Metastatic superscan on ^99mTc-methylene diphosphonate bone scintigraphy in pediatric neuroblastoma

Excessive skeletal radioisotope uptake in relation to soft tissues along with absent or faint activity in the genitourinary tract on bone scintigraphy (BS) is known as a “superscan”.[1] Common causes include prostate cancer, breast cancer, and lung cancer.[2] Hematological conditions like leukemia, lymphoma, myelofibrosis, Waldenstrom's macroglobulinemia are sometimes associated with metastatic superscan. Metabolic bone diseases such as renal osteodystrophy, Paget's disease and hyperparathyroidism are also reported as the rare causes of superscan. Occasionally superscan is seen in hyperthyroidism and fibrous dysplasia. Some of the other rare causes for metastatic superscan include urinary tract transitional cell carcinoma and nasopharyngeal carcinoma.[234] However, association of pediatric solid tumor malignancy with metastatic superscan has not been reported previously. We here describe two such cases of neuroblastoma (NB) who presented with metastatic superscan on ^99mTc-methylene diphosphonate (MDP) BS. First case was a 12-year-old male child, a known case of mediastinal NB [Figure 1a, anterior and 1b, posterior] and second was a 4-year-old male child, a known case of abdominal NB [Figure 1c, anterior and 1d, posterior] sent to our department to rule out cortical bone involvement.^99m Tc-MDP BS showed heterogeneously increased radiotracer uptake in the entire axial and appendicular skeleton in both the cases suggesting widespread skeletal metastases with cortical involvement and giving the appearance of a metastatic superscan. Though metastatic superscans on ¹²³I-Metaiodobenzylguanidine have been reported in patients of NB,[5] to our knowledge this is the first instance on ^99mTc-MDP BS. The bone scan shows uptake due to marrow edema and bone matrix irritation leading to increased osteoblastic turnover. The importance of bone scan in NB is to distinguish stage 4 from stage 4s. Stage 4s occurs in infants who have a localized tumor that does not cross the midline, with metastatic disease confined to the liver, skin, and bone marrow and with no evidence of cortical bone involvement observed.[6] Bone scan thus rules out cortical bone involvement. Superscan is often confused with normal skeletal scintigraphy. Nonvisualization of the kidneys in a skeletal scintigraphy should alert the physician for presence of a superscan in case the renal function is normal. Presence of a superscan usually indicates an advanced stage of the disease, when there has already been extensive bone marrow infiltration, followed by an osteoblastic reaction. The patient prognosis is usually poor.[2] Though extremely rare superscan can be associated with pediatric solid tumor malignancies and should be kept in mind while reporting such cases.

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Figure 1 ^99mTc-methylene diphosphonate bone scintigraphy (BS) in a 12-year-old case of mediastinal neuroblastoma (NB) (a, anterior; b, posterior) and 4-year-old case of abdominal NB (c, anterior; d, posterior) shows heterogeneously increased radiotracer uptake in the entire axial and appendicular skeleton suggesting widespread skeletal metastases with cortical involvement giving the appearance of a metastatic superscan

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