Tomographic ultrasound imaging of the pelvic floor in nulliparous pregnant women: limits of normality

Objectives To define normal appearance of the puborectalis muscle on tomographic ultrasound imaging in pregnant nulliparous women, establishing limits of normality. Methods This was a subanalysis of consecutive ultrasound volume datasets of 497 pregnant nulliparous women recruited in the context of two studies. All participants were carrying a singleton pregnancy at a mean gestation of 36.4 (range, 33-38) weeks. Tomographic ultrasound imaging was performed by subsequent post-processing on volumes obtained at maximal pelvic floor contraction at 2.5-mm slice intervals, from 5 mm below to 12.5 mm above the plane of minimal hiatal dimensions, producing eight slices per patient. Results Apparent abnormalities of the insertion of the puborectalis muscle were commonly seen in slices 1 and 2, but were uncommon in slice 3 (< 8%), very uncommon in slice 4 (1%) and rare elsewhere. They were not associated with bladder neck descent. Considering published minimal criteria for diagnosing an avulsion of the puborectalis muscle (slices 3 to 5 all abnormal), this diagnosis was made in three women. On reviewing those cases, one of which was rated abnormal on both sides, two were false positive as judged by the two senior authors. However, one was judged to be highly abnormal by both senior authors, with a full avulsion diagnosed on the left. Conclusions Published minimal criteria for the diagnosis of avulsion of the puborectalis muscle by tomographic pelvic floor ultrasound imaging are highly unlikely to result in a false-positive diagnosis and appear to be sufficiently robust for clinical practice. Copyright (C) 2012 ISUOG. Published by John Wiley & Sons, Ltd.