Incidence and Risk Factors for Brown Adipose Tissue Uptake in PET Imaging in Pediatric Patients.

BACKGROUND: Positron emission tomography (PET) scans are used in disease diagnosis and evaluation for pediatric oncology patients. Brown adipose tissue (BAT) 18 F-fluorodeoxyglucose-PET uptake is reported in 35% to 47% of pediatric patients. Several risk factors may be associated with BAT uptake. OBJECTIVE: The aim was to determine the incidence and risk factors for BAT in pediatric patients using a consensus-based system and a novel grading scale. METHODS: A total of 285 PET scans in 154 patients were retrospectively reviewed for the presence of BAT from September 2015 through December 2016. A consensus review was done by 2 radiologists, who graded BAT on a 0 to 3 scale and assessed its impact on PET interpretation. RESULTS: The presence of moderate to severe BAT occurred in 11% of PET scans, