Gastrointestinal Imaging

Which Imaging Study Is Best for Staging Newly Diagnosed Gastric Adenocarcinoma?

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Which Imaging Study Is Best for Staging Newly Diagnosed Gastric Adenocarcinoma?

A 68-year-old male presents to your clinic for oncology consultation. An esophagogastroduodenoscopy (EGD) with biopsy last week confirmed a diagnosis of gastric adenocarcinoma in the antrum. Before you can recommend a treatment plan—be it neoadjuvant therapy, upfront surgical resection, or systemic chemotherapy—you need to accurately stage the disease. The critical question is whether the cancer is confined to the stomach and regional lymph nodes or has already spread to distant sites like the liver or peritoneum. This article provides a clinical workflow for this exact scenario, guiding your choice of imaging for staging locoregional or distant metastases in an adult with newly diagnosed gastric adenocarcinoma. Based on the American College of Radiology (ACR) Appropriateness Criteria, the initial recommended study is CT abdomen and pelvis with IV contrast, which is rated Usually appropriate.

Who Fits This Clinical Scenario?

This guidance applies specifically to adult patients with a new, biopsy-proven diagnosis of gastric adenocarcinoma who require initial staging. The primary clinical goal is to determine the anatomic extent of the disease—the T (tumor), N (nodes), and M (metastases) stages—to inform the initial therapeutic strategy. This workflow is designed for the moment after the endoscopic diagnosis is made but before any treatment has been initiated.

It is crucial to distinguish this scenario from others that may seem similar but require a different diagnostic approach:

  • Initial Diagnosis: This article is NOT for a patient with vague symptoms like dyspepsia or weight loss who is being evaluated for a suspected gastric mass. That workup falls under the “Suspected gastric adenocarcinoma. Initial imaging” scenario, which has a different set of imaging considerations.
  • Post-treatment Evaluation: This guidance does NOT apply to patients who have already undergone chemotherapy, radiation, or surgery for gastric cancer. Assessing treatment response or looking for recurrence is a distinct clinical question covered in the “Posttreatment evaluation” and “Surveillance of gastric adenocarcinoma” scenarios.
  • Other Gastric Tumors: This workflow is tailored for adenocarcinoma, the most common type of gastric cancer. Other histologies, such as gastrointestinal stromal tumors (GIST) or lymphoma, have different patterns of spread and may have different optimal imaging protocols.

What Diagnoses Are You Working Up in This Scenario?

While the primary diagnosis of gastric adenocarcinoma is already established, the staging workup is essentially a differential diagnosis of disease extent. The imaging study is ordered to answer several key questions that will determine the patient’s prognosis and treatment path.

Locoregional Disease (T and N Stage): The first goal is to assess how deeply the tumor has invaded the gastric wall and whether it has spread to nearby lymph nodes. Imaging seeks to differentiate between early-stage disease confined to the stomach lining and locally advanced disease that has grown through the wall to involve adjacent organs (like the pancreas or colon) or has spread to regional perigastric, celiac, or hepatic artery lymph nodes. This distinction is critical for determining surgical resectability.

Distant Metastatic Disease (M Stage): The most consequential finding on a staging scan is the presence of distant metastases, which classifies the disease as Stage IV and typically precludes curative surgery. The imaging study must be sensitive for metastases in the most common sites. This includes hepatic metastases (the most frequent site of hematogenous spread), peritoneal carcinomatosis (diffuse seeding of the abdominal lining), and distant lymph node involvement beyond the regional basins. Less commonly, spread to the lungs, ovaries (Krukenberg tumor), or bone may occur.

Why Is CT Abdomen and Pelvis with IV Contrast the Recommended Study?

For the initial staging of gastric adenocarcinoma, the ACR designates CT abdomen and pelvis with IV contrast as Usually appropriate. This modality serves as the workhorse for staging due to its wide availability, rapid acquisition time, and comprehensive assessment of the anatomy relevant to gastric cancer.

