Sessile serrated adenoma

Sessile serrated adenoma, abbreviated SSA, is a premalignant polyp of the large bowel.

Sessile serrated adenoma
Diagnosis in short
SSA. H&E stain.
Synonyms	sessile serrated lesion, sessile serrated polyp, sessile serrated adenoma/polyp
LM	serrated epithelium, crypt base dilation, crypt branching, boot-shaped glands, horizontal glands
LM DDx	hyperplastic polyp, tubular adenoma (when with dysplasia)
Site	colon - usually cecum or ascending colon
Associated Dx	colorectal adenocarcinoma, hyperplastic polyp
Syndromes	serrated polyposis syndrome, MUTYH polyposis syndrome
Prevalence	common
Endoscopy	flat, usually > 5 mm, mucinous cap
Clin. DDx	normal, hyperplastic polyp, other intestinal polyps

It is also known as sessile serrated polyp (abbreviated SSP), sessile serrated lesion and sessile serrated adenoma/polyp (abbreviated SSA/P).

This lesion should not be confused with the traditional serrated adenoma, previously known as serrated adenoma.

General

• Colonic lesion.
• May be seen in the context of serrated polyposis syndrome.

Epidemiology:

• Thought to lead to colorectal cancer through a different pathway than most tumours in the left colon/rectum.
• Microvesicular hyperplastic polyps are hypothesized to be the the precursor of SSAs.

Gross

Features:

• Flat lesions, usually > 5 mm.
• Typically have a "mucous cap" - present ~65% of the time; useful for identification.
• Border not well-demarcated.
• More common in the proximal colon.

Note:

• Sessile lesions over 1 cm are usually SSAs.

Image:

• SSA - endoscopy (nature.com).

Microscopic

Features:

• Serrated epithelium at the surface and deep in the crypts.
  • Saw-tooth appearance, epithelium has jagged appearing edge.
• Crypt dilation at base with serrations - key feature.
  • Very common -- anecdotally the most sensitive feature.
• "Boot"-shape or "L"-shaped glands.
  • Shape may be similar to a hockey stick.
• Horizontal crypts = crypt long axis parallel to the muscularis mucosae.
• Crypt branching.

Minimal extent criteria - number of abnormal crypts with the above features:

• German Society of Pathology proposal: at least two abnormal crypts -- crypts do not have to be adjacent.
• An expert panel lead by Rex states that one unequivocally altered crypt should prompt calling SSA.
• The WHO requires - depending on what you read:
  • Three adjacent crypts to be abnormal.
  • Two or three adjacent crypts to be abnormal.

Notes:

• Typically do not have nuclear atypia, i.e. no nuclear crowding, no nuclear hyperchromasia, no cigar-shaped nuclei.
  • SSAs with nuclear atypia may be referred to as advanced sessile serrated adenomas.
• Submucosal lipomas seem to be associated with SSA in some way.^{[citation needed]}

DDx

• Hyperplastic polyp.
• Tubular adenoma - for SSA with dysplasia, TAs often less than 1 cm (uncommon for SSAs).

Images

• 

  SSA - low mag. (WC/Nephron)

• 

  SSA - intermed. mag. (WC/Nephron)

• 

  SSA - high mag. (WC/Nephron)

• 

  SSA - low mag. (WC/Nephron)

• 

  SSA - intermed. mag. (WC/Nephron)

• 

  SSA - very high mag. (WC/Nephron)

Sign out

POLYP, CECUM, POLYPECTOMY: 
- SESSILE SERRATED ADENOMA.
-- NEGATIVE FOR DYSPLASIA.

POLYP, ASCENDING COLON, POLYPECTOMY: 
- SESSILE SERRATED ADENOMA.
-- NEGATIVE FOR DYSPLASIA.

POLYP, HEPATIC FLEXURE OF COLON, POLYPECTOMY: 
- SESSILE SERRATED ADENOMA.
-- NEGATIVE FOR DYSPLASIA.

Dysplasia present

POLYP, ASCENDING COLON, POLYPECTOMY: 
- SESSILE SERRATED ADENOMA WITH DYSPLASIA.

The above exactly mirrors the Canadian consensus.

Management

The Canadian Partnership Against Cancer (2011) advocates the following statement:

Sessile serrated adenomas with dysplasia are considered to be advanced lesions that 
have an increased propensity to transform to adenocarcinoma. Complete endoscopic removal 
is recommended. If complete endoscopic removal cannot be achieved, short-term re-endoscopy
and biopsy, or surgical resection should be considered.

Micro

The section shows a small polypoid fragment of colonic mucosa with a serrated epithelium that focally extends to the crypt base. Several dilated crypt bases are seen. One horizontal crypt and one boot-shaped crypt are present. The epithelium matures to the surface. A small amount of submucosa is present and contains a benign lymphoid aggregate.