{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,5]],"date-time":"2026-02-05T03:30:56Z","timestamp":1770262256428,"version":"3.49.0"},"reference-count":13,"publisher":"BMJ","issue":"2","license":[{"start":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T00:00:00Z","timestamp":1770163200000},"content-version":"unspecified","delay-in-days":3,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Rep"],"accepted":{"date-parts":[[2026,1,11]]},"published-print":{"date-parts":[[2026,2]]},"abstract":"<jats:p>Rudimentary horn pregnancy (RHP) is a rare form of ectopic pregnancy that poses significant risks if not recognised early, as rupture can result in severe maternal morbidity. Early diagnosis is both challenging and crucial. Ultrasound pattern recognition plays a central role in identifying RHP, with MRI serving as a valuable adjunct in suspicious cases. Here, we report a case of an unruptured RHP diagnosed in the early second trimester, following a failed medical termination attempt 6\u2009days prior due to early fetal demise. We present a step-by-step ultrasound diagnostic approach, emphasising the importance of recognising this rare condition. In rare instances, as illustrated in this case, a large unruptured RHP may be misdiagnosed as an intrauterine pregnancy or another form of ectopic pregnancy. This underscores the need for clinicians to be familiar with atypical image findings. Accurate diagnosis and precise localisation of the pregnancy are essential for optimal management.<\/jats:p>","DOI":"10.1136\/bcr-2025-267436","type":"journal-article","created":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T14:55:30Z","timestamp":1770216930000},"page":"e267436","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Step-by-step ultrasound guide for rudimentary horn pregnancy diagnosis"],"prefix":"10.1136","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0980-2128","authenticated-orcid":false,"given":"Kuntharee","family":"Traisrisilp","sequence":"first","affiliation":[{"name":"Obstetrics and Gynecology, ChiangMai University, Muang, Chiang Mai, Thailand"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dhammapoj","family":"Jeerakornpassawat","sequence":"additional","affiliation":[{"name":"Obstetrics and Gynecology, ChiangMai University, Muang, Chiang Mai, Thailand"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Natpat","family":"Jansaka","sequence":"additional","affiliation":[{"name":"Obstetrics and Gynecology, ChiangMai University, Muang, Chiang Mai, Thailand"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2026,2,4]]},"reference":[{"key":"2026020406552086000_19.2.e267436.1","doi-asserted-by":"crossref","DOI":"10.21037\/acr-23-164","article-title":"Imaging diagnosis of rudimentary horn pregnancy: a case report","volume":"8","author":"Ji","year":"2024","journal-title":"AME Case Rep"},{"key":"2026020406552086000_19.2.e267436.2","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1080\/14767058.2017.1387533","article-title":"Tale of rudimentary horn pregnancy: case reports and literature review","volume":"32","author":"Yassin","year":"2019","journal-title":"J Matern Fetal Neonatal Med"},{"key":"2026020406552086000_19.2.e267436.3","doi-asserted-by":"crossref","first-page":"687","DOI":"10.1007\/s00404-012-2625-7","article-title":"Rudimentary horn pregnancy: a 10-year experience and review of literature","volume":"287","author":"Siwatch","year":"2013","journal-title":"Arch Gynecol Obstet"},{"key":"2026020406552086000_19.2.e267436.4","doi-asserted-by":"publisher","DOI":"10.1097\/01.AOG.0000161321.94364.56"},{"key":"2026020406552086000_19.2.e267436.5","doi-asserted-by":"crossref","first-page":"23","DOI":"10.4103\/0019-5359.29594","article-title":"Unruptured postdated pregnancy with a live fetus in a noncommunicating rudimentary horn","volume":"61","author":"Goel","year":"2007","journal-title":"Indian J Med Sci"},{"key":"2026020406552086000_19.2.e267436.6","doi-asserted-by":"publisher","DOI":"10.1093\/humrep\/dev264"},{"key":"2026020406552086000_19.2.e267436.7","doi-asserted-by":"crossref","unstructured":"Obaid M , Abu-Faza M , Abdelazim IA . Cornual or interstitial ectopic pregnancy? Am J Obstet Gynecol 2024;231. doi:10.1016\/j.ajog.2024.05.052","DOI":"10.1016\/j.ajog.2024.05.052"},{"key":"2026020406552086000_19.2.e267436.8","doi-asserted-by":"crossref","first-page":"2531","DOI":"10.1016\/j.radcr.2023.04.028","article-title":"Distinguishing between cornual, angular and interstitial ectopic pregnancy: A case report and a brief literature review","volume":"18","author":"Dhanju","year":"2023","journal-title":"Radiol Case Rep"},{"key":"2026020406552086000_19.2.e267436.9","doi-asserted-by":"crossref","first-page":"2247","DOI":"10.1002\/jum.16540","article-title":"Ultrasound Classification and Preoperative Ultrasound Diagnosis Analysis of Ovarian Ectopic Pregnancy","volume":"43","author":"Lv","year":"2024","journal-title":"J Ultrasound Med"},{"key":"2026020406552086000_19.2.e267436.10","article-title":"Abdominal Ectopic Pregnancy: A Case Report and Literature Review","volume":"17","author":"Eisa","year":"2025","journal-title":"Cureus"},{"key":"2026020406552086000_19.2.e267436.11","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1007\/s10140-021-01974-7","article-title":"Ectopic pregnancy: a resident\u2019s guide to imaging findings and diagnostic pitfalls","volume":"29","author":"Houser","year":"2022","journal-title":"Emerg Radiol"},{"key":"2026020406552086000_19.2.e267436.12","doi-asserted-by":"publisher","DOI":"10.1002\/uog.5131"},{"key":"2026020406552086000_19.2.e267436.13","doi-asserted-by":"crossref","first-page":"904","DOI":"10.2214\/AJR.13.10644","article-title":"Beyond ultrasound: CT and MRI of ectopic pregnancy","volume":"202","author":"Kao","year":"2014","journal-title":"AJR Am J Roentgenol"}],"container-title":["BMJ Case Reports"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.1136\/bcr-2025-267436","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T14:55:32Z","timestamp":1770216932000},"score":1,"resource":{"primary":{"URL":"https:\/\/casereports.bmj.com\/lookup\/doi\/10.1136\/bcr-2025-267436"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,2]]},"references-count":13,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2026,2,4]]},"published-print":{"date-parts":[[2026,2]]}},"alternative-id":["10.1136\/bcr-2025-267436"],"URL":"https:\/\/doi.org\/10.1136\/bcr-2025-267436","relation":{},"ISSN":["1757-790X"],"issn-type":[{"value":"1757-790X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,2]]}}}