Table 2:

Variants and Pitfalls of PET/CT in GI cancers

Site	Tracer Used	Benign Conditions that can Mimic Malignancy	Malignant Conditions with Unreliable or Low-Grade Uptake
Esophagus	FDG	Esophagitis, leiomyoma	T-staging is unreliable Early-stage adenocarcinoma can be low-grade with low PPV for Stage 1 disease
			Radiation induced fibrosis or inflammation versus residual disease can have similar appearance
Stomach	FDG	Physiologic uptake, particularly within the fundus, gastritis, schwannoma, leiomyoma	Distal gastric tumors ca be low-grade compared to proximal tumors Decreased sensitivity for LNs Decreased sensitivity for diffuse-type cancers such as Signet ring cell cancers Decreased sensitivity for some indolent NHL such as gastric MALT
			Response assessment not possible for non-avid or minimally avid tumors Higher sensitivity for determining treatment failure than to predict response for GIST
			Role is unclear in routine follow up Can have false positive results
Small Bowel	FDG	Physiologic uptake, IBD, enteritis,	Can be low-grade for MALT lymphoma and neuroendocrine tumors (NET)
	Ga-DOTATATE		High proliferation index and poorly differentiated NETs and neuroendocrine carcinomas
Colon and Rectum	FDG	Physiologic uptake, metformin bowel, colonic or ileostomy stoma, polyps, diverticulitis, IBDs, colitis, Inflammatory pseudotumor, sarcoidosis, normal appendix	May not be helpful in staging of localized disease without metastases Mucinous tumors can be low-grade
		Anastomotic uptake – physiological and inflammation Post-operative changes and complications such as fistula Radiation induced inflammation	Can have false positive results for response assessment in neoadjuvant setting
			Not recommended for routine follow up; can have false positive results
Anal Canal	FDG	Physiological, hemorrhoids, anal fistulas	Not for local staging of primary tumor
		Radiation induced inflammation	Can be false positive if performed soon after chemoradiotherapy
			Role in follow up unclear – uptake within the anal canal on follow up does not necessarily indicate recurrence
Peritoneum	FDG	Benign conditions as such mesenteric panniculitis, post-operative changes, TB peritonitis Splenules, transposed ovaries, sarcoidosis, portal vein thrombosis, mesh prosthesis, hernia repair plug,	Decreased sensitivity for small-volume disease, predominantly cystic disease, ascites, multicystic peritoneal mesothelioma, pseudomyxoma peritonei
		Post hyperthermic intraperitoneal chemotherapy (HIPEC) or operative changes	Response assessment and recurrence – PET/CT may underestimate disease