68Ga-DOTATATE PET/CT: The Optimum Standardized Uptake Value (SUV) Internal Reference.

RATIONALE AND OBJECTIVES: Standardized Uptake Value (SUV) is an important semiquantitative measurement used in the clinical and research domains to assess radiopharmaceutical concentration in tumors versus normal organs, but is susceptible to many factors beyond the tumor biological environment. So, the aim of this study is to identify the optimum internal reference among organs with physiological uptake in 68Ga-DOTATATE PET/CT (DOTA PET/CT) scans. MATERIALS AND METHODS: This HIPAA-compliant, IRB-approved study with waiver of consent included retrospective imaging review of 180 consecutive patients with neuroendocrine tumors presenting for DOTA PET/CT image acquisition: Ga-68 DOTATATE dose was reported as (0.054 mCi/Kg) scans between September 2018 and May 2019. Mean value of body weight normalized SUV (SUVbw) and lean body mass normalized SUV (SUL) of liver and spleen were measured. Information about the patients and scan characteristics were collected. The paired Grambsch test was used to compare variance among the measured SUVs. Spearman's rank correlation coefficient was used to assess correlation between SUVs and potential patient- and scan-specific confounding factors. RESULTS: Variance of SUL was significantly lower than variance of SUVbw in both liver and spleen (p-value < 0.0001). Variances of liver SUVbw and SUL were significantly lower than the corresponding spleen SUVs. Liver SUL showed the lowest variance (3.69% ± 1.25%) among all measured SUVs. CONCLUSION: SUL is a more reproducible, less variable, and therefore more reliable quantitative measure in DOTA PET/CT scans, compared SUVbw. Among the available organs with physiological uptake, liver SUL is the optimum internal reference given the liver's larger size and uniform SUL values resulting in lower variability and better reproducibility.

Iatrogenic Cushing's syndrome on 18F-FDG-PET/CT: A pitfall in metabolic assessment of oncologic response.

Iatrogenic Cushing's syndrome has very well-known stigmata on physical examination but can pose a diagnostic challenge when it rarely presents radiologically. We present a classic albeit rarely encountered imaging appearance of Iatrogenic Cushing's on 18F-FDG-PET/CT, with diffuse subcutaneous white adipose proliferation and metabolic activation in a 7-year old patient one-month after starting a high dose steroid regimen for lymphoma. There was an extreme shift in the expected FDG biodistribution with dominant localization to the subcutaneous adipose tissue. This metabolic shift led to sub-threshold visceral biodistribution, rendering the scan non-diagnostic with regards to assessment of oncologic response. Aside from detailing the characteristic imaging findings of Iatrogenic Cushing's and its clinical importance, we discuss the physiologic basis of this imaging pattern and the rarer differential diagnosis to consider when this pattern of uptake is encountered on 18F-FDG-PET/CT.

Pilomatrixoma, a Rare Mimicker of Male Breast Cancer.

Pilomatrixoma or calcifying epithelioma of Malherbe is a benign skin tumor arising from the hair follicle; breast occurrence is considered a rarity. Clinically presenting as a palpable abnormality and with both benign and malignant mammographic and sonographic features, it can be easily misdiagnosed as a breast neoplasm. We report a very rare case of pilomatrixoma of the male breast in a 36-year-old male presenting with a firm, superficial nodule in the upper outer quadrant. Though the sonographic trifecta of imaging features (shape- margins-orientation/oval, circumscribed mass, parallel to the skin) is consistent with a benign lesion, a histologic diagnosis was warranted based on its most suspicious feature of internal pleomorphic calcifications. Pathologic diagnosis revealed the uncommon benign entity of pilomatrixoma in the male breast. Our patient was recommended for surgical excision based on current literature recommendations for management in most reports of pilomatrixoma. One alternative recommendation presented in a single report of pilomatrixoma in the breast supported follow-up imaging based on benign imaging characteristics.