H and M lines (pelvic floor)

Last revised by Yuranga Weerakkody on 11 Dec 2023

Citation, DOI, disclosures and article data

Citation:

Shah V, Weerakkody Y, Bell D, et al. H and M lines (pelvic floor). Reference article, Radiopaedia.org (Accessed on 19 Apr 2024) https://doi.org/10.53347/rID-81514

DOI:

https://doi.org/10.53347/rID-81514

Permalink:

https://radiopaedia.org/articles/81514

rID:

81514

Article created:

26 Aug 2020, Vikas Shah ◉

Disclosures:

At the time the article was created Vikas Shah had no recorded disclosures.

View Vikas Shah's current disclosures

Last revised:

11 Dec 2023, Yuranga Weerakkody ◉

Disclosures:

At the time the article was last revised Yuranga Weerakkody had no financial relationships to ineligible companies to disclose.

View Yuranga Weerakkody's current disclosures

Revisions:

5 times, by 4 contributors - see full revision history and disclosures

Systems:

Gastrointestinal, Urogenital, Gynaecology

Sections:

Anatomy

Synonyms:

M line (pelvic floor)
H line (pelvic floor)
H and M lines

The H and M lines are reference lines for the pelvic floor on imaging studies and help detect and grade pelvic floor prolapse on defecography studies.

The H line is drawn from the inferior margin of the pubic symphysis to the posterior aspect of the anorectal junction, and represents the diameter of the levator hiatus, and a normal value is <6 cm. Grading of hiatal enlargement during evacuation using H line dimensions is as follows:

<6 cm: normal
6-8 cm: mild
8-10 cm: moderate
>10 cm: severe

The M line is drawn perpendicularly from the posterior end of the H line to the pubococcygeal line, and represents the descent of the hiatus, and a normal value is <2 cm. Grading of hiatal descent during evacuation using M line dimensions is as follows:

<2 cm: normal
2-4 cm: mild
4-6 cm: moderate
>6 cm: severe

There is a discrepancy in the literature about the grading of pelvic floor descent with variation between the measurements used for the posterior compartment in the pubococcygeal line (PCL) system, and the M line.