Diagnosis involves a combination of clinical evaluation and diagnostic tests. Initial assessment includes history and physical examination focusing on symptoms like vomiting and abdominal distension. Imaging studies such as abdominal X-rays and ultrasound can reveal stomach dilation. Upper gastrointestinal endoscopy is crucial to directly visualize the obstruction and obtain biopsies if needed. Additional tests like CT scan or barium meal studies may be used to determine the cause and extent of the blockage.