Bone lesions on baseline staging rectal MRI: prevalence and significance in patients with rectal adenocarcinoma

Abstract

A T1 sequence on routine baseline staging rectal magnetic resonance imaging (MRI) is thought to help detect bone lesions. Our primary aim was to evaluate the incidence of bone lesions encountered on baseline staging rectal MRI, particularly the prevalence of bone metastases. This retrospective study included patients with rectal adenocarcinoma who underwent baseline rectal MRI at our institution between January 2010 and December 2017. The MRI report was reviewed for presence of bone lesions. When found, lesion type, presence of axial T1 non-fat-suppressed sequence, primary tumor T-stage, and presence of other organ metastases were recorded. In the absence of bone biopsy, the reference standard was follow-up imaging via computed tomography (CT), MRI, and/or positron emission tomography/CT (PET/CT) ≥ 1 year after the baseline MRI. The Wilcoxon rank-sum test and Fisher's exact test were used to compare clinicopathologic data of patients with malignant or benign bone lesions. A total of 1197 patients were included. 62/1197 patients (mean age 56.8 years (SD: 13.8), with 39 men) had bone lesions on baseline imaging, with 6 being bone metastases (0.5%, 95% CI 0.2%-1.1%). Of the 6 patients with bone metastases, 5/6 had other metastases (i.e., liver, lung) at baseline. Bone metastases on baseline rectal MRI performed for rectal adenocarcinoma are extremely rare. Furthermore, bone metastases without other organ (i.e., liver, lung) involvement is extremely rare.

Keywords: Bone neoplasm; Magnetic resonance imaging; Rectal neoplasm.

Fig. 1

Flowchart of patient inclusion

Fig. 2

Benign bone lesion at baseline in a 50-year-old woman presenting with newly diagnosed rectal cancer. Bone island in the left femoral head (arrow) on (A) axial T2 magnetic resonance imaging (MRI) and (B) corresponding CT image from staging CT CAP. A bone island is a small focus of dense (cortical) bone within the medullary space and hence is of very low signal in all MRI sequences including axial T2 MRI

Fig. 3

Right femoral head metastasis in a 52-year-old man with newly diagnosed rectal cancer. (A) Hypointense lesion on non-contrast axial T1 magnetic resonance imaging (MRI), with corresponding intermediate signal on axial T2 (B), restricted diffusion on diffusion-weighted imaging (DWI), (D) and low apparent diffusion coefficient (ADC) signal.

Fig. 4

58-year-old man with mucinous rectal tumor seen on Axial T2 magnetic resonance imaging (MRI) (A, star) with right ilium metastasis (A, arrow) in addition to L4 vertebral body metastasis (B, arrow). Axial images from baseline contrast-enhanced computed tomography (CT) show liver (C, arrow) and lung (D, arrow) metastases.

Fig. 5

Femoral head metastasis in a 35-year-old woman with newly diagnosed rectal adenocarcinoma. Metastasis is hypointense on axial T2 magnetic resonance imaging (MRI) (A), restricts diffusion on diffusion-weighted imaging (DWI) (B), and demonstrates low signal on apparent diffusion coefficient (ADC) (C), with fluorodeoxyglucose (FDG) avidity on positron emission tomography (PET)/computed tomography (CT) (D). Other organ metastases were present at PET-CT; for example, maximum intensity projection (MIP), non-contrast CT, and fused axial images show liver (E–G, arrow), lung (H–J, arrow), and pleural (H–J, arrowhead) metastases.

Fig. 6

In this study, the only patient who had bone metastasis (right inferior pubic ramus metastasis) without other visceral metastasis was a 46-year-old woman with newly diagnosed T3 rectal cancer. (A) Markedly hypointense lesion on axial T2 magnetic resonance imaging (MRI), with associated pathologic fracture and small extraosseous component (arrow). Also, there were bilateral sacral metastases (B, arrows) on axial T2 MRI.