Primary neoplasms of the hollow organs of the gastrointestinal tract. Staging and follow-up. The number of imaging modalities available to stage and follow-up patients with primary neoplasms of the gastrointestinal (GI) tract continues to increase. Magnetic resonance imaging (MRI), computed tomography (CT), and ultrasonography are useful techniques for both staging and follow-up. For staging, CT is most frequently used for the detection of liver metastases and is increasingly used as a substitute for the chest radiograph in the detection of lung metastases. CT is still the imaging test of choice for the preoperative staging of esophageal carcinoma. CT is less helpful in staging the patient with gastric carcinoma or colorectal carcinoma. The current usefulness of MRI in the staging of GI tract malignancies is limited by the lack of an adequate oral intraluminal contrast agent and degradation of images due to motion. Sonography, especially the new technique of endoscopic ultrasound, is promising for the detection of local invasion from GI tract malignancies. CT is used in the follow-up of patients with tumors of the GI tract to detect liver, adrenal, and nodal metastases as well as local recurrence because of the ability of CT to detect extraluminal masses. CT of the pelvis has been recommended as a routine follow-up procedure in patients who have undergone abdominal-peroneal resection. Both CT and MRI can be used to detect local recurrence, but suffer from the inability to differentiate scar from recurrent tumor. The initial hope that MRI would be capable of differentiating postoperative scar tissue from recurrent tumor has not been realized. Therefore, with positive CT or MRI findings, occasionally a percutaneous biopsy will be required to confirm local recurrence. 