoma, cellular morphology. At higher magnification, the lesion is composed of spindle cells with elongated, wavy nuclei arranged in interlacing fascicles. Nuclear palisading is focally observed, along with areas of collagen deposition between the cellular bundles.

Figure 5

Positive Immunohistochemical Markers Supporting Schwannian Differentiation (S100, GFAP). (a) S100, 400×—Schwannoma, strong immunoreactivity. High-power view showing diffuse and intense nuclear and cytoplasmic positivity for S100 protein in the spindle cells. This strong, uniform staining pattern is highly characteristic of schwannoma, confirming the neural crest origin of the tumor cells. S100 is considered the most sensitive and specific immunohistochemical marker for schwannomas.; (b) GFAP, 200×—Schwannoma, positive immunostaining. Intermediate magnification image demonstrating cytoplasmic positivity for GFAP (glial fibrillary acidic protein) in spindle cells. GFAP expression further supports the glial/neuroectodermal differentiation of the lesion. While not as specific as S100, it provides additional evidence for diagnosis of schwannoma.