Abstract
PurposeTo enable the evaluation of locoregional disease in the on-going RECTOPET (REctal Cancer Trial on PET/MRI/CT) study; a methodology to match mesorectal imaging findings to histopathology is presented, along with initial observations.MethodsFDG-PET/MRI examinations were performed in twenty-four consecutively included patients with rectal adenocarcinoma. In nine patients, of whom five received neoadjuvant treatment, a postoperative MRI of the surgical specimen was performed. The pathological cut-out was performed according to clinical routine with the addition of photo documentation of each slice of the surgical specimen, meticulously marking the location, size, and type of pathology of each mesorectal finding. This allowed matching individual nodal structures from preoperative MRI, via the specimen MRI, to histopathology.ResultsPreoperative MRI identified 197 mesorectal nodal structures, of which 92 (47%) could be anatomically matched to histopathology. Of the matched nodal structures identified in both MRI and histopathology, 25% were found to be malignant. These malignant structures consisted of lymph nodes (43%), tumour deposits (48%), and extramural venous invasion (9%). One hundred eleven nodal structures (55%) could not be matched anatomically. Of these, 97 (87%) were benign lymph nodes, and 14 (13%) were malignant nodal structures. Five were malignant lymph nodes, and nine were tumour deposits, all of which had a short axis diameter < 5 mm.ConclusionsWe designed a method able to anatomically match and study the characteristics of individual mesorectal nodal structures, enabling further research on the impact of each imaging modality. Initial observations suggest that small malignant nodal structures assessed as lymph nodes in MRI often comprise other forms of mesorectal tumour spread.Trial registrationClinical Trials Identifier:NCT03846882.
Highlights
Magnetic resonance imaging (MRI) of the pelvis is fundamental to the staging and restaging of patients with adenocarcinoma of the rectum [1,2,3,4]
The aim of the present study is to present a method for anatomical matching of individual mesorectal structures between preoperative MRI and histopathology as part of the on-going prospective RECTOPET (REctal Cancer Trial on positron-emission tomography (PET)/MRI/computed tomography (CT)) study
The sizes and distribution of the anatomically matched and non-matched nodal structures between staging or restaging MRI and histopathology are shown in Figs. 7 and 8, according to primary surgery (PS) or neoadjuvant treatment (NT) allocation
Summary
Magnetic resonance imaging (MRI) of the pelvis is fundamental to the staging and restaging of patients with adenocarcinoma of the rectum [1,2,3,4]. MRI is applied to assess markers, i.e. risk factors for increased risk of disease recurrence and metastatic disease, which are used to determine the optimal surgical and oncological treatment. These risk factors are the extent of the primary tumour (T-stage), spread to locoregional lymph nodes (N-stage), presence of extramural venous invasion (EMVI), and distance from the primary tumour to the mesorectal fascia (MRF). While most risk factors are readily evaluated with MRI, N-stage remains challenging to determine with high accuracy [2, 3, 5,6,7,8]. Recent studies indicate that tumour deposits (N1c) are associated with worse survival than metastatic lymph nodes when considering both types of lesions in isolation [9,10,11,12]
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