What is it about?
PET or positron emission tomography is a commonly used isotope imaging to detect cancer. As a whole-body scan, PET can also identify where the cancer has spread. This is possible because cancer tissues have much higher metabolic rates compared with non-cancer tissues or organs. In children, the growing tissues in the bones can also pick up the isotope and appear as positive, albeit physiological, findings on PET. We can tell they are physiological because the uptakes are usually symmetrical between the right and the left sides. When uptakes are asymmetric, the presence of cancer is suspicious. However, our findings in this report indicate that when such asymmetry occurs in the pelvic bone (at the ischiopubic synchondrosis, the joint between the ischium and the pubis bones), it is the rule rather than exception. Therefore, such an asymmetric finding on PET should be interpreted with caution.
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Why is it important?
Accurate interpretation of the "abnormal" findings on positron emission tomography is important when children are evaluated for suspected malignant diseases.
Perspectives
There is a physiological reason why PET scan can produce an asymmetric pattern in a growing child. The junction or joint between the ischium and the pubis bones undergo changes to fuse together shortly before puberty occurs. These changes cause the joint to enlarge. However, the changes and the enlargement occur at different rates on both sides. As for the weight-bearing, non-dominant leg, the ground reaction forces prolong and exaggerate the joint changes. In 87% of children, the left leg is the non-dominant side and thus the PET changes are often seen on the left side as demonstrated in our case.
Dr Anselm C Lee
Mount Elizabeth Hospital
Read the Original
This page is a summary of: Asymmetric ischiopubic synchondrosis mimicking skeletal metastasis on positron emission tomography, Pediatric Blood & Cancer, September 2014, Wiley,
DOI: 10.1002/pbc.25247.
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