{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,19]],"date-time":"2026-06-19T00:52:26Z","timestamp":1781830346450,"version":"3.54.5"},"reference-count":15,"publisher":"Springer Science and Business Media LLC","license":[{"start":{"date-parts":[[2026,6,18]],"date-time":"2026-06-18T00:00:00Z","timestamp":1781740800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"},{"start":{"date-parts":[[2026,6,18]],"date-time":"2026-06-18T00:00:00Z","timestamp":1781740800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"}],"content-domain":{"domain":["link.springer.com"],"crossmark-restriction":false},"short-container-title":["Anat Sci Int"],"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>The umbilicus is a distinct anatomical feature of the anterior abdominal wall, characterized by persistent postnatal depression. Despite its clinical and surgical relevance, the histological and spatial structures underlying the umbilical concavity remain unclear. Herein, we investigated the fibrous connective tissue underlying the umbilical concavity.\u00a0Five formalin-fixed cadaveric specimens (mean age: 77.4 years) were used. Two were used for macroscopic dissection, two for histological examination, and one for quasi-continuous serial sectioning with three-dimensional reconstruction.\u00a0Macroscopic dissection revealed a vertically cylindrical fibrous structure extending from the umbilical fossa to the anterior rectus sheath. Histological analysis confirmed that this structure enclosed a small fat compartment distinct from subcutaneous fat, representing an extraperitoneal fat protrusion in contact with the underside of the umbilical skin. Serial sections and three-dimensional reconstruction identified a tunnel-like fibrous structure, termed \u201cumbilical sheath,\u201d enveloping the protruded fat and bridging the umbilical ring and dermis. This sheath connected the invaginated skin to the linea alba and rectus sheath.\u00a0We identified a previously undescribed fibrous structure, the umbilical sheath, enclosing a localized protrusion of extraperitoneal fat, maintaining umbilical concavity. Recognition of this structure may guide optimal port placement and promote abdominal wall closure techniques that preserve anatomical support, potentially reducing incisional hernia risk.<\/jats:p>","DOI":"10.1007\/s12565-026-00950-w","type":"journal-article","created":{"date-parts":[[2026,6,18]],"date-time":"2026-06-18T11:51:53Z","timestamp":1781783513000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Why is the umbilicus concave? A histological and three-dimensional anatomical study revealing the \u201cumbilical sheath\u201d"],"prefix":"10.1007","author":[{"given":"Satoru","family":"Muro","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toshiro","family":"Tanioka","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Niina","family":"Hirano","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tong","family":"Liu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akimoto","family":"Nimura","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yusuke","family":"Kinugasa","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keiichi","family":"Akita","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,6,18]]},"reference":[{"key":"950_CR1","doi-asserted-by":"publisher","first-page":"394","DOI":"10.1055\/s-0040-1721869","volume":"53","author":"MA Abdulla","year":"2020","unstructured":"Abdulla MA, Fahad SMA (2020) Anthropometric determinations of umbilical position in Iraqi adults. Indian J Plast Surg 53:394\u2013398. https:\/\/doi.org\/10.1055\/s-0040-1721869. Available","journal-title":"Indian J Plast Surg"},{"key":"950_CR2","doi-asserted-by":"publisher","first-page":"46","DOI":"10.1177\/1553350618797619","volume":"26","author":"M Asakuma","year":"2019","unstructured":"Asakuma M, Komeda K, Yamamoto M, Shimizu T, Iida R, Taniguchi K, Inoue Y, Hirokawa F, Hayashi M, Okuda J, Kondo Y, Uchiyama K (2019) A concealed natural orifice: umbilicus anatomy for minimally invasive surgery. Surg Innov 26:46\u201349. https:\/\/doi.org\/10.1177\/1553350618797619","journal-title":"Surg Innov"},{"key":"950_CR3","first-page":"170","volume":"64","author":"RC Begg","year":"1930","unstructured":"Begg RC (1930) The urachus: its anatomy, histology and development. 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After death, informed consent was obtained from the donors\u2019 families, and no objections were raised.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Consent to participate"}}]}}