General Reading Caveats
Reading In Context: “Oncologic Plausibility”:
As radiologists, we don’t like to think of ourselves as gamblers, but the fact remains that our ultimate responsibility of helping the patient and clinician requires us to “play the odds”.
Simply reporting every hypermetabolic focus as a “possible malignancy” is unhelpful and, frankly, unethical.
When approaching a potentially abnormal hypermetabolic focus, we must analyze it in the context of the specific cancer and its particular presentation in the patient we are evaluating, asking ourselves:
- Is this an expected site for malignancy (primary or metastatic)?
- Is there a potential non-malignant explanation for the finding?
When we have a real suspicion – based on experience and study –that a finding does not represent malignancy, we must suggest so in our reports. [Fig. 1]
Measure Size on CT, not on the PET Images:
The size of a focus of intense metabolic activity on PET images more accurately reflects the intensity of the finding than its physical dimensions. [Fig. 2]The only time size should be measured on the PET images is when the abnormality is not visible on the co-registered CT images. In such cases, we recommend clear reporting language to that effect:
“A small focus of intense uptake is noted in the left lobe of the liver, measuring roughly 1.0 cm (as measured on the PET images, as it is not seen on the non-contrast CT images).”
Never Call an Abnormality Seen Only on the First Axial Image:
The first (most superior) axial image on the PET portion of the exam often demonstrates varying degrees of noise/scatter. Unless a corresponding abnormality exists on the co-registered CT images, ignore this artifactual PET “abnormality”. [Fig. 3]
Assess the Patient’s Main Pathology Last:
Due to the tremendous volume of images created in a PET/CT exam (whole body PET images in three planes, whole body CT images in three planes, and fused images in three planes), it is very easy to focus immediately on the main pathology of the patient and overlook the tiny metastatic lesion in the left wrist.
Based on our experience (and our errors), we strongly recommend saving interpretation of the main pathology for the end of your read, first eliminating all potential distant metastatic lesions. [Fig. 4]
Beware the Ureter:
Here at PETCTMD, we do not know of a radiologist (including these authors) who has not been fooled by a small hypermetabolic focus of normal ureteral uptake. Please learn from our mistakes.
If a focus of uptake occurs anywhere along the expected course of the ureter, carefully follow the ureter on the co-registered CT images to assure yourself that the uptake does not simply represent normal ureteral uptake. This is addressed in detail, here.
