Secondary Hyperparathyroidism With “Superscan-Like” Hypermetabolic FDG PET/CT Pattern

Abstract

A 26-year-old man with chronic terminal renal insufficiency under dialysis was referred in our institution for a checkup before kidney transplantation to ensure the absence of malignant neoplasm. The patient had a biological secondary hyperparathyroidism with highly elevated serum parathormon, and treatment with parathyroid surgery was planned before the kidney transplant. Whole-body FDG PET/CT showed no apparent malignant neoplasm, but increased metabolism of the 4 parathyroid gland and the other pitfalls of advanced secondary hyperparathyroidism on chronic renal insufficiency: pseudotumoral calcification in soft tissues, diffuse hypermetabolic bone dystrophy, and osteolytic lesion of pelvic and peripheral skeleton corresponding to brown tumors.

Clinical pearls: Etiologies of superscan appearance on Fluorine-18-Fludeoxyglucose positron emission tomography-computed tomography

“…found that CSF-mediated diffuse marrow activation was indistinguishable from metastasis on 18-F-FDG PET/CT imaging for up to 4 days after the last administration of growth factors;[ 26 ] however, we were unable to find any report of diffuse marrow activation sequestering enough radiotracer to cause a superscan appearance on PET/CT. Primary[ 30 ] and secondary[ 14 ] hyperparathyroidism have also been reported as mimicking diffuse skeletal metastasis on 18 F-FDG PET/CT, and due to the accompanying renal failure, the diffuse skeletal activity with diminished renal excretion caused by secondary hyperparathyroidism is particularly reminiscent of the classically described skeletal superscan, and correlation with renal function laboratories may aid in avoiding diagnostic pitfalls.…”

“…A review of the literature found 17 reports in which superscans or superscan-like images were obtained on 18-F-FDG PET/CT[ 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ] [ Table 1 ]. Nine papers reported skeletal superscans,[ 3 7 8 10 14 15 16 17 18 ] seven reported hepatic superscans,[ 2 4 5 9 11 12 13 ] and one made reference to a superscan pattern in both the liver and skeleton. [ 6 ] Some authors used the term “superscan” to refer to images with intense and homogeneous skeletal or hepatic activity without a notable decrease in the normal activity usually seen in kidneys, heart, or brain.…”

“…When interpreting skeletal scintigraphy, the term “superscan” refers to a characteristic pattern consisting of symmetrically intense and diffuse radiotracer uptake in the skeleton with absent or diminished visualization of the genitourinary system and soft tissues;[ 1 ] the term has also been employed to describe a characteristic appearance on fluorine-18-fludeoxyglucose positron emission tomography-computed tomography (18-F-FDG PET/CT) imaging. [ 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ]…”

“…By analogy, superscan patterns have also been described in 18-F-FDG PET/CT scanning. [ 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ] This usage of the term “superscan” implies sequestration of radiopharmaceutical in an organ or organ system with loss or reduction in the amount of activity detected in those organs normally associated with significant physiologic uptake of 18-F-FDG such as the kidneys, brain, or myocardium. As in skeletal scintigraphy, “superscan” has been used to refer to those 18-F-FDG PET/CT scans in which diffuse and intense activity throughout the skeleton is accompanied by reduced visualization of the usual physiologic activity, especially that of the kidneys [ Figure 2 ].…”

“…Most reported superscans on 18-F-FDG PET imaging involve malignancy. [ 2 3 4 5 6 7 8 10 11 12 13 14 15 16 17 18 ] The hypercellularity and hypermetabolism required to prevent the visualization of physiologic background activities usually implies a heavy tumor burden. As such, it is important that a distinction be made between 18-F-FDG PET/CT superscans (for which few benign etiologies have been reported) and 18-F-FDG PET/CT scans which merely display very prominent avidity of a single organ or organ system without a superscan appearance (for which there are many benign causes).…”