Saturday, May 23, 2009

Oily Fish and Enhancing Masses

This is a photograph of a herring, a small, oily fish of the genus Clupea found in the shallow, temperate waters of the North Pacific and the North Atlantic, including the Baltic Sea.

Most people are familiar with the term "red herring". In the investment world, a red herring is associated with initial public offerings (IPOs). A red herring is a preliminary registration statement that must be filed with the SEC describing a new issue of stock and the prospects of the issuing company.

Outside the financial world, a red herring is an item or event that distracts the observer from what is truly important. The origin of the term is somewhat controversial but most associate it with hunting. When herrings are cured, they turn red and acquire a distinctive smell. Hunting dogs were taught to follow a trial by following the scent of a herring that was dragged along the ground. Red herrings may also have been used to confuse the hounds in order to prolong a fox hunt or to test their ability to stay with a scent.

Occasionally, we run across red herrings in medicine as well. In this case, a 35 year-old female presented to her physician with a mass behind the elbow. She was sent for an MRI:

(A) Coronal T1-weighted and (B) T2 fatsat images reveal a T2 hyperintense mass (red arrows) corresponding to a clinically palpable abnormality.

An axial T2 fatsat image confirms the mass (red arrows) under a skin marker placed by the technologist (yellow arrow):

(A) Axial precontrast T1 fatsat and (B) postcontrast T1 fatsat images obtained immediately after IV contrast administration reveal strong enhancement associated with the lesion, which has irregular margins:

The history obtained by the MRI technologist reported no history of recent trauma. Given this, a differential of various neoplastic entities was offered, and the patient was referred to an orthopedic oncologist.

Up to this point, the patient had proceeded at a breakneck pace through the medical system. At the orthopedic oncologist, things finally slowed down. The astute orthopedic oncologist obtained a careful history, which included a possible history of a bleeding disorder. After careful consideration, he opined that this was likely a hematoma, despite the strong enhancement seen on MRI.

Over the next several weeks, the mass decreased in size, and a follow-up scan eight weeks later confirmed resolution of the hematoma:

This case illustrates many things, not the least of which is the importance of an accurate clinical history. It is also a good example of how hematomas can rarely enhance, particularly along their periphery. Cases have been described of chronically expanding hematomas which enhance, simulating a neoplasm (Skel Rad 35:1432, 2006)

Although gadolinium enhancement is often associated with neoplasms, in some cases it can be a red herring, as this case illustrates.

Vic David MD

Friday, May 8, 2009

Shoulder MR Arthrography and Butterflies

Insects often uses camouflage to hide from predators. Can you find the butterfly in this picture?

Photo by plj.johnny
Click on image to enlarge

Although arthrography (the placement of contrast within a joint) generally increases the accuracy of MRI, on occasion the contrast can camouflage important findings.

In this case, a patient with chronic shoulder pain was sent for an MR arthrogram. Here is a T1-weighted image with fat saturation:

Here is the corresponding T2-weighted image with fat saturation:

Do you see anything important?

Here are the two images next to each other:

(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation reveal a lobulated paralabral cyst (red arrows) adjacent to the anterosuperior labrum. Note how the hyperintense fluid within the joint on makes this lesion more difficult to perceive on the T2-weighted image. As expected, the paralabral cyst is hypointense on the T1-weighted image.

I have seen several cases where paralabral cysts are missed, because they blend in with the hyperintense joint fluid on T2-weighted images. This is unfortunate, as the presence of a paralabral cyst in the shoulder is highly predictive of a labral tear.

Axial image from the same patient identifies the paralabral cyst (red arrow) and the adjacent tear of the anterosuperior labrum (yellow arrow):

Thus, on MR arthrograms, be careful not to miss paralabral cysts on T2-weighted images, due to the presence of adjacent bright joint fluid.

Did you manage to find the butterfly? Here it is (yellow arrows):

Vic David MD