The aim of this study is to evaluate the role of endoscopic ultrasound (EUS) in the diagnosis of mediastinal and gastrointestinal subepithelial lesions.

The study also aims to assess the diagnostic accuracy of endoscopic ultrasound (EUS) elastography in differentiating benign from malignant mediastinal and gastrointestinal subepithelial lesions.

Endoscopic ultrasound (EUS), which combines ultrasonography and endoscopy, was developed approximately four decades ago and is now an established diagnostic tool for evaluating pancreatic, biliary, and gastrointestinal diseases. Although initially introduced as a purely diagnostic technique, technological advancements have enabled its evolution into a therapeutic modality. These developments have allowed EUS to facilitate cytological and histological diagnoses. In addition, the introduction of advanced imaging technologies, such as EUS elastography and contrast-enhanced harmonic EUS, has further improved real-time tissue characterization during endoscopic examination.

Mediastinal lesions are tumors that originate from, or extend into, the mediastinum. They may also represent metastatic deposits from extrathoracic primary tumors. These lesions encompass a broad histopathologic and radiologic spectrum, ranging from benign cystic and inflammatory conditions to highly aggressive malignant tumors. Mediastinal lesions represent a relatively uncommon but clinically significant group of pathologies, accounting for a small percentage of thoracic masses detected in imaging studies.

Mediastinoscopy remains a well-established diagnostic and staging tool, particularly for mediastinal lymphadenopathy. However, it is an invasive procedure associated with considerable cost, morbidity, and potential procedure-related complications, which may range from minor adverse events to severe and life-threatening complications. Therefore, there is a need for a less invasive yet reliable diagnostic modality. Endoscopic ultrasound offers a safer alternative for evaluating mediastinal pathology and guiding therapeutic decision-making.

For mediastinal lesions, EUS-especially when combined with fine-needle aspiration (FNA) or fine-needle biopsy (FNB)-provides a minimally invasive approach to evaluate and obtain tissue samples from lesions located in the posterior mediastinum. This approach may reduce the need for surgical diagnostic procedures. It is particularly useful for diagnosing lesions of unknown origin, staging mediastinal lymph nodes in lung cancer, and identifying inflammatory or granulomatous diseases such as tuberculosis.

Subepithelial lesions of the gastrointestinal tract present a diagnostic challenge because of their heterogeneous nature and variable clinical presentation. These lesions arise beneath the mucosal layer, originating from the muscularis mucosa, submucosa, or muscularis propria. They are often discovered incidentally during routine endoscopy or radiologic imaging. Although most subepithelial lesions are small and asymptomatic, they may occasionally cause dysphagia, gastrointestinal bleeding, or compressive symptoms. Their biological behavior ranges from benign and indolent to malignant and potentially aggressive neoplasms, such as gastrointestinal stromal tumors and neuroendocrine tumors.

Endoscopic ultrasound is currently considered one of the most effective imaging techniques for characterizing subepithelial lesions. It provides detailed information regarding the layer of origin, size, echogenicity, vascularity, and relationship to adjacent structures. Endoscopic ultrasound-guided fine-needle aspiration or fine-needle biopsy enables cytologic or histologic confirmation of the lesion's nature. In addition, EUS elastography enhances the diagnostic capability of conventional EUS by providing real-time assessment of tissue stiffness, which may help differentiate benign from malignant lesions.

EUS elastography can be performed using strain elastography or shear wave elastography techniques. Strain elastography evaluates tissue deformation in response to external compression, whereas shear wave elastography measures shear wave velocity as an indirect indicator of tissue stiffness. Although most research has focused on pancreatic masses, emerging evidence suggests potential applications in mediastinal lymph nodes and gastrointestinal subepithelial lesions.

Inclusion Criteria:

• Age: Adults ≥ 12 years.

  • Clinical indication: Patients referred for diagnostic EUS of a 1_mediastinal mass or mediastinal lymphadenopathy detected on prior imaging (CT/MRI) .

    2- subepithelial lesions lesion detected by endoscopy .

  • Lesion accessibility: Lesion judged by the endosonographer to be accessible to EUS imaging and elastography and amenable to EUS-guided sampling

Exclusion Criteria:

• • patient Refusal or inability to provide informed consent

  • Uncorrectable coagulation disorder
  • Presence of contraindicating endoscopy/sedation
  • Lesion inaccessible to EUS or elastography (e.g., too far from the esophagus/airway to obtain reliable elastography or visualization) as judged by the performing endosonographer.

Patients referred for diagnostic EUS of a 1_mediastinal mass or mediastinal lymphadenopathy detected on prior imaging (CT/MRI) .

2- subepithelial lesions lesion detected by endoscopy .