Gastric cancer is the fifth most common cancer type worldwide and the third leading cause of cancer deaths (1). Radiological examination methods play an important role in the preoperative staging of gastric cancer, post-treatment restaging, and post-operative recurrence monitoring (2).

Endoscopic ultrasonography (EUS) is the preferred imaging method due to its high performance in demonstrating the layers of the stomach in early-stage tumors (3), and also there is a chance to perform biopsy with EUS.

In locally advanced cancers, clinical preoperative staging, investigation of distant metastasis and peritoneal implantation, post-treatment restaging, and post-operative recurrence follow-up are performed using primarily computed tomography (CT), positron emission tomography (PET-CT), and magnetic resonance imaging (MRI) (4).

CT

-After at least 8 hours of fasting

-Gastric distension (1000 ml water + 1000-250 ml osmolac mixture, 1000 ml Polyethylene Glycol (PEG) can also be used. 2% iodinated opaque or diluted barium mixture in 1000-1500 ml water as positive contrast)

-IV CONTRAST AGENT (100-120 ML NONIONIC CONTRAST AGENT, 2-3 M/SEC)POST-INJECTION arterial (40 sec) + portal phase (70 sec)

-MPR IMAGES

-T STAGE + N STAGE + METASTASIS

PET-CT

-Staging at diagnosis (determination of lymphatic and hematogenous metastases)

-Presence of peritoneal carcinomatosis

-Evaluation of treatment response

-Evaluation for recurrence

Endoscopic US is useful in detecting T and local N in early-stage tumors because it can separate the stomach layers from each other.

Whole body CT or MRI is performed to evaluate transserous findings and T4 stage tumors, the presence of local and distant LAP, the diagnosis of metastasis, and the determination of ascites fluid.

PET-CT is functionally helpful in determining occult metastasis and in post-treatment follow-up.

The success of EUS in antral tumors and PET-CT in mucinous tumors and diffuse tumors decreases.

Laparoscopy and irrigation detects small peritoneal and diaphragmatic implants that cannot be detected by cross-sectional scans.

It is reported that Dual Source CT examination is more successful in distinguishing T3-T4 when periserosal fat tissue involvement can be distinguished more clearly!!!

The prognostic factor that plays a fundamental role in the treatment of stomach cancer is the TNM classification system recommended by the American Joint Committee on Cancer (AJCC). According to the TNM classification of gastric cancer; T is used to define the depth of the tumor, N to define lymphatic involvement, and M to define the status of distant metastasis (5).

T stage

Definition

T1

T1a

Invasion of the lamina propria or muscularis mucosae

T1b

Invasion of the submucosa

T2

Invasion of the muscularis propria

T3

Invasion of the subserosal connective tissue without invasion of adjacent structures or serosa

T4

T4a

Invasion of serosa (visceral peritoneum)

T4b

Invasion of adjacent structures/organs

N stage

Definition

N0

No lymph node (LN)

N1

1-2 regional LN

N2

3-6 regional LN

N3

7 or more LN

N3a

7-15 LN

N3b

16 or more

N stage

Definition

N0

No lymph node (LN)

N1

1-2 regional LN

N2

3-6 regional LN

N3

7 or more LN

N3a

7-15 LN

N3b

16 or more

Regional lymph nodes: N category

    - Greater/lesser curvature

     - Around the left gastric, common hepatic, celiac and splenic arteries

      - Hepatoduodenal

    Distant LN: M category

- Retropancreatic

- Mesenteric

- Para-aortic

PATHOLOGICAL LYMPH NODE CRITERIA IN CT AND MRI

- perigastric lymph nodes with a short axis of more than 6-8 mm - Round configuration - Central necrosis - HETEROGENEUS / OBVIOUS contrast enhancement - Diffusion restriction in diffusion-weighted MR sectionsIn this poster, we aim to discuss the radiological features of gastric cancer and highlight the staging classification based on CT imaging.

M stage

Definition

M0

No metastasis

M1

Imaging-based detection of organ metastasis (including peritoneal)

Distant metastasis includes peritoneal seeding, positive peritoneal cytology and omental tumor not part of continuous extension.

Confirmation of peritoneal metastasis by diagnostic laparoscopy or peritoneal washings performed as part of the staging workup is considered as positive metastasis

• Gross evidence of metastasis seen during laparoscopy is cTcNcM1
• Positive washings obtained during laparoscopy without evidence of gross metastasis is cTcNpM1