Evolution of imaging in rectal cancer: multimodality imaging with MDCT, MRI, and PET

Abstract

Magnetic resonance imaging (MRI), multidetector computed tomography (MDCT), and positron emission tomography (PET) are complementary imaging modalities in the preoperative staging of patients with rectal cancer, and each offers their own individual strengths and weaknesses. MRI is the best available radiologic modality for the local staging of rectal cancers, and can play an important role in accurately distinguishing which patients should receive preoperative chemoradiation prior to total mesorectal excision. Alternatively, both MDCT and PET are considered primary modalities when performing preoperative distant staging, but are limited in their ability to locally stage rectal malignancies. This review details the role of each of these three modalities in rectal cancer staging, and how the three imaging modalities can be used in conjunction.

Keywords: Rectal cancer; computed tomography (CT); magnetic resonance imaging (MRI); positron emission tomography (PET); staging.

Figures

Figure 1

Normal appearance of the rectum on T2 weighted images. In both images, there is a clearly defined, T2 hypointense line (arrow) around the margins of the rectum, representing the intact muscularis propria.

Figure 2

Example of a T2N0 rectal cancer. Coronal (A) T2 weighted image demonstrates a small polyploid mass (arrow) arising from the wall of the rectum. Importantly, the overlying hypointense line demarcating the muscularis propria remains intact, suggesting this is not a T3 lesion. Axial post-gadolinium image (B) nicely demarcates the mass (arrow), although evaluating extension through the muscularis is not possible on this sequence.

Figure 3

Axial high-resolution T2 weighted image (A) demonstrates circumferential thickening (white arrow) around the entirety of the rectum, in keeping with the patient’s malignancy. In this case, the T2 hypointense muscularis is absent underlying the mass, suggesting this represents a T3 malignancy. Red arrow illustrates the intact mesorectal fascia or circumferential resection margin (CRM). Axial post-gadolinium axial image (B) demonstrates a heterogeneously enhancing malignant lymph node (arrow) in the 7 o’clock position.

Figure 4

Axial (A) and coronal (B) T2 weighted images demonstrate a polyploid mass (arrow) arising from the right lateral aspect of the rectum, with complete loss of the underlying T2 hypointense muscularis (best visualized on the coronal image), in keeping with a T3 lesion. The mass (arrow) (C) demonstrates avid enhancement on the post-gadolinium image.

Figure 5

Axial (A,B) and coronal (C) T2 weighted images demonstrate a rectal mass (white arrows) extending through the rectal wall at the 3 o’clock position into the mesorectal fat. In this case, the mass involves the CRM at this position (red arrow).

Figure 6

T4 low rectal cancer (arrows) with involvement of both the internal and external sphincters illustrated on coronal (A) and sagittal (B) T2 weighted images.

Figure 7

Rectal cancer on MDCT. Axial (A) contrast-enhanced and axial volume rendered (B) images demonstrate severe circumferential wall thickening of the rectum, with neovascularity nicely illustrated on the volume rendered 3-D image. While there is stranding and edema in the mesorectal fat, it is not possible to distinguish tumor invasion into the mesorectum from edema and inflammation. MDCT, multidetector computed tomography.

Figure 8

T4 rectal cancer on MDCT. In this case, a high rectal cancer (arrow in A) directly invades the bladder, resulting in severe left-sided hydronephrosis (arrow in B). The loss of fat plane between the bladder and rectum, as well as an appearance suggesting direct invasion, allow the diagnosis of a T4 tumor. MDCT, multidetector computed tomography.

Figure 9

T4 rectal cancer with destruction of the sacrum on MDCT. A large bulky mass directly invades, and destroys, the adjacent sacrum. MDCT, multidetector computed tomography.

Figure 10

Typical MDCT appearance of colon cancer metastases to the liver. Axial contrast-enhanced MDCT image demonstrates small, ill-defined hypodense lesions (arrow) in the right hepatic lobe. MDCT, multidetector computed tomography.

Figure 11

Axial non-contrast, non-diagnostic CT image (A) acquired as part of a PET-CT examination demonstrates severe mass-like thickening (arrow) of the rectum, corresponding to the patient’s known rectal cancer. PET image (B) demonstrates marked FDG uptake associated with the mass (arrow). Notably, the spatial resolution of PET does not allow local T staging of the lesion.

Figure 12

Axial non-contrast, non-diagnostic CT image (A) demonstrates mass-like thickening (arrow) of the rectum, corresponding to the patient’s known rectal cancer. PET image (B) at the same level demonstrates marked FDG uptake associated with the mass. PET image (C) though the liver demonstrates an occult metastasis (arrow), which was not identifiable on the patient’s formal contrast-enhanced MDCT. MDCT, multidetector computed tomography.