Acellular mucin in neoplastic and non-neoplastic conditions of the lower gastrointestinal tract

Table 1 Acellular mucin in neoplastic lower gastrointestinal tract conditions

Condition	Key features	Diagnostic implications	Prognosis
Mucinous adenocarcinoma	≥ 50% extracellular mucin, malignant epithelial cells	Confirm site via IHC (CK20, CDX2, SATB2)	Varies by site and molecular alterations
LAMNs/HAMNs	Abundant mucin, no infiltrative growth	Risk of pseudomyxoma peritonei	Generally favorable when organ-confined
SRCC	Signet ring cells	May represent metastasis	Poor prognosis
Serrated adenocarcinoma	Epithelial serration, minimal necrosis, clear or eosinophilic cytoplasm	CIMP (subset)	Unclear

IHC: Immunohistochemistry; CIMP: CpG island methylator phenotype; SRCC: Signet-ring cell carcinoma; LAMNs/HAMNs: Low/high-grade appendiceal mucinous neoplasms.

Table 2 Histologic differences between low grade appendiceal mucinous neoplasm vs non-neoplastic mucin-rich conditions in the appendix

Feature	LAMN	Non-neoplastic
Extent of disease	Extensive/circumferential involvement	Focal involvement
Crypt architecture	Loss of normal crypts	Preserved crypt architecture
Lamina propria	Attenuated lamina propria	Intact lamina propria
Muscularis mucosae	Diffusely thickened	Normal thickness
Epithelial villiform proliferation	Usually present	Absent
Lymphoid aggregates (lesional)	Usually absent	Usually present
Paneth cells (lesional)	Usually absent	Usually present
Inflammatory response	Usually sparse	Frequent periappendicitis and organized abscess

LAMN: Low-grade appendiceal mucinous neoplasm.

Table 3 Acellular mucin in non-neoplastic lower gastrointestinal tract conditions

Condition	Etiology	Histological findings	Clinical considerations
Appendicitis	Mucin translocation via diverticula or mural defect, common in interval appendectomy	Mucin pools within inflammatory background without epithelial dysplasia	Can mimic LAMN
Colonic diverticulitis	Mural defect, high luminal pressure	Mucin pools following distribution of diverticular pouch	Additional work up to rule out mucinous neoplasia may be required
Crohn’s disease	Mural defect due to prior surgery or fistula	Mucin pools at the site of mural defect	Findings need to be interpreted in an appropriate clinical context
Volvulus	High luminal pressure and microscopic mural defect	Mucin displaced into bowel wall	Findings need to be interpreted in an appropriate clinical context

LAMN: Low-grade appendiceal mucinous neoplasm.