Carnival Mask Sign on Bone Scan of Craniofacial Metastasis of Neuroblastoma.

A craniofacial mass may cause the first clinical symptoms of malignancy. In pediatric patients, neuroblastoma, Langerhans cell histiocytosis (LCH), and acute lymphoblastic leukemia (ALL) are the most common diseases initially manifesting with bone lesions, and bone scintigraphy is a useful modality to evaluate them. The purpose of this pictorial essay was to show the scintigraphy findings of the craniofacial bones in three patients, with neuroblastoma, ALL, and LCH, and to provide a useful scintigraphic sign to differentiate these diseases. In the bone scintigraphy of neuroblastoma with craniofacial bone metastases, strong tracer uptake was evident, resembling a carnival mask. In contrast, in the two cases with LCH and ALL involving the craniofacial bones, the tracer uptake was lower than in neuroblastoma and with different distributions. Bone metastases of neuroblastoma usually occur in the periorbital craniofacial bones, and these metastases may be locally aggressive, destroying the bones; which show stronger uptake than other cranial bones. LCH is associated with varying degrees of disease activity, and its bone imaging findings differ based on its activity. Therefore, these lesions present low uptake in bone scintigraphy, showing as "cold spots". Therefore, LCH scintigraphy of the craniofacial bones does not resemble a carnival mask. The bone marrow infiltration by leukemic cells usually shows as diffuse bone marrow. Therefore, in bone scintigraphy of leukemia, the tracer uptake in the periorbital craniofacial bones is similar to other cranial bones, not presenting as a carnival mask. In conclusion, bone scintigraphy to evaluate malignant craniofacial lesions could provide useful differential diagnostic information.