Results

It is worth noting that the cancer invasion decreased gradually in depth outward from the centre of the tumour. The level of maximum invasion therewith was located well above the distal verge of the cancer, on the average, 28.8 mm (5-50 mm) from the dentate line. In the area of distal margin of the tumour, invasion of the cancer into the rectal wall was minimum (Fig. 1). As a rule, the invasion was confined by the mucous and submucous layers of the rectal wall, which is undoubtedly favourable from the viewpoint of implementation of sphincter-saving technique.

When investigating the spread of adenocarcinoma in the circular direction, we noticed that the mean distance from the lateral margin of the cancer to the circular line of resection at a level of maximum invasion was 5 mm (range 1-10 mm). Close examination revealed no cancer cells in the circular margin of resection.

Depending on the location of the lower margin of the tumour from the dentate line, all the specimens were divided into three groups. The first group comprised 18 specimens in which the distal verge of the tumour was located 1-2 cm above the dentate line.

The second group consisted of 45 specimens, in which the caudal margin of the tumour was located within 1 cm above the dentate line. The third group comprised 8 specimens in which the tumour involved the dentate line and anal canal to within 1 cm below the anorectal junction.

In the first group, all 18 tumours were presented to adenocarcinomas in T3 stage. Most of them had histologic structure with high and good degrees of differentiation (n=17). Low differentiation was observed in one case. Examination revealed no involvement of the structures of the anal canal, the ischiorectal tissue or the perianal skin. Distal intramural spread of malignancy was not observed in this series.

In the second group, most of the tumours were attributed to adenocarcinomas of high and good degree of differentiation (n=41). A low degree of differentiation was observed in four cases. T3 stage was found in 44 cases and T4 in one case. In 36 of 45 observations the structures of anal sphincter, the ischiorectal tissue and the perianal skin were not involved in malignancy. In eight cases the involvement of the internal sphincter was observed. In this connection, the levator ani muscles, external sphincter, ischiorectal tissue and perianal skin remained intact. Interestingly, in this series, the tumour had a structure of poorly differentiated adenocarcinoma in three of eight cases.

There was only one case of poorly differentiated tumour infiltration of the levator ani muscles, the internal sphincter and the prostate. In this examination, we observed the effect of distal intramural spread of malignancy along the submucous layer and the internal sphincter over a length of 12 mm from the macroscopically determined lower margin of the

Fig. 1. Level of maximum invasion

Fig. 1. Level of maximum invasion

Tumour

Fig. 2. Distal intramural spread

Distal intramural spread

Fig. 2. Distal intramural spread tumour (Fig. 2). However, the structures of external sphincter, ischiorectal tissue and perianal skin remained intact.

Moreover, in all cases of cancer invasion into the internal sphincter, with the exception of one case with the distal intramural spread of malignancy, the lesion was not total. It was located within the upper third of internal sphincter.

In five of the eight observations in the third group, the tumours were attributed to high and well differentiated adenocarcinomas. The T3 stage was observed in six cases and the T4 in two cases. In all specimens the structures of anal canal were involved in malignancy. In six cases there was involvement of the internal sphincter within its proximal portion. The levator ani muscles, the external sphincter, the ischiorectal tissue and the perianal skin remained intact. Interestingly, in this series, the tumour had a structure of poorly differentiated adenocarcinoma in one of the six cases. In one case only, the complex lesion of the internal and portions of external sphincter were observed. The tumour possessed a low degree of differentiation. In this case, the ischiorectal tissue, subcutaneous part of external sphincter and perianal skin were not involved in malignancy.

One more examination revealed the complex lesion of the levator ani muscles, internal and external sphincter. The tumour also possessed a low degree of differentiation. However, the ischiorectal tissue and perianal skin remained intact. The data obtained in the course of investigation into involvement of the structures of the anorectal area in malignancy are presented in Fig. 3.

It must be emphasised that, in all cases, the perianal skin, subcutaneous portion of external sphincter and ischiorectal tissue remained intact. The puborec-tal muscle and levator ani muscles were not involved in malignancy in the majority of cases (97.2%). Their lesion was revealed in case of a low degree of differentiation of the tumour only. In every fifth observation, the upper third of internal sphincter was involved in malignancy. However, the incidence of its total lesion did not exceed 3%. The low degree of differentiation was observed in all cases of total lesion of internal sphincter as well as in the presence of distal intramural spread of adenocarcinoma along the submucous layer.

Thus, when the lower margin of the tumour was located within 2 cm above the dentate line, the internal sphincter was rarely involved in malignancy (9/63,14.3%). In these cases, the tumour invaded its proximal third and the spread into external sphincter (in this case, into levator ani muscles) was revealed in one specimen with a low degree of differentiation of malignancy (1.6%). Other structures of dentate area remained intact.

When the distal margin of the tumour was located below the dentate line, the internal sphincter was invaded in 100% of cases and the external sphincter in every fourth case. Such behaviour can be explained in terms of low degree of tumour differentiation. However, the ischiorectal tissue, subcutaneous portion of external sphincter and perianal skin remained intact even for this group of specimens.

The revealed behaviour of malignancy in the distal area of the rectum can be elucidated as follows: the

Fig. 3. Incidence involvement of the structures of the anorectal area

anorectal area, once being an integral anatomic-functional formation, is not the same from the viewpoint of its histogenesis. From the viewpoint of providing adequate circular margin of resection, the implementation of TME in the course of the abdominal phase of the operation allows surgeons, along with the removal of the rectum within of the visceral fascia, to take in the specimen the regional lymphatic nodes as well. The inclusion of the longitudinal muscle of anal canal in resection plan makes it possible to provide lateral clearance in the distal area of the specimen with entire or partial saving of anal sphincter.

The data obtained suggest that APR should be undoubtedly utilised when the dentate line and/or parietal fascia of the pelvis are invaded. However, the low differentiated adenocarcinomas can serve as a reason to reject the decision to save sphincter in favour of APR in cases of tumour location within 1-2 cm above dentate line as well.

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