S3818 Rare Case of Granular Cell Tumor of the Anal Region

Introduction: Granular cell tumors (GCTs) are uncommon, typically benign neoplasms thought to originate from Schwann cells of peripheral nerve sheaths. These tumors can arise in various locations, most frequently involving the skin, tongue, and gastrointestinal tract. Anal or perianal GCTs are exceptionally rare, with fewer than 4 cases reported in the literature. Histologically, GCTs are composed of large polygonal cells with eosinophilic granular cytoplasm, representing lysosomes in different stages of degradation. Immunohistochemical staining is typically positive for S-100 and SOX-10 supporting their neural origin. Clinically, GCTs are often asymptomatic and found incidentally. When symptomatic, the presentation is usually related to tumor size and location, with symptoms including pain, pruritus, bleeding, or palpable mass. Malignant transformation is rare, occurring in 1%–2% of cases. Case Description/Methods: We report the case of a 50-year-old man who presented with an 8-week history of perianal pain, bleeding on wiping, and pruritus. He had no significant past medical or family history. On examination, a firm, non-tender, submucosal lesion measuring approximately 5 cm was palpated at the 4 o’clock position in the anal canal. There were no signs of infection or abscess. Digital rectal examination and anoscopy confirmed a well-defined lesion abutting the anal sphincter however contrast enhanced magnetic resonance imaging of the pelvis revealed a 5 cm well defined ovoid lesion approximately 1 cm above the anal verge without any evidence of anal sphincter invasion. The patient underwent transanal surgical excision under general anesthesia. Gross examination showed a well-defined mass excised en bloc with clear margins. Histopathological analysis revealed features typical of GCT. Immunohistochemistry confirmed the diagnosis with positive staining for S-100 and SOX-10. Although the tumor abutted the closest medial margin, no features of malignancy were present, and the Ki-67 index was low. Postoperatively, the patient recovered well and remained asymptomatic at 4 months follow-up, with no recurrence. Discussion: This case underscores the importance of including GCT in the differential diagnosis of anal masses. Magnetic resonance imaging aids in preoperative assessment, and histopathology with immunohistochemistry remains the gold standard for diagnosis. Complete surgical excision remains the treatment of choice, and long-term follow-up is recommended due to the risk of recurrence or rare malignant transformation.