The rationale for its high rating is threefold:
1. Comprehensive Anatomic Assessment: A contrast-enhanced CT (CECT) provides excellent detail of the gastric wall, allowing for assessment of tumor thickness and extension into adjacent fat and organs (T-staging). It is also the primary modality for identifying enlarged regional and distant lymph nodes (N-staging) and is highly effective at detecting common metastatic sites, particularly liver and peritoneal disease (M-staging).
2. Role of IV Contrast: Intravenous contrast is not optional; it is essential. The enhancement pattern helps delineate the tumor from the normal, avidly enhancing gastric mucosa. For M-staging, portal venous phase imaging is optimized for detecting hypovascular liver metastases, which are common from gastric primaries.
3. Efficiency and Accessibility: CT is a fast and widely accessible examination that provides the necessary information for the multidisciplinary tumor board to make timely treatment decisions.

How do alternative studies compare for this specific scenario?

  • FDG-PET/CT skull base to mid-thigh is also rated Usually appropriate. It is highly sensitive for detecting distant nodal and visceral metastases (M-stage) and can sometimes identify sites of spread missed by CT. However, it provides less detailed local anatomic information for T-staging compared to a dedicated multiphasic CT and can have false positives from inflammatory conditions. It is often used as an adjunct to CECT, especially in cases of locally advanced disease where confirming the absence of distant metastases is critical before proceeding with major surgery or neoadjuvant therapy.
  • MRI abdomen and pelvis without and with IV contrast is rated May be appropriate. MRI is not typically the first-line staging tool but serves as an excellent problem-solving modality. Its primary role is in characterizing indeterminate liver lesions found on CT or in patients with a contraindication to iodinated CT contrast.
  • Endoscopic Ultrasound (EUS) is rated Usually not appropriate by the ACR for the combined purpose of staging locoregional or distant metastases. This can be confusing, as EUS is the most accurate modality for determining the depth of tumor invasion (T-stage) and evaluating perigastric lymph nodes (N-stage). However, it is an invasive procedure and cannot assess for distant M-stage disease in the liver, peritoneum, or chest. Therefore, while EUS is a critical part of the overall staging paradigm for early or locally advanced disease, it does not replace cross-sectional imaging (CT or PET/CT) for a complete M-stage evaluation.

The radiation dose for a CT abdomen and pelvis is moderate (adult relative radiation level ☢☢☢, 1-10 mSv). This is a necessary trade-off for the critical diagnostic information gained, which directly impacts a major oncologic treatment decision.

Once you’ve decided on the comprehensive staging workup, which often includes imaging of the chest, our protocol guide covers the technique, contrast, and reading principles: CT Chest/Abdomen/Pelvis with IV Contrast.

What’s Next After CT Abdomen and Pelvis with IV Contrast? Downstream Workflow

The results of the staging CT will direct the patient into one of several distinct management pathways, typically decided in a multidisciplinary tumor board meeting.

  • If the CT shows clear evidence of distant metastases (M1 disease): The patient has Stage IV cancer. The primary treatment is systemic chemotherapy to control the disease, prolong survival, and palliate symptoms. Curative-intent surgery is generally not an option, although palliative procedures may be considered for bleeding or obstruction.
  • If the CT shows no distant metastases but locally advanced disease (e.g., T3/T4 or N-positive): The patient is a candidate for a curative-intent multimodal approach. This often involves neoadjuvant chemotherapy (or chemoradiotherapy) to downstage the tumor, followed by surgical resection (gastrectomy with lymphadenectomy). A PET/CT may be ordered in this situation to confirm the absence of occult distant disease before committing to aggressive local therapy.
  • If the CT shows early-stage, localized disease (e.g., T1/T2, N0, M0): The patient may be a candidate for upfront surgical resection. EUS is often performed in this cohort to more precisely define the T and N stage, which can help determine if endoscopic resection is feasible for very early (T1a) tumors.
  • If the CT is indeterminate for metastatic disease: An indeterminate finding, such as a small, nonspecific liver lesion, requires further investigation. The next step is often a problem-solving study like an MRI of the abdomen with IV contrast. If the finding remains suspicious after MRI, a biopsy may be necessary to confirm or rule out metastatic disease before finalizing the treatment plan.

Pitfalls to Avoid (and When to Get Help)

Accurate staging is paramount, and several common pitfalls can compromise the quality of the workup.

  • Omitting IV Contrast: Ordering a non-contrast CT is a critical error. It severely limits the evaluation of the primary tumor, lymph nodes, and, most importantly, solid organ metastases like those in the liver.
  • Inadequate Gastric Distention: A collapsed stomach can obscure a tumor or mimic pathologic wall thickening. Proper patient preparation with oral contrast (water or positive contrast, depending on institutional protocol) is key to distending the stomach for optimal evaluation.
  • Forgetting the Chest: Gastric cancer can metastasize to the lungs. While the ACR scenario focuses on the abdomen and pelvis, a complete staging workup almost always includes a concurrent CT of the chest.
  • Over-relying on CT for T-staging: While CT provides a good estimate, EUS is superior for differentiating T1/T2 from T3 disease. For borderline resectable cases, EUS is an invaluable complementary tool.

If the imaging findings are complex, equivocal, or suggest borderline resectability, the case should be presented at a multidisciplinary gastrointestinal tumor board. This forum allows for collaborative input from surgeons, oncologists, radiation oncologists, and radiologists to create the optimal, personalized treatment plan.

Related ACR Topics and Tools

This article is a deep dive into one specific clinical scenario. For a broader view of all related scenarios, including initial diagnosis and post-treatment surveillance, please consult our parent guide.

Frequently Asked Questions

Why is CT often preferred over FDG-PET/CT as the very first staging study?

While both are rated ‘Usually appropriate,’ a high-quality, contrast-enhanced CT is typically the initial workhorse because it provides superior anatomic detail of the primary tumor’s local invasion (T-stage) and its relationship to adjacent structures, which is critical for surgical planning. PET/CT excels at detecting distant metastases (M-stage) but has lower spatial resolution for local disease. Often, CT is performed first, and PET/CT is added if the patient has locally advanced disease to definitively rule out distant metastases before proceeding with curative-intent therapy.

What is the role of endoscopic ultrasound (EUS) if it’s rated ‘Usually not appropriate’ in this ACR scenario?

The ‘Usually not appropriate’ rating applies to using EUS as a standalone tool for the combined purpose of staging locoregional AND distant metastases. EUS cannot evaluate for distant disease in the liver, lungs, or peritoneum. However, EUS is the most accurate modality for local T-staging (depth of tumor invasion) and N-staging (perigastric nodes). It is a critical, complementary tool used in conjunction with CT or PET/CT, especially for early-stage cancers (to see if endoscopic resection is possible) or locally advanced cancers (to confirm resectability).

Do I need to order a separate CT of the chest for complete staging?

Yes, in most cases. The lungs are a potential site of metastatic disease from gastric cancer. While the primary ACR recommendation focuses on the abdomen and pelvis to assess the primary tumor and most common metastatic sites (liver, peritoneum), a complete staging workup for a potentially curable patient almost always includes a CT of the chest. This is often performed during the same imaging session as the CT abdomen and pelvis.

What if my patient has a severe allergy to iodinated contrast or renal failure?

In cases of a true contraindication to iodinated contrast, MRI of the abdomen and pelvis with and without a gadolinium-based contrast agent is a suitable alternative and is rated ‘May be appropriate.’ MRI is excellent for evaluating the liver for metastases. For patients who cannot receive any type of IV contrast, a non-contrast CT combined with an FDG-PET/CT can provide the necessary staging information, though evaluation of the primary tumor on the non-contrast CT will be limited.

How does this initial staging imaging differ from surveillance imaging after treatment?

Initial staging imaging aims to define the full anatomic extent of the disease at diagnosis to determine the first-line treatment plan. Surveillance imaging, performed after curative-intent treatment, has a different goal: to detect disease recurrence as early as possible. The ACR criteria for surveillance are a separate clinical scenario and may involve different imaging modalities or frequencies depending on the initial stage and type of treatment received.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026