^99mTc MDP SPECT/CT imaging
in the evaluation of pediatric
McCune-Albright syndrome

As observed in Figures 1-5, xSPECT Bone shows hypermetabolism in the outer upper wall of the right-eye orbit, the left mastoid, body of sphenoid, the left side of C2 vertebrae, the upper ulna, the left femoral head, and the left middle tibia. CT shows bone thickening with ground-glass density, which indicates fibrous dysplasia of bone. Combined with the clinical history, the imaging findings are consistent with McCune-Albright syndrome (MAS). The remaining skeletal system appears normal with normal physiological hypermetabolism in the growing end plates of the long bones. xSPECT Bone sharply defines focal hypermetabolism that matches corresponding CT changes exactly without partial volume effects.

MAS is a rare disease that can involve multiple systems and organs, and its specific pathogenesis is not yet fully defined. Currently, MAS is primarily considered to be a rare G-protein disease, which is a congenital non-hereditary disease caused by somatic cell G-protein alpha subunit mutations. Clinically, it can affect both men and women, but the incidence rate is significantly higher in young females than in young males.¹

The clinical presentation of MAS includes three characteristics: café-au-lait skin spots, poly-fibrous dysplasia (PFD), and early on-set puberty. Diagnosis can be made if patients present with these characteristics.

Additionally, children with MAS may also be accompanied by endocrine symptoms including hyperthyroidism, Cushing syndrome, hypophosphatemia, acromegaly, hyperparathyroidism, prolactinoma, as well as cardiopulmonary disease, chronic hepatobiliary disease, gastrointestinal polyps, thymus hyperplasia, cardiac hypertrophy, and arrhythmia. In some cases, sudden death may occur.²

Skeletal abnormalities, such as PFD, commonly occur in MAS. Skeletal abnormalities in children usually occur between the ages of 3-10 and all bones can be affected. The pathological change in bone tissue is due to the replacement of normal bone tissue by fibrous connective tissue and scattered immature bone tissue. Such bone damage can be locally accompanied by liquefaction and cystic transformation or hemorrhage. Pathological fractures often occur although malignant transformation is rare.

In this particular case, X-ray and CT findings of the fibrous dysplasia in the ulna showed the lesion was located in the medullary cavity with expansive osteolytic changes, thinning of the bone cortex, and blurring of the trabecular bone structure with ground-glass changes.³ Children often present to physicians for abnormal bone development, so imaging findings are critical for the diagnosis of this disease. Comprehensive assessment of skeletal abnormalities is crucial for the diagnosis of MAS, assessing the prognosis of patients, and making treatment decisions.

Although MAS is relatively rare, it should be taken into consideration when the bone shows diffuse involvement with poor fibrous structure accompanied by café-au-lait skin spots and early-onset puberty.

The advantage of whole-body bone imaging is its ability to help show bone abnormalities in a single scan.⁴ SPECT/CT shows changes in bone density and other related morphological changes, along with abnormal skeletal metabolism corresponding to the microstructural changes. In this case of MAS, the whole-body bone imaging showed increased distribution of ^99mTc MDP on the outer upper wall of the right orbit, left temporal bone, sphenoid, left upper ulna, left femoral head, and left middle tibia. xSPECT Bone shows sharp definition of individual skeletal lesions that closely correspond to CT changes.