A pictorial overview of pubovisceral muscle avulsions on pelvic floor magnetic resonance imaging

Abstract

ObjectivesDespite extensive research aimed at clarifying (failing) pelvic organ support, the complete aetiology of pelvic organ prolapse (POP) is still not fully understood. During vaginal delivery, the pelvic floor can be irreversibly traumatised, resulting in pubovisceral muscle avulsions. The aetiology of these avulsions is discussed in this pictorial overview. Normal female pelvic floor anatomy is described and variations are exemplified using magnetic resonance (MR) images. The clinical relevance of detecting pubovisceral muscle avulsions is specified.MethodsT2-weighted MR imaging has multiplanar capabilities with high diagnostic accuracy allowing for detailed visualisation of the pelvic floor. Together with the use of a three-dimensional (3D) post-processing program, the presence and severity of pubovisceral muscle avulsions can be quantified.ResultsPelvic floor MR imaging is a non-invasive method that enables adequate identification of pubovisceral muscle avulsions which are known risk factors for the development of POP. They can be scored with good to excellent inter- and intra-observer reliability.ConclusionsRadiologists and urogynaecology subspecialists should be familiar with MR imaging findings of pubovisceral muscle avulsions as this birth-related trauma is observed in over 36 % of vaginally parous women.Teaching Points• Pelvic organ prolapse (POP) is a growing problem for both patients and for our healthcare system• Pubovisceral muscle avulsions are known risk factors for pelvic organ prolapse (POP)• T2-weighted MR imaging visualises pubovisceral muscle avulsions adequately• Pubovisceral muscle avulsions are scored with good to excellent inter- and intra-observer reliability

Is obstetric anal sphincter injury a risk factor for levator ani muscle avulsion in vaginal delivery?

“…One of these studies, however, was retrospective and was conducted in women with pelvic floor dysfunction many years after they had given birth and the other was not designed specifically to assess the relationship between OASI and LAM avulsion. It is therefore difficult to decide whether this link was causal or associative in these studies because the two complications share some risk factors.…”

“…The sample size was determined considering previously published data that found an incidence of LAM avulsion of about 30% for all vaginal deliveries (10–40% depending on the type of vaginal delivery) and that found that OASI was a risk factor for LAM avulsion. For this calculation, we estimated a difference of 30% in the incidence of LAM avulsion between groups, a 10% rate of missing data, a 5% rate of Type 1 error (alpha = 0.005) and statistical power of 80% (beta = 0.20).…”

“…Shek and Dietz defined the tearing, or avulsion, of LAM as a defect or discontinuity of muscle fibers from the lateral pelvic wall near to their insertion. According to the literature, both magnetic resonance imaging and three‐ and four‐dimensional (3D/4D) ultrasound studies have found that the incidence of LAM avulsion varies between 15% and 36% in first vaginal deliveries. The incidence differs significantly depending on the type of vaginal delivery.…”

“…Furthermore, OASI and LAM avulsion share common risk factors, such as instrumental vaginal delivery, fetal macrosomia and a prolonged second stage of labor. As some of these factors are interrelated, it is difficult to assess their isolated effects.…”

3 T MRI-based measurements for the integrity of the female pelvic floor in 25 healthy nulliparous women

“…MRI makes it possible to obtain high‐resolution images of pelvic floor structures in two or three dimensions by using a 1.5 T or even better a 3 T scanner. This produces in particular higher soft tissue contrast and better resolution …”