A 28-year-old woman, gravida 1 para 0, at 38 weeks gestation undergoes spontaneous vaginal delivery. After an uncomplicated delivery of the fetus and placenta, a maternal laceration is noted at the posterior vaginal opening through the vaginal mucosa and submucosa. Which of the following structures is most likely damaged in this patient?

Question

A 28-year-old woman, gravida 1 para 0, at 38 weeks gestation undergoes spontaneous vaginal delivery.  After an uncomplicated delivery of the fetus and placenta, a maternal laceration is noted at the posterior vaginal opening through the vaginal mucosa and submucosa.  Which of the following structures is most likely damaged in this patient?

Quizplus · Accepted Answer

11ec160b_3577_3a49_9249_f912b3e6a3d7_MD0001_00 The perineal body, the center of the perineum, separates the urogenital and anal triangles and anchors multiple perineal muscles. It also blends anteriorly with the superficial perineal fascia and therefore consists of muscular, fascial, and fibrous components. The structures forming and attaching to the perineal body include the: The perineum is fibrous and relatively inelastic; therefore, it commonly sustains injury with vaginal delivery (eg, laceration at the posterior aspect of the vaginal introitus). Obstetric perineal lacerations are classified based on depth and structures involved. Because perineal lacerations typically occur at the posterior vaginal midline (the weakest region), the structures that form and attach to the perineal body are most frequently injured; in particular, the bulbospongiosus muscle, which surrounds the vaginal introitus. (Choice A) The internal anal sphincter is a ring of smooth muscle surrounding the anal canal that serves to maintain high anal resting tone; injury can lead to fecal and flatal incontinence. However, because it is posterior to the perineal body (eg, bulbospongiosus muscle, transverse perineal muscle) and surrounded by the external anal sphincter, it is less likely to be damaged than the perineal body. (Choice B) The ischiocavernosus muscle arises from the ischial tuberosity and inserts into the corpus cavernosum of the clitoris. It is anterior and lateral to the perineal body and vagina; therefore, it is unlikely to sustain injury from an obstetric perineal laceration. (Choice C) The levator ani muscle (ie, iliococcygeus, pubococcygeus, puborectalis) is a wide, funnel-shaped muscle complex that forms the pelvic floor and supports the pelvic viscera. Although it can be stretched and injured by pregnancy/delivery due to increased intraabdominal pressure, the levator ani muscle is not likely to be damaged by perineal laceration because it lies superior (deep) to the perineal body. (Choice E) The sacrotuberous ligament extends from the lateral sacrum and attaches to the ischial tuberosity. It is posterior, lateral, and superior to the perineal body and would not be damaged by a perineal laceration. Educational objective: The perineal body, which is relatively inelastic, can be damaged in an obstetric perineal laceration. The structures that form and attach to the perineal body are the bulbospongiosus, superficial transverse perineal, and external anal sphincter muscles. __________ References: Connectivity of the superficial muscles of the human perineum: a diffusion tensor imaging-based global tractography study. (http://www.ncbi.nlm.nih.gov/pubmed/30552351) Anatomy, abdomen and pelvis, perineal body. (http://www.ncbi.nlm.nih.gov/pubmed/30726030)

A 28-Year-Old Woman, Gravida 1 Para 0, at 38 Weeks