Microscopic spread of low rectal cancer in regions of mesorectum: Pathologic assessment with whole-mount sections

Abstract

AIM:To assess the microscopic spread of low rectal cancer in mesorectum regions to provide pathological evidence for the necessity of total mesorectal excision (TME). METHODS:A total of 62 patients with low rectal cancer underwent low anterior resection and TME, surgical specimens were sliced transversely on the serial embedded blocks at 2.5 mm interval, and stained with hematoxylin and eosin (HE). The mesorectum on whole-mount sections was divided into three regions: outer region of mesorectum (ORM), middle region of mesorectum (MRM) and inner region of mesorectum (IRM). Microscopic metastatic foci were investigated microscopically on the sections for the metastatic mesorectal regions, frequency, types, involvement of lymphatic vessels and correlation with the original rectal cancer. RESULTS:Microscopic spread of the tumor in mesorectum and ORM was observed in 38.7% (24/62) and 25.8% (16/62) of the patients, respectively. Circumferential resection margin (CRM) with involvement of microscopic metastatic foci occurred in 6.5% (4/62) of the patients, and distal mesorectum (DMR) involved was 6.5% (4/62) with the spread extent within 3 cm of low board of the main lesions. Most (20/24) of the patients with microscopic metastasis in mesorectum were in Dukes C stage. CONCLUSION:Results of the present study support that complete excision of the mesorectum without destruction of the ORM is essential for surgical management of low rectal cancer, an optimal DMR clearance resection margin should be no less than 4 cm, further pathologic assessment of the regions in extramesorectum in the pelvis is needed.

Role of Total Mesorectal Excision and of Circumferential Resection Margin in Local Recurrence and Survival of Patients with Rectal Carcinoma

“…5 mm in diameter are more often involved by the tumor than bigger ones. Such findings pinpoint the importance of TME [24][25][26] . The pathologist must differentiate the peritonealized from non-peritonealized surfaces of the resection.…”

Prognostic value of tumour regression grading and depth of neoplastic infiltration within the perirectal fat after combined neoadjuvant chemo-radiotherapy and surgery for rectal cancer

“…Involvement of the lateral resection margins correlates with a bad prognosis and is a prognostic factor for local recurrence. 12 42 43 These results led us to consider tumour regression grading and the depth of neoplastic infiltration within the perirectal fat as new important prognostic factors for rectal cancer that should be evaluated, after combined neoadjuvant CRT and surgery, in order to plan better therapeutic strategies based on a quantitative evaluation of the response to neoadjuvant treatment and the extent of tumour involvement.…”

“…[11][12][13][14] The technique of total mesorectal excision (TME) places great importance on the anterior and posterior planes of resection, but little information is available about the lateral resection margins, which are known to be important determinants of loco-regional recurrence. 12 13 15 16 Surgery for rectal cancer has almost gone full circle. 12 13 17 First there was a 5 cm rule, which was reduced to 2 cm because it was shown that intramural spread was confined within this border except in the most advanced disease.…”

“…12 13 15 16 Surgery for rectal cancer has almost gone full circle. 12 13 17 First there was a 5 cm rule, which was reduced to 2 cm because it was shown that intramural spread was confined within this border except in the most advanced disease. 18 Currently, in order to reduce the high morbidity of TME (16-17% leak rate), 19 20 it has been suggested that a modified form of TMEsubtotal mesorectal excision (SME) (mesorectal excision limited to 5 cm in a caudal direction)-be applied to all but the very lowest tumours, and that the 5 cm rule be reintroduced for all other rectal resections, but again there is no indication of the extent of the lateral resection margins.…”

Clinical patterns of metastasis

“…The presence of nodal metastasis in the mesorectum distal to the primary tumor occurs in up to 20% of patients. Most of these metastases are located within 2 cm from the lower margin of the primary tumor; nodal metastases beyond 4 cm are exceptional [81][82][83].…”