Detecting Extranodal Spread of Metastatic Diagnosis of Neck Using MRI

Extranodal spread (ENS) of metastatic disease is important to detect in cancer patients, as it indicates a greater likelihood of cancer recurrence and distant metastasis, and also affects treatment planning. Prior studies have shown similar detection rates for MRI and CT.

A recent study was conducted to determine what criteria are most predictive of extranodal spread ENS using MRI to evaluate the neck.

The Study
109 patients with a history of known metastatic nodes of the neck.

Methodology
MRIs were obtained as axial and coronal T1-weighted and T2-weighted and fat-suppressed T2-weighted spectral presaturation with inversion recovery (SPIR) images. Post-gadolinium conventional T1 images were obtained.

Nodes on MRI were carefully correlated with surgical position utilizing maps that were created by radiologists. The following criteria were used to diagnose extranodal spread:

• the “vanishing border” sign, with loss of the fat space on T1 between the node and adjacent skin, muscle, or other tissue;
• the “flare” sign, with high signal intensity around the node on fat-suppressed T2;
• the “shaggy margin” sign, with irregular or interrupted enhancement in the periphery of the node.

In addition, short-axis diameters were also evaluated.

Consensus by 2 readers was obtained and compared to the histologic results.

Results
Univariate analysis demonstrated significant correlation between all 4 criteria and the presence of ENS. Multivariate analysis demonstrated that nodal size and the flare or shaggy margin signs contributed independently to prediction of ENS, but the vanishing margin sign did not.

The flare sign demonstrated 77% sensitivity and 93% specificity and the shaggy margin sign demonstrated 65% and 99%, respectively.

Nodal short-axis size of 15 mm was 93% sensitive and 66% specific, whereas 17 mm was 78% sensitive and 84% specific.

Any combination of these did not significantly improve the diagnostic ability of the flare sign alone, which had a positive predictive value of 83% and a negative predictive value of 90%.

Conclusions
The flare sign yields the best results in determining the presence or absence of ENS. However, substantial fractions of false-negative and false-positive cases still exist.

Reviewer’s Comments
The flare and shaggy margin signs, as well as short-axis nodal diameter >16 mm, are all useful signs for detection of extranodal spread of disease on MRI. The flare sign yields the best results in analysis.

This study was useful in that it highlighted the use of the flare sign and provided statistics in terms of these criteria and the presence or absence of ENS. The following quote from the conclusions was confusing, however:

“Although combined use of these MRI criteria did not significantly improve the diagnostic ability with a single use of the flare sign, the use of these MR imaging criteria (nodal size, flare sign, and shaggy margin) would be useful for the effective diagnosis of ENS in the neck.”

I did not fully understand the intention of the authors regarding combined use of these criteria. If the flare sign is negative, but a node is large and there is a shaggy margin, would we just follow the “flare” sign?

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Author: Yaron Lebovitz, MD

Reference:
Kimura Y, Sumi M, et al. MR Imaging Criteria for the Prediction of Extranodal Spread of Metastatic Cancer in the Neck. AJNR; 2008; 29 (August): 1355-1359