The role of the longitudinal muscle in the anal sphincter complex

Abstract

Intersphincteric resection (ISR) enables radical sphincter-preserving surgery in a subset of low rectal tumors impinging on the anal sphincter complex (ASC). Excellent anatomical knowledge is essential for optimal ISR. This study describes the role of the longitudinal muscle (LM) in the ASC and implications for ISR and other low rectal and anal pathologies. Six human adult en bloc cadaveric specimens (three males, three females) were obtained from the University of Leeds GIFT Research Tissue Programme. Paraffin-embedded mega blocks containing the ASC were produced and serially sectioned at 250 μm intervals. Whole mount microscopic sections were histologically stained and digitally scanned. The intersphincteric plane was shown to be potentially very variable. In some places adipose tissue is located between the external anal sphincter (EAS) and internal anal sphincter (IAS), whereas in others the LM interdigitates to obliterate the plane. Elsewhere the LM is (partly) absent with the intersphincteric plane lying on the IAS. The LM gave rise to the formation of the submucosae and corrugator ani muscles by penetrating the IAS and EAS. In four of six specimens, striated muscle fibers from the EAS curled around the distal IAS reaching the anal submucosa. The ASC formed a complex structure, varying between individuals with an inconstant LM affecting the potential location of the intersphincteric plane as well as a high degree of intermingling striated and smooth muscle fibers potentially further disrupting the plane. The complexity of identifying the correct pathological staging of low rectal cancer is also demonstrated. Clin. Anat. 33:567-577, 2020.

Anus-Preserving Surgery in Advanced Low-Lying Rectal Cancer: A Perspective on Oncological Safety of Intersphincteric Resection

“…The smooth muscles cells of the LM have a complex spatial distribution [23]. Some fibers detach and run posteriorly to cover the skeletal muscle fibers of the levator ani muscle (LAM); these form the hiatal ligament (HL) [24].…”

“…The robotic platform with its technical advantages could improve TILME completeness rates, however further studies are needed. Moreover, the concept of TILME completeness has to be carefully considered along with the anatomical features of the LM (which is variable in thickness) and the presence of adjacent fat separating the LM from the EAS in the ISP [23].…”

Low muscle volume of the anal sphincter complex: A novel prognostic factor in children with anorectal malformations?

“…Anorectal malformations (ARMs) are the most common congenital intestinal malformations with a prevalence of 1 in 5000 live births [1]. The anal canal, the anal sphincter complex (ASC) [2] and the rectum are the affected anatomical structures, with a high incidence of associated sacral and spinal cord anomalies. The Posterior Sagittal Anorectoplasty (PSARP), introduced in 1982 by…”