pelvic cancers including locally advanced primary rectal cancers extending beyond the normal anatomical planes (beyond the total mesorectal excision (TME) plane or primary rectal beyond TME (PR‐bTME)), pelvic recurrences of previously treated cancer including recurrent rectal cancer (RRC), and recurrent squamous cell cancer (SCC) of the anus with or without colorectal peritoneal metastasis (CPM) need specialist management [1, 2].
Various exenterative techniques have evolved to address the specific anatomical and surgical challenges posed by advanced pelvic cancers [3–5]. These techniques combine visceral soft‐tissue resection with bony excision to achieve a complete pathological (R0) resection of the cancer surrounded by a rim of uninvolved tissue [2]. Disease threatening or involving the sacrum can be excised utilizing either a subperiosteal approach, partial sacrectomy, or, in selected cases with superficial involvement of the anterior cortex of the proximal sacrum, high subcortical sacral resection (HiSS) [6–8]. Cancer involvement of the lateral compartment structures including the greater sciatic notch and piriformis muscle was traditionally considered unresectable. However, in recent years surgical techniques have been refined to optimize R0 resection, including lateral pelvic compartment excision using approaches from both inside and outside the true pelvis; laterally extended endopelvic resection (LEER); and extended lateral pelvic sidewall excision (ELSiE) [9–14]. Disease extending anteriorly into the retropubic space can also be excised by penile base excision with partial pubic bone resection when involved [15, 16].
The goal of exenterative surgery is achieving microscopically complete tumor clearance (≥ 1 mm microscopically clear resection margins), termed R0 resection. Five‐year survival rates of up to 65% are achievable in patients undergoing R0 resection [17–20], while survival rates after R1 or R2 resections are significantly lower [21–23]. Consequently, R0 resection is currently considered the primary determinant of surgical outcome for advanced pelvic cancer. Furthermore, for curative intent surgery, only R0 resection will confer sufficient overall patient benefit to meaningfully outweigh the risk and morbidity of attempted resection.
To help achieve R0 resection, radiological assessment of advanced pelvic cancer should first accurately delineate the cancer margins, distinguishing viable tumor from scar tissue resulting from previous surgery or (chemo)radiotherapy, and “healthy” (uninvolved) adjacent structures. The radiologist must then create and communicate a clear roadmap for resection using surgically relevant planes to ensure R0 resection while preserving uninvolved organs. Finally, radiologists must ensure accurate and timely identification of extrapelvic metastases which could influence decision‐making on whether (and when) to offer surgery. This chapter provides a more detailed review of current practice for preoperative assessment of tumor anatomy and resectability.
Cancer Anatomy and Resectability
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].
Radiological Assessment of Cancer Anatomy by MRI
T2‐weighted MRI is the reference standard for assessment of tumor anatomy and resectability. There are two main radiological approaches for interpretation and reporting.
The first is tumor categorization according to the pelvic compartments affected, which can help determine patient prognosis. Various tumor categorization systems have been proposed and are summarized in Table 3.1. The Mayo Clinic classification is based on the presence of symptoms and the number of sites of fixation of the tumor to surrounding pelvic structures [33]; the Yamada classification describes broad categories of localized, sacral, and lateral fixation [34]; and the Wanebo classification is based on the UICC TNM system distinguishing bony or ligamentous pelvic involvement from non‐bony fixation [35]. The Memorial Sloan Kettering classification distinguishes four pelvic compartments [36], while the Royal Marsden Hospital classification distinguishes seven compartments [37]. Some of these systems have attempted to prognosticate as well, although any associations with survival outcomes must be interpreted with caution, as the different institutions had different patient populations and markedly variable R0 resection rates. Moreover, prognostication based on a compartment‐based classification is inherently subject to institutional views of which cancers are resectable according to availability of expertise at that time and not necessarily considering newer surgical techniques [6, 9, 11]. The emergence and implementation of these new techniques has changed opinion on which cancers are resectable and shifted the emphasis away from relying on compartment‐based radiological assessment alone. Indeed, most compartment‐based approaches were designed and validated retrospectively, i.e. after exenterative surgery had already been performed [37].
Table 3.1 Existing classification systems for pelvic compartments.
| Group | Criteria for classification | Definitions |
|---|---|---|
| Mayo Clinic | Symptoms |
|