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Gastric Tumours: Complete Radiology Reference

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1. NORMAL PERIGASTRIC ANATOMY

Stomach on Imaging

• Areae gastricae: fine reticular network of mucosal tufts separated by sulci (2-3 mm antrum, 3-5 mm body/fundus) - seen in ~70% patients
• Gastric rugae: smooth folds 3-5 mm thick, parallel to long axis, comprise mucosa + submucosa

Perigastric Ligaments & Stomach Bed

• Pancreatic body/tail (most important)
• Left kidney and left adrenal
• Splenic vessels and spleen
• Transverse mesocolon
• Left crus of diaphragm

Lymph Node Stations (Japanese Gastric Cancer Association)

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2. GASTRIC CARCINOMA

• Intestinal type: gland-forming, H. pylori-associated, better prognosis, FDG-avid
• Diffuse type (signet ring): no gland formation, infiltrates wall, linitis plastica, FDG-negative
• Mixed

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3. EARLY GASTRIC CANCER (EGC)

Japanese Morphological Classification:

CT Features (MDCT):

• Focal thickening of the inner mucosal layer only
• Abnormal focal mucosal hyperenhancement on arterial phase
• Preservation of outer hypodense stripe (submucosa) - the key T1 sign
• Clear perigastric fat plane
• T1 lesions without thickening are extremely difficult to detect; surface-shaded display or virtual gastroscopy (VG) may demonstrate them
• EUS is superior to CT for T1/T2 distinction

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4. ADVANCED GASTRIC CANCER (AGC)

Borrmann Classification:

CT Features:

• Polypoid: irregular mass; shelf sign (acute angle to wall = mucosal origin)
• Ulcerative: malignant ulcer sits WITHIN the gastric wall/mass (not projecting beyond wall); irregular nodular fold convergence (clubbed, amputated); no Hampton's line
• Linitis plastica (scirrhous/Borrmann IV): diffuse thickening, loss of rugae, rigid non-distensible "leather bottle" stomach, perigastric fat stranding
• Antral carcinoma: may cause gastric outlet obstruction

Benign vs Malignant Ulcer:

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5. TNM STAGING (AJCC 8th Edition)

T Stage:

N Stage:

M Stage:

• M1 = any distant mets (liver first, then peritoneum, lung, adrenal, bone, Krukenberg ovary)
• Positive peritoneal cytology = M1
• Para-aortic nodal disease = M1

Imaging by Stage:

• T3: haziness/stranding in fat; outer wall irregular
• T4a: serosal nodularity; loss of outer definition
• T4b: loss of fat plane + adjacent organ deformity

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6. PET-NEGATIVE TUMOURS & PATHOLOGY

Gastric Carcinoma Subtypes That Are PET-Negative:

1. Mucinous adenocarcinoma - mucin lakes with sparse metabolically active cells
2. Signet ring cell carcinoma - poorly differentiated, discohesive, low metabolic density
3. Poorly differentiated adenocarcinoma
4. Diffuse type (Lauren) overall
5. Low-grade MALToma

PET Limitations in Gastric Cancer (from Grainger & Allison):

1. Intense variable physiological uptake in normal gastric wall (masks small primaries)
2. Poor spatial resolution for N1/N2 (perigastric nodes too close to primary)
3. Better for N3 distant nodes (high specificity)
4. Metabolic response in FDG-avid tumours identifies therapy responders earlier than morphology

Other PET-Negative Gastric Pathologies:

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7. MESENCHYMAL TUMOURS

GIST (Gastrointestinal Stromal Tumour)

• Submucosal/extraluminal (exophytic) growth pattern
• Small tumours: homogeneous, well-defined, uniform enhancement
• Large/malignant tumours: heterogeneous, central necrosis/haemorrhage/cystic change
• Ulceration of overlying mucosa ("rose-thorn" or endoluminal niche)
• No lymph node metastasis (key feature - distinguishes from carcinoma and lymphoma)
• Liver mets (haematogenous) and peritoneal spread - NO lymph node spread
• Pseudo-progression on imatinib (tumours become cystic/hypoattenuating) - use Choi criteria (density decrease >15% OR size >10%), not RECIST

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Gastric Lipoma

• Pathognomonic: Fat-density mass (HU -80 to -120) with thin capsule
• Most common in antrum (submucosal location)
• MRI: T1 bright, T2 bright, suppresses on fat saturation
• Compressible on fluoroscopy
• Benign; no malignant potential

Leiomyoma

• Smooth muscle tumour from muscularis propria or muscularis mucosae
• Most common at cardia / gastroesophageal junction
• CT: homogeneous, well-defined, mild-moderate enhancement; calcification ~10%
• CD117 negative, desmin/SMA positive - unlike GIST
• Smaller, no exophytic growth tendency, no necrosis

Glomus Tumour

• Extremely rare benign vascular tumour of modified smooth muscle (glomus body cells)
• Occurs almost exclusively in antrum (submucosal)
• CT pathognomonic feature: Intensely hypervascular, homogeneous, arterial phase enhancement (equal to or exceeding aorta)
• MRI: T2 very high signal, avid gadolinium enhancement
• Key differentiator from carcinoid: even more intensely vascular, more homogeneous

Paraganglioma

• Extra-adrenal chromaffin cell tumour; gastric location extremely rare
• MRI pathognomonic: "Salt and pepper" appearance on T2 (flow voids = pepper; haemorrhagic foci = salt)
• CT: hypervascular mass, intense arterial enhancement
• Ga-68 DOTATATE PET positive
• Malignancy only determined by metastatic spread, not histology

Schwannoma

• Rare; most common benign gastric neurogenic tumour
• CT: well-defined homogeneous submucosal mass; peripheral lymph node cuff is characteristic
• S100 positive, CD117 negative, CD34 negative

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8. GASTRIC LYMPHOMA

• Low-grade MALToma: H. pylori-associated (CagA protein), indolent; may regress with H. pylori eradication alone
• DLBCL: High-grade; may arise de novo or from MALToma transformation; aggressive

Imaging Features:

• CT: Diffuse or segmental mural thickening (often >2 cm), preserved perigastric fat planes (key differentiator)
• Homogeneous enhancement; bulky regional adenopathy
• Can cross the pylorus (unlike carcinoma which tends to respect it)
• Multiple submucosal nodules, ulcerations, polypoid masses on barium

Lymphoma vs Carcinoma on CT:

Dawson Criteria (Primary GI Lymphoma):

1. No peripheral lymphadenopathy at presentation
2. No mediastinal lymphadenopathy
3. Normal WBC and differential on peripheral blood
4. Predominantly bowel involvement with regional nodes only
5. No hepatic or splenic involvement (except by direct extension)

Lugano Classification (GI Lymphoma Staging):

Lugano 5-Point Deauville Scale (PET Response):

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9. CARCINOID / NEUROENDOCRINE TUMOUR (NET)

• CT: small hypervascular submucosal nodules (Types 1/2); large single mass (Type 3)
• Ga-68 DOTATATE PET is the modality of choice - FDG negative (G1/G2)
• G3 neuroendocrine carcinoma (NEC): FDG-positive

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10. CARCINOMA MIMICS

Ménétrier's Disease

• Foveolar cell hyperplasia, protein-losing enteropathy
• Barium/CT: Massively enlarged, bizarre lobulated folds - proximal stomach and greater curvature, classic antral sparing (antrum involved up to 50%)
• Folds remain pliable - key differentiator (carcinoma = rigid, aperistaltic)
• Increased small bowel fluid (protein-losing)
• Fibrosing variant mimics linitis plastica

Zollinger-Ellison Syndrome (ZES)

• Gastrinomas (75% pancreas, 15% duodenum); 50% malignant with liver mets
• Gastric imaging: Thickened folds + excess gastric secretions, multiple peptic ulcers (distal duodenum/jejunum - 4th part)
• CT: hypervascular pancreatic/duodenal mass; gastrinoma triangle
• Associated with MEN-1
• Ga-68 DOTATATE PET / Octreotide scan for tumour detection

Eosinophilic Gastritis

• Diffuse eosinophil infiltration in atopic/asthmatic patients
• CT: diffuse wall thickening, antral narrowing and rigidity, mucosal nodularity
• Eosinophilic ascites (serosal involvement)
• Peripheral eosinophilia

Amyloidosis

• Submucosal amyloid deposition
• CT: diffuse wall thickening, rigidity - mimics linitis plastica
• Non-specific; diagnosis by biopsy (Congo red staining, apple-green birefringence)

Corrosive Gastritis

• Acid ingestion: necrosis → fibrosis
• CT/barium late: severely deformed, contracted stomach ("tobacco pouch"), luminal narrowing down to duodenal bulb size

Gastric Varices

• Fundal submucosal nodular/serpiginous masses ("grape-like")
• CT/MRI: enhancing submucosal vessels on venous phase
• Efface with compression (pliable) - differentiates from neoplasm
• Portal hypertension context; absent oesophageal varices + gastric varices alone = splenic vein thrombosis (pancreatitis/pancreatic Ca)

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11. ECTOPIC PANCREATIC TISSUE

• Most common site: Antrum/pylorus, greater curvature, submucosal
• Pathognomonic barium/endoscopy finding: Submucosal mass with central umbilication (represents the ductal orifice)
• CT: isoattenuating to normal pancreas, ill-defined or well-defined, duct-like structure may be visible
• MRI: same signal characteristics as normal pancreatic tissue on all sequences
• Benign; rarely complicated by pancreatitis within the rest

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12. GASTRIC METASTASES

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13. COMPLETE DIFFERENTIAL DIAGNOSIS WITH DIFFERENTIATING FEATURES

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14. QUICK REFERENCE: PATHOGNOMONIC IMAGING SIGNS

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