Reproductive system · Pelvis · Female
Isthmus of uterine tube !
The isthmus is the narrow part of the uterine tube next to the uterus; it carries the embryo inward and is where tubes are usually tied for sterilisation.
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What it is
The narrow part of the tube next to the uterus.
What it does
Carries the embryo into the uterus; the usual place where a tube is tied or clipped for sterilisation.
Key facts
- Where
- Narrow, thick-walled medial third next to the uterus
- Function
- Embryo transport to the uterus; usual site of tubal occlusion (ligation, clips, rings)
Relations
- Medial
- Intramural part of the tube, crossing the uterine wall to open into the cavity at the cornu
- Lateral
- Ampulla of uterine tube
- Below
- Ovarian ligament and mesosalpinx
- In front
- Round ligament of uterus, beginning just below and in front
How to find it
At laparoscopy it is the firm, narrow, cord-like inner part of the tube next to the uterine corner. The round ligament starts just below and in front of it and looks similar, so the tube is followed out to its fimbriae before a sterilisation clip or ring is placed.
On imaging
On hysterosalpingography a block close to the uterus can be spasm rather than true occlusion; salpingitis isthmica nodosa shows as small contrast-filled outpouchings along the isthmus.
Common problems
- Ectopic pregnancy (a pregnancy that implants in the tube).
- Infection (pelvic inflammatory disease) that can scar and block the tubes and cause infertility.
How it is diagnosed
Ultrasound and a pregnancy hormone (hCG) test for ectopic pregnancy; tests of tubal patency for infertility.
Treatment
- Tubal ligation or removal of the tubes (salpingectomy) for permanent contraception.
- An ectopic pregnancy is treated with medicine (methotrexate) or surgery.
Clinical notes
- Ligation methods (cutting and tying a loop, clips, rings, bipolar coagulation) are applied to the isthmus, usually a few centimetres from the uterus
- When sterilisation fails, the resulting pregnancy is more likely to be ectopic
- Next to it, a pregnancy in the intramural part (interstitial ectopic) can grow larger before rupturing and then bleed severely, given the rich uterine blood supply
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Why is the isthmus of the uterine tube the usual site for tubal ligation?
It has a narrow lumen and thick muscular wall; reversal joining two isthmic ends works best because the diameters match.
Why does an isthmic ectopic pregnancy tend to rupture early and bleed heavily?
The isthmus has little room to stretch.
What is salpingitis isthmica nodosa?
Nodular thickening of the isthmus with small outpouchings of the lining, linked with infertility and ectopic pregnancy.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- isthmus tubae uterinae TA2 3492
- Official Spanish (DeCS)
- Istmo de la trompa uterina
- English (TA2)
- Isthmus of uterine tube
Related
Sources: Terminologia Anatomica (TA2); Anatomy, Abdomen and Pelvis: Fallopian Tube; 27.2 Anatomy and Physiology of the Ovarian Reproductive System (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.
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Representative model, for educational purposes only.
