What are the parts of the fallopian tube in a female of reproductive age?

Anatomical Parts of the Fallopian Tube

The fallopian tube consists of four distinct anatomical segments from proximal to distal: the interstitial (intramyometrial) segment, the isthmus, the ampulla, and the infundibulum with its fimbrial end. 1

Detailed Anatomical Segments

Interstitial Segment

• The interstitial segment is the portion of the fallopian tube that traverses through the myometrium of the uterus, connecting the endometrial cavity to the more distal tubal segments 1
• This segment is also referred to as the intramyometrial portion of the tube 1
• On imaging, intervening myometrium can be visualized between a gestational sac in this location and the endometrium 1

Isthmus

• The isthmus is the narrow, straight segment immediately distal to the interstitial portion 2
• This segment has a smaller luminal diameter compared to the ampulla 3
• The isthmic region contains predominantly sympathetic innervation, particularly at the isthmo-ampullary junction 3
• Anatomically, the isthmus accounts for approximately 7% of ectopic pregnancy locations when specifically identified 2

Ampulla

• The ampulla is the longest and widest segment of the fallopian tube, extending from the isthmus to the infundibulum 1, 2
• This segment accounts for the majority (approximately 85%) of tubal ectopic pregnancies 2
• The ampullary region is the primary site where fertilization occurs 3
• The ampulla can be further subdivided into portions near the isthmus versus those closer to the infundibulum 2

Infundibulum and Fimbrial End

• The infundibulum is the funnel-shaped distal opening of the fallopian tube 1
• The fimbrial end represents the finger-like projections at the distal terminus of the tube 1
• These fimbriae are responsible for ovum pick-up from the ovary 3
• The fimbrial ends should be totally sampled in pathological examination to avoid missing disease 1
• Infundibular and fimbrial ectopic pregnancies account for approximately 7-8% of tubal pregnancies 2

Clinical Significance of Anatomical Terminology

When describing tubal pathology, precise anatomical location should be specified when clearly identifiable, though this is often not evident on ultrasound imaging. 1

• The terms isthmic, infundibular, or ampullary are optional descriptors for tubal ectopic pregnancies since precise location is typically not evident at ultrasound 1
• The interstitial segment requires specific identification as pregnancies in this location have different management implications 1
• Understanding these anatomical divisions is essential for surgical planning and pathological reporting 1