Case of the week 5 part 2

The radiologist interpreted this study as "acute appendicitis"

In the first image (top left), we see the classic findings of acute appendicitis. The appendix is dilated with wall thickening, enhancement, and periappendiceal inflammatory changes.

However, we can appreciate a significant amount of enhancing soft tissue (red arrows) at the base of the appendix involving the cecum on the top right and bottom left images. On the coronal image, there is shouldering of the soft tissue involving the cecum. Pathology after appendectomy demonstrated adenocarcinoma.

It is best to raise this possibility prior to surgery. Once you identify a mass that may represent cancer, always take the next step and look very carefully evidence of spread or metastatic disease.

Where would you look for evidence of spread?

‍Here are the places I would look:

• Peritoneal surface: I look for discrete soft tissue nodules (not stranding or fluid), which are the most specific finding of peritoneal disease. The common locations are the dependent surface of the peritoneum in the abdomen and pelvis, paracolic gutters, along the sigmoid and ileal mesenteries, liver dome and perihepatic space, Morrison's pouch, omentum, and hepatic ligaments. Your search should include both axial and coronal planes - the coronal plane is particularly helpful for nodules along the bladder dome, which can be invisible on standard 5mm axial images, and peritoneum along the sides of the peritoneal cavity.
• Liver: it's typically small metastases that are missed, so I go back and thoroughly search the liver. Small metastases are often more conspicuous on thin section images.
• Bones: same principle as liver, it's typically small metastases that are missed. I carefully look at all the vertebral bodies; then the pedicles, lamina, and transverse processes; and finally the sagittal images. Common locations for missed osseous metastases are the pedicle, ischial tuberosity, anterior pelvis at the junction of the superior pubic ramus and acetabulum, and sacrum. There was an attending where I did residency who would all of a sudden slow down while looking at the bones, particularly the sacrum and vertebral bodies. Now I understand why - he was looking for subtle bone metastases.

Let's say you were scrolling through the pelvis on bone windows and saw the lesion in the left posterior iliac bone shown below. Would you call that a metastasis?

Helpful tip

If you find a lytic lesion on CT, use soft tissue windows. If the lesion contains either fat or fluid, it is benign and not a metastasis. If it looks like soft tissue (plenty of muscle adjacent to the spine to compare to), then it is suspicious for metastasis. On the image below, the lesion clearly contains fat when compared to the subcutaneous fat.

This is reliable if the patient has not already undergone therapy, which can cause the soft tissue to regress and measure fat or fluid. In this case, it is best to go back to the early imaging to determine if a bone lesion was originally a metastasis or present and unchanged since before treatment.