Читать книгу Surgical Management of Advanced Pelvic Cancer - Группа авторов - Страница 35

There are several methods for assessing cancer anatomy and resectability. Examination under anesthetic (EUA) is a common method for determining whether the cancer is adherent to adjacent structures. While palpation may help the surgeon estimate R0 resectability, radiological assessment is the main determinant of whether a cancer can be completely excised with a microscopically clear margin.

Overall, radiological assessment of cancer anatomy provides more accurate assessment of margins and the relationship to adjacent structures than EUA [24]. The radiological modalities commonly utilized include magnetic resonance imaging (MRI), computed tomography (CT), and positron‐emission tomography (PET). Advanced pelvic cancer surgery is complex and its radiological assessment is individualized according to the type of cancer, patient factors (e.g. tolerance, comorbidity, frailty, and metastatic disease), and location in the pelvis.

For low pelvic cancers with a distal margin threatening the preservation of the anal canal or anterior compartment structures (prostate/seminal vesicles in men; vagina and uterus in women) endorectal ultrasound (ERUS), when performed by experienced practitioners, can provide complementary information to assist decision‐making. The small volume of mesorectal fat between the distal rectum and anterior mesorectal margin can limit accuracy of MRI for detecting transmural extension of the tumor and anterior margin involvement by low rectal cancers.

Several retrospective studies correlating preoperative MRI staging of the circumferential resection margin (CRM) with histological CRM involvement have demonstrated decreased reliability of MRI for patients with low, anterior rectal cancer, with MRI mostly overestimating CRM involvement [25, 26]. In the authors’ experience, if MRI shows convincing involvement of anterior structures by cancer, total pelvic exenteration or posterior exenteration is recommended, to achieve R0 resection. However, where involvement of the anterior margin is equivocal, we recommend ERUS when feasible [27, 28]. In one study including 32 patients with anterior rectal cancers, MRI and ERUS had equivalent positive and negative predictive values of 66.6 and 95.6% respectively [27]. A recent retrospective study of 24 patients observed that use of ERUS as an adjunct to MRI improved diagnostic accuracy for anterior margin involvement [29]. ERUS can also provide an accurate assessment of distal cancer margin in relation to the puborectalis muscle when considering intersphincteric dissection and preservation of the anal canal. However, clinically reliable ERUS requires experience of both endoluminal ultrasound and rigid sigmoidoscopy to optimize probe position and scan interpretation [30].

PET‐CT provides complementary information on tumor function and activity [31]. PET‐CT is frequently used in complex cancer patients as a complementary test to CT and liver MRI, particularly for exclusion of metastatic disease in uncommon sites or to help troubleshoot uncertain imaging findings, for example helping distinguish tumor from scar tissue or presence of nodal involvement. PET‐CT utility is limited by poor spatial resolution, anatomical mismatch between sites of disease and displayed metabolic activity (due to patient movement or bowel peristalsis), and false positives generated by sites of inflammation or tissue healing [32].