Accuracy of clinical diagnosis of anal sphincter defect: clinical evaluation versus 3D-transperineal ultrasound.

Background: Obstetric anal sphincter injuries (OASIS) are common and an important factor in the etiology of anal incontinence. The objective of this study was to evaluate, classify and compare the agreement of clinically diagnosed third-degree sphincter tears with 3D-transperineal ultrasound (3D-TPUS) realized within 3-7 days post-delivery.

Methods: This is a retrospective observational study were 119 patients with third-degree obstetric anal sphincter tears were diagnosed and treated, 85 of those underwent a 3D-TPUS examination 3-7 days postpartum. We compared the proportion of third-degree perineal tears, classified with the clinical examination as grade 3a+b and grade 3c, with the 3D-TPUS.

Results: In 16 patients with clinically diagnosed third-degree perineal tears grade a and b, the ultrasound examination confirmed the lesion of the external anal sphincter (EAS) muscle, but in nine patients (56% of the cases) we found a lesion of the internal anal sphincter (IAS) muscle, missed by clinical examination. In the remaining 69 patients with the third-degree perineal tears grade c, the ultrasound examination confirmed both lesions (EAS and IAS muscles) in 56 women, but in 13 patients (19% of the cases) defects of the IAS muscle could not be confirmed by the ultrasound.

Conclusions: There was moderate agreement regarding diagnosis of grade 3a+b and grade c perineal tears between ultrasound and clinical examination, so a combined use of clinical and ultrasound knowledge can improve the possibility to find a gold standard in the diagnosis of OASIS.