An understanding of female pelvic and lower abdominal wall anatomy is essential for obstetrical practice. Although consistent relationships between these structures are the norm, there may be marked variation in individual women. This is especially true for major blood vessels and nerves.
Skin, Subcutaneous Layer, and Fascia
The anterior abdominal wall confines abdominal viscera, stretches to accommodate the expanding uterus, and provides surgical access to the internal reproductive organs. Thus, a comprehensive knowledge of its layered structure is required to surgically enter the peritoneal cavity.
Langer lines describe the orientation of dermal fibers within the skin. In the anterior abdominal wall, they are arranged transversely. As a result, vertical skin incisions sustain increased lateral tension and thus, in general, develop wider scars. In contrast, low transverse incisions, such as the Pfannenstiel, follow Langer lines and lead to superior cosmetic results.
The subcutaneous layer can be separated into a superficial, predominantly fatty layer—Camper fascia, and a deeper membranous layer—Scarpa fascia. Camper fascia continues onto the perineum to provide fatty substance to the mons pubis and labia majora and then to blend with the fat of the ischioanal fossa. Scarpa fascia continues inferiorly onto the perineum as Colles fascia (Perineum). As a result, perineal infection or hemorrhage superficial to Colles fascia has the ability to extend upward to involve the superficial layers of the abdominal wall.
Beneath the subcutaneous layer, the anterior abdominal wall muscles consist of the midline rectus abdominis and pyramidalis muscles as well as the external oblique, internal oblique, and transversus abdominis muscles, which extend across the entire wall (Fig. 2-1). The fibrous aponeuroses of these three latter muscles form the primary fascia of the anterior abdominal wall. These fuse in the midline at the linea alba, which normally measures 10 to 15 mm wide below the umbilicus (Beer, 2009). An abnormally wide separation may reflect diastasis recti or hernia.
Anterior abdominal wall anatomy. (From Corton, 2012, with permission.)
These three aponeuroses also invest the rectus abdominis muscle as the rectus sheath. The construction of this sheath varies above and below a boundary, termed the arcuate line (Fig. 2-2). Cephalad to this border, the aponeuroses invest the rectus abdominis bellies on both dorsal and ventral surfaces. Caudal to this line, all aponeuroses lie ventral or superficial to the rectus abdominis muscle, and only the thin transversalis fascia and peritoneum lie beneath the rectus (Loukas, 2008). This transition of rectus sheath composition can be seen best with a midline abdominal incision. Last, the paired small triangular pyramidalis muscles originate from the pubic crest, insert into the linea alba, and lie atop the rectus abdominis muscle ...