Increased uptake of 99mTc MDP in mastoid process of left temporal bone and cortical thickening with ground-glass density

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

By Wei Wang and Jigang Yang, Beijing Friendship Hospital of Capital Medical University, Beijing, China
Data and images courtesy of Beijing Friendship Hospital of Capital Medical University, Beijing, China

|2021-03-04
A seven-year-old female presented with enlarged mammary glands, increased vulvar secretions, and a rapid increase in height. History indicated a normal diet and no report of ingestion of hormonal or contraceptive medications. Physical examination revealed bilateral breast enlargement with well-defined areolas. Multiple café-au-lait skin spots were visible on the vulva, hips, and back.

Laboratory examination showed normal thyroid function and cortisol levels, yet estradiol levels were elevated at 128 pmol/L (less than 115 considered normal).

The patient underwent a pelvic ultrasound that showed maturation of the uterus with enlarged follicles of the right ovary. A brain MRI was determined to be normal, and skeletal survey radiographs showed normal bone age of the metacarpal and carpal bones.

The patient subsequently underwent 99mTc MDP bone imaging with xSPECT BoneTM performed on a
Symbia IntevoTM SPECT/CT scanner.
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.
Multi-bed SPECT/CT imaging on a Symbia Intevo scanner using xSPECT Bone provides high sensitivity to help detect small foci of abnormal skeletal metabolism as well as high-quality CT for accurate evaluation of CT changes, which is critical for diagnostic accuracy in the evaluation of MAS.

Scanner: Symbia Intevo 16

PET

 

CT

Injected dose

5 mCi (185 MBq) 99mTc MDP

Tube voltage

80 kV

Post-injection delay

3 hours

Tube current

60 eff mAs

Acquisition

Planar imaging
Scan speed: 12 cm/min
xSPECT Bone tomography
Two detector acquisition,
matrix 128 x 128, 60°/stop,
30 s/stop, 30 stops/detector
Reconstruction: OSCGM

Slice collimation

1.2 mm
Scan time
• Planar imaging: 10 min
• xSPECT Bone tomography: 17 min
Slice thickness
3 mm
Reconstruction kernel
B60s

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