Benign Mesenchymal Polyps with Focus on the Colon

...including the BUMP

General Remarks

• Usually asymptomatic lesions

• Incidental finding in (screening) coloscopy

• Usually solitary and small

Perineurioma

• Initially named ‚benign fibroblastic polyp‘

• Mucosa, sometimes involving submucosa

• Rectosigmoid colon

• Positive for perineurial markers

– EMA, GLUT-1 and claudin-1

• Negative for

– Vimentin, CK, SMA, Desmin, CD34, S100

Am J Surg Pathol 2010

Schwann Cell Hamartoma

• Initially called ‚mucosal neuroma‘

• ‚Schwannoma‘ and ‚Schwann Cell Hamartoma‘ considered synonymous according to WHO

• No association to genetic syndromes!

– i.e. NF1 and MEN2B

• S100 diffusely positive

S100

Ganglioneuroma

• Usually sporadic and solitary

– Syndromic association unlikely

• Located in mucosa

• Can occur in genetic polyposis syndrome

– MEN2B, NF1 and FAP

– Diffusely involves the bowel wall

• S100 diffusely positive

Granular Cell Tumor

• Mostly esophagus and right colon

– Colon: sumucosa, rarely extending into base of mucosa

– Esophagus: subepithelial, pseudoepithelial hyperplasia

• PAS positive, diastase resistant

• S100 positive (also inhibin and calretinin)

Leiomyoma

• Usually rectum and sigmoid colon

• Lamina muscularis mucosae

– esophagus: Tunica muscularis propria!

• Rarely symblastic

• Positive for SMA and desmin

• Negative for EMA, S100, CK and CD34

Finally...the BUMP

• Benign unclassified mesenchymal polyp

• ‚wastebasket‘

• ‘In our institution*, we diagnose these unnamed mesenchymal polyps simply as benign unclassified mucosal polyps or BUMPs’

*Department of Pathology, University of Michigan Hospital, Ann Arbor

‚Characteristics‘

• Spindled cells , adipocytes, blood vessels of all shapes and sizes

• Any type of stroma, including collagenous, elastic, and myxoid

• IHC specific for types of cells that make up their composition

Histopathology, 2015

• Benign Gastrointestinal Mesenchymal BUMPS Arch Pathol Lab Med. 2011;135:1311–1319

• Polypoid stromal lesions of the intestines Histopathology 2015, 66, 88–101

• Benign Serrated Colorectal Fibroblastic Polyps/Intramucosal Perineuriomas Are True Mixed Epithelial-stromal Polyps (Hybrid Hyperplastic Polyp/Mucosal Perineurioma) With Frequent BRAF Mutations

Am J Surg Pathol 2010;34:1663–1671

References