<p>A tadpole-shaped appendix has been described as a characteristic morphology of appendiceal mucinous lesions, but its clinical and ultrasonographic significance has not been fully clarified. We report a case of low-grade appendiceal mucinous neoplasm (LAMN) in which a tadpole-shaped appendiceal lesion acted as the leading point of extensive intestinal intussusception. A woman in her 60s presented with abdominal pain and difficulty with defecation. Abdominal ultrasonography demonstrated extensive intestinal intussusception extending to the transverse colon. At the leading point, the long-axis view showed a tadpole-shaped configuration composed of a spherical cystic dilated portion and a contiguous tubular structure. Dynamic observation suggested that these findings represented a single continuous appendiceal structure rather than separate cystic lesions. The short-axis view of the same structure showed a multilayered concentric ring appearance. Surgical and histopathologic examination established the diagnosis of appendiceal intussusception associated with LAMN, with secondary intestinal intussusception. Although prior or serial imaging was not available to directly demonstrate temporal progression from appendiceal to intestinal intussusception, previous reports have described appendiceal mucinous lesions with tadpole-shaped or cup-and-ball morphology as the leading point of intussusception. Therefore, when this morphology is identified on ultrasonography, careful assessment for appendiceal or intestinal intussusception is warranted. Recognition of this morphology and its continuity on ultrasonography may serve as a practical diagnostic clue and contribute to preoperative diagnosis and appropriate surgical management.</p>