Bimodal distribution of the blood supply to lower abdominal fat: histological study of the microcirculation of the lower abdominal wall.

Fat necrosis is a common postoperative complication in transverse rectus abdominis muscle flap breast reconstruction. A histological quantification of the blood supply to the lower abdominal fat was undertaken to define this problem further. One hundred eighty sections, 1.5 cm(2) in size, were studied from one half of the lower abdomen in 10 fresh cadavers. These represent three different depths of fat (superficial, middle, deep) and six different anatomic areas (upper, middle, and lower sectors of the medial and lateral parts of the hemiabdomen). The average diameter, number of blood vessels, and the total vascular area were measured in each section. The average diameter of the blood vessels was greater in the superficial compared with the mid fat layer (p = 0.02). The total vascular area was greater in the deep compared with the mid fat layer (p = 0.01) and the superficial fat layer (p = 0.05). The number of blood vessels was also significantly higher in the deep fat layer compared with the mid fat layer (p = 0.001) and the superficial fat layer (p = 0.01). The lower medial area of the lower anterior abdominal wall contained the largest number and average diameter of blood vessels whereas the mid lateral area contained the smallest number and average diameter; however, this did not reach significance (p = 0.1 and 0.2). The results of this study are in keeping with the bimodal vascular supply to the subcutaneous fat of the anterior abdominal wall. The deep and the superficial fat layers are supplied more richly with vessels with a larger diameter whereas the intermediate fat layer is supplied from the terminal branches of these vessels.