Imaging description

A three-year-old child presented with back pain and inability to stand or walk. CT and MRI demonstrated epidural masses in the midthoracic and lumbar spine causing cord compression, as well as a large right adrenal mass (Fig. 71.1a–c). Iodine-123 (123I) metaiodobenzylguanidine (MIBG) planar scintigraphy and SPECT/CT showed a large area of focal radiotracer uptake in the right adrenal gland and disseminated bone marrow involvement involving the axial and appendicular skeleton (Fig. 71.1d). Technetium-99m (99mTc) methyl diphosphonate (MDP) bone scintigraphy demonstrated destructive cortical lesions in the axial and appendicular skeleton (Fig. 71.1e). Biopsies of the adrenal mass and bone marrow confirmed metastatic neuroblastoma (NB).

Importance

NB is an embryonic tumor of the sympathetic nervous system and is the most common extracranial solid tumor in childhood. At the time of diagnosis, nearly half of the patients have distant metastases, commonly to the bone cortex and bone marrow, which confers a poor prognosis. However, involvement of the bone marrow does not always correlate with cortical bone involvement, or vice versa. The combination of 123I-MIBG scintigraphy and 99mTc-MDP bone scans gives the highest sensitivity for the evaluation of skeletal lesions. 123I-MIBG is taken into cells via the norepinephrine transporter, which allows for a sensitive and specific method for assessing disease extent in both the soft tissues and bone marrow. However, the 123I-MIBG scan alone may underestimate the extent of bone involvement. 99mTc-MDP bone scans, which better evaluate the cortical lesions, provide complementary information to 123I-MIBG scintiscans. They are based on the increased rate of calcium turnover at the site of injury, which can begin as early as 24 hours after the triggering event. During follow-up, 99mTc-MDP bone scans can remain positive for more than 6 months during the healing process whereas 123I-MIBG scans are only positive in viable, functioning lesions. Thus, MIBG is more suitable for monitoring response to therapy.