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Additional imaging for staging is necessary as contrast x-ray studies and endoscopy alone are often inaccurate for staging esophageal cancer because the extent of local invasion and presence of regional nodal and distant metastases cannot be determined. CT imaging has provided a nonoperative way to stage esophageal cancer. The standard CT imaging protocol for esophageal cancer involves the use of oral and intravenous contrast with examination from the upper chest to the upper abdomen, including the entire liver. The overall accuracy of CT for staging esophageal cancer is excellent for advanced disease. Liver metastases and findings consistent with adjacent organ invasion can be reliably noted on CT scan as well as by MRI. The sensitivity and specificity for detecting bronchotracheal and pericardial invasion exceed 90-95% in most series. However, CT imaging does not reliably detect local and regional lymph node metastases and "early" (T1-T2) tumors.

The advent of EUS offers the most significant advance in the preoperative staging of esophageal cancer. EUS is performed using a modified upper endoscope with an ultrasound transducer housed within the tip. At frequencies ranging from 7.5 to 12 MHz, EUS depicts five layers of the esophageal wall corresponding to its distinct histologic layers (Figure 18-2). Malignant tumors are identified as hypoechoic masses with irregular margins that disrupt the normal esophageal architecture. The depth of tumor invasion is defined by the outermost margin of the hypoechoic mass (Figure 18-3). Suspicious appearing lymph nodes are identified as hypoechoic rounded structures within the mediastinum and near the esophagus (Figure 18-4). Fine needle aspiration (FNA) biopsies of lymph nodes can be obtained through some EUS scopes for definitive diagnosis of malignant involvement (Figure 18-5). EUS can accurately diagnose early cancers, that is, those classified as T1-T2 (Figures 18-6 and 18-7). The overall accuracy of EUS for predicting the extent of esophageal cancers approaches 80-90% for T and 70-80% for N classification.

There are several limitations of EUS for staging esophageal cancer that need to be recognized. Overstaging of a T2 lesion can sometimes happen when there is significant peritumoral inflammation, whereas understaging sometimes occurs largely due to microscopic invasion beyond the muscularis propria. EUS is also very reliable in diagnosing adjacent organ invasion (ie, invasion to pleura or aorta) (Figures 18-8 and 18-9); however, limited depth of penetration of EUS results in incomplete assessment for distant metastases. In addition, about 30% of esophageal cancers produce severe esophageal obstruction and cannot be traversed with the regular ultrasound endoscope at the time of presentation. Generally, these tumors can be accurately staged with EUS after dilation of the stricture; and when this occurs, they are almost always advanced tumors, that is, T3 or greater (Figure 18-10). Recently, the development of through-the-scope miniprobes and wire-guided small-diameter blind ultrasound probes has overcome the problems with tumor strictures in most cases. In addition, as these small caliber ultrasound probes utilize higher scanning frequencies (12-20 MHz), the detection and accuracy of staging for T2 tumors has improved significantly.

A large number of studies have looked into the staging accuracy of EUS and CT scan. It has been demonstrated that EUS is more accurate than CT scan for locoregional staging (both T and N classification). EUS appears to be superior in defining abdominal lymph node metastases (especially celiac axis nodes), although CT scan is still the better imaging study to detect distant organ metastases. Nonetheless, CT scan should be considered as complementary to EUS and should be combined with EUS to determine the extent of extraesophageal invasion into the mediastinum and distant metastases. The ideal algorithm for managing these patients should include a CT scan of chest and abdomen, and, if negative for metastasis, an EUS should be done to rule out locally advanced disease.

A few other diagnostic tools have also been employed to assist in the staging of esophageal cancer. Bronchoscopy is widely used for assessment of bronchial invasion, primarily in mid-esophageal tumors. Although bronchial invasion is common, invasion into the bronchial lumen is rare. Therefore, bronchoscopy generally provides only indirect evidence of bronchial invasion, such as luminal indentation or narrowing. Diagnostic laparoscopy has been utilized in the assessment of peritoneal metastases. It offers the advantage of tissue biopsy under direct vision and an access for laparoscopic ultrasound. Thoracoscopy has also been used to better assess mediastinal and pulmonary metastases.

Differential Diagnosis

The differential diagnosis of patients with dysphagia or odynophagia includes esophageal mucosal diseases, motility disorders, and benign and malignant obstructing lesions. The insidious onset of progressive dysphagia to solids and then to liquids with associated weight loss in patients over 40-50 years of age almost invariably points to esophageal cancer. Patients with benign obstructing lesions of the esophagus, such as benign peptic strictures, webs and rings, and achalasia, may present with features resembling esophageal cancer. Barium esophagram offers indirect evidence for benign versus malignant processes; however, endoscopy with biopsies should still be employed to distinguish benign from malignant disease.

Achalasia is a motility disorder with impaired relaxation of the lower esophageal sphincter and aperistalsis of the esophageal body. The classic radiographic appearance on the barium esophagram is a smooth, tapered distal esophagus referred to as a "bird's beak" appearance. Tumors at the gastroesophageal junction may at times mimic the signs, symptoms, and manometric findings of achalasia. Hence, endoscopy is required in all patients with suspected achalasia to exclude undiagnosed malignancy ("pseudoachalasia").

Malignant tumors of the esophagus other than squamous cell carcinoma and adenocarcinoma are exceedingly rare. These tumors usually cannot be distinguished based on clinical grounds and require histologic confirmation. Mucoepidermoid carcinoma and cystic adenoid carcinoma of the esophagus are rare yet extremely aggressive and can be missed on endoscopic biopsy due to their primarily submucosal growth pattern.