Perianal and Anal Canal Neoplasms
Philip H. Gordon, Santhat Nivatvongs, Lee E. Smith, Scott Thorn Barrows, Carla Gunn, Gregory Blew, David Ehlert, Craig Kiefer, Kim Martens in Neoplasms of the Colon, Rectum, and Anus, 2007
The anal area, although small, is rather complex due to differences in histologic features, characteristics, and lymphatic spread. Many reports of malignant neoplasms in this region use different terminologies to define the location of the malignancy. To overcome this confusion, the World Health Organization (WHO) and the American Joint Committee on Cancer (AJCC) have developed a universally accepted descriptive terminology for the histologic typing of intestinal neoplasms of the anal region (1,2). According to their terminology, “The anal canal is defined as the terminal part of the large intestine, beginning at the upper surface of the anorectal ring and passing through the pelvic floor at the anus. The lower part extends from the dentate line and downwards to the anal verge” (1). This is essentially the “surgical anal canal.” The perianal skin (the anal margin) is defined by the appearance of skin appendages (such as hairs). There exists no generally accepted definition of its outer limit (1). Some authors defined the lateral or distal extent of the perianal skin as 5 to 6 cm from the anal verge (3,4). This definition is in contrast to many series in the literature that use the dentate line as the dividing line describing the anal canal as the area above the dentate line, and the anal margin as the area below the dentate line (5–9). Numerous other reports never define the landmarks.
Anatomy
Peter Sagar, Andrew G. Hill, Charles H. Knowles, Stefan Post, Willem A. Bemelman, Patricia L. Roberts, Susan Galandiuk, John R.T. Monson, Michael R.B. Keighley, Norman S. Williams in Keighley & Williams’ Surgery of the Anus, Rectum and Colon, 2019
The anal canal is the most terminal part of the lower gastrointestinal tract and is completely extra-peritoneal. It is approximately 4 cm long, commencing above at the level where the rectum passes through the pelvic diaphragm and terminating below at the anal verge. The pelvic diaphragm is comprised of the levator ani muscles and the small coccygeus muscles, together with their investing fascia. Anteriorly, the diaphragm is incomplete to permit passage of the urethra and the urethra and vagina, in males and females, respectively. The muscular junction between the rectum and the anal canal is palpable on digital rectal examination as the anorectal ring which is formed by the union of puborectalis fibres from the two levator ani muscles, the deep portion of the external anal sphincter and the highest fibres of the internal anal sphincter (Figure 1.14).
Mechanisms of Continence and Defecation
Han C. Kuijpers in Colorectal Physiology: Fecal Incontinence, 2019
The mean length of the anal canal is 4 cm (3.7 cm in women and 4.6 cm in men).1 The anal canal is encircled by the internal and external anal sphincter muscles, forming a high-pressure zone. The internal anal sphincter is a condensation of smooth muscle fibers derived from the caudad continuation of the inner circular muscular layer of the rectum. The internal anal sphincter is normally in a state of continuous maximum contraction. Control is mediated by sympathetic innervation from the hypogastric nerves and fifth lumbar root, and parasympathetically by the first, second, and third sacral roots. Internal anal sphincter tone is enhanced by pelvic sympathetic nerve stimulation or the administration of noradrenaline;2,3 in contrast, presacral sympathetic denervation or administration of a-adrenergic antagonists causes relaxation.2,3
Patterns in ano-rectal dose maps and the risk of late toxicity after prostate IMRT
Published in Acta Oncologica, 2019
Eva Onjukka, Claudio Fiorino, Alessandro Cicchetti, Federica Palorini, Ilaria Improta, Giovanna Gagliardi, Cesare Cozzarini, Claudio Degli Esposti, Pietro Gabriele, Riccardo Valdagni, Tiziana Rancati
Treatment data, including 3D-dose distributions, were imported into VODCA (MSS Medical Software Solutions GmbH, Switzerland) for the generation of DSMs [22] for the anal canal and rectum as a single structure, and for the anal canal and the rectum separately. The anal canal was defined as the structure extending 3 cm cranially of the anal sphincter. The rectum was defined from the anal canal to the point where the structure starts turning anteriorly. DSMs were extracted from VODCA after a review of the segmentation of the OAR. The dose map of the tubular surface of the OAR was unfolded along the posterior axis and converted into a 2D-dose map. The lateral (left-right direction) extent of the map varies with the circumference of the outline of each image slice, and corresponds to a snapshot of the anatomy at the time of the acquisition of the treatment-planning CT. Therefore, the dose map was represented both with this anatomical axis and with a relative lateral axis of 200 pixels, using linear one-dimensional interpolation (see Figure 1). This latter representation will be referred to as laterally normalized DSM (referring to the geometry, not dose).
Anal cancer in Sweden 2015–2019. Implementation of guidelines, structural changes, national registry and early results
Published in Acta Oncologica, 2022
Anders Johnsson, David Norman, Eva Angenete, Nina Cavalli-Björkman, Cecilia Lagerbäck, Otilia Leon, Birgitta Lindh, Marie-Louise Lydrup, Martin P. Nilsson, Mats Perman, Calin Radu, Björn Zackrisson
As of 1st of April 2021, 912 patients had been registered in the SACR, diagnosed with anal cancer between 2015 and 2019. The median age was 68 years and 76% were females (Table 1). WHO performance status was 0–1 in 76% of cases. A majority of tumors (85%) involved the anal canal. In 11% of cases the tumor was entirely located in the anal margin. The distal rectum was involved in 25% of cases and in 3% of patients the tumor was solely located in the rectum without growth in the anal canal. Lymph node metastases (N1-3) were present in 52% of patients and 9% had distant metastases (M1) at diagnosis, most frequently in the liver followed by extrapelvic lymph nodes and lung. Positive staining for p16 in the tumor was observed in 90% of patients, 95% among women and 77% among men. The proportion of patients receiving a pretreatment stoma was 14%.
Angiogenesis inhibitors and symptomatic anal ulcers in metastatic colorectal cancer patients**
Published in Acta Oncologica, 2018
Francesca Bergamo, Sara Lonardi, Beatrice Salmaso, Carmelo Lacognata, Francesca Battaglin, Francesco Cavallin, Luca Saadeh, Sabina Murgioni, Antonino Caruso, Camillo Aliberti, Vittorina Zagonel, Carlo Castoro, Marco Scarpa
Anal fissures are linear lesions located in the distal mucosa of the anal canal beneath the dentate line and these lesions can usually be observed at a slight eversion of the anal canal. Anal ulcers are defined as oval lesions normally located near the dentate line with a diameter greater than 1 mm and at least 1 mm deep. Usually, they are not observable at external inspection of the anal canal [13]. In the general population, the pathophysiology of anal fissure is likely related to trauma from either the passage of hard stool or prolonged diarrhea. A tear in the anoderm causes spasm of the internal anal sphincter, which causes further pain, increased tearing and decreased blood supply to the anoderm. This cycle of pain, spasm and ischemia contributes to the development of a poorly healing wound that becomes a chronic fissure. Moreover, anal fissures are classified as acute or chronic: acute anal fissures typically heal with medical treatment in 4–6 weeks; instead chronic fissures persist beyond 6 weeks. 90% of anal fissures are located at the posterior midline, while the remaining 10% develop at the anterior midline, most commonly in women [13]. Multiple or lateral fissures could be indicative of one the following diseases: inflammatory bowel disease, sexually transmitted diseases (syphilis or HIV), tuberculosis, leukemia or anal canal cancer [14,15]. So far, the only medication associated with the development of anal ulcers is the vasodilatory drug used to treat angina, nicorandil [16], but no report has ever suggested an association between antiangiogenic drugs and anal ulcers.
Related Knowledge Centers
- Gastrointestinal Tract
- Ischioanal Fossa
- Sphincter
- Perineum
- Feces
- Rectum
- Pelvic Floor
- Anus
- Anal Triangle
- Lumen