Arrangement of the anal striated musculature

Electromyography of the anal sphincter: which muscle to examine?

Electromyographic examination of the deeper external anal sphincter (EAS) muscle is far more uncomfortable than of the subcutaneous muscle, so we tested the need for its examination. We compared the findings in 85 paired examinations of ipsilateral subcutaneous and deeper EAS muscles in 67 patients with a cauda equina lesion. When the other muscle was normal, the deeper or subcutaneous muscle was pathological in 18% or 13% of pairs, respectively. In addition, the subcutaneous EAS muscle was usually more severely affected than the deeper EAS muscle. Thus, examination of the deeper EAS muscle did not increase the sensitivity of MUP analysis significantly, and did not seem clinically necessary.

Three-dimensional reconstruction of the anorectal continence organ in a 14-week-old fetus

BACKGROUND/PURPOSE

The fetal development and anatomy of the muscular structures of the anorectal continence system are unclear. To the pediatric surgeon, these structures are of clinical relevance in reconstructive surgery. The aim of this study was to investigate the fetal development of the anorectal continence organ.

METHODS

A male fetus (14 weeks postconceptionem) of 114-mm crown-rump length was sectioned serially at 18-micrometer intervals. The sections were stained, and relevant contours of the sections were transferred onto paper using a Zeiss Axioskop drawing apparatus. The drawings then were scanned and digitized.

RESULTS

Three-dimensional images were created (and animated in a video). These have permitted the demonstration of isolated anatomic structures, the disassembling and reassembling of compound structures, as well as the visualization of structures from different angles.

CONCLUSIONS

Further studies are now undertaken of older fetal stages through to birth, as well as during postnatal stages. Comparative studies in animals and animations of isolated muscles also are required to show functional capacities. Such studies may lead eventually to an improvement of contemporary surgical techniques.

Standardization of anal sphincter electromyography: uniformity of the muscle

The different parts of the external anal sphincter (EAS) are usually regarded as one muscle with common EMG characteristics. This assumption was addressed by comparing the number of continuously firing motor units (MUs) during relaxation, as well as the parameters of motor unit potentials (MUPs) and interference pattern (IP) in the subcutaneous and the deeper parts of EAS. MUPs and IPs were analyzed in 44 subjects (2008 MUPs and 3014 IPs) without uroneurological or proctological disorders, and the number of continuously active MUs in 34 of these subjects was recorded (221 positions). No significant difference was found in IP and most MUP parameters between the two parts of the EAS muscle, but the number of continuously firing MUs was lower in the deeper part. As far as MUP and IP characteristics are concerned, the whole EAS can be considered as one muscle, but some differences in patterns of activation of MUs may exist in different regions.

Anorectal motor physiology and pathophysiology

Disorders of anorectal function are complex. A clear definition of the underlying pathophysiologic process is possible only with the use of the anal physiology laboratory. A reasonable treatment plan is then possible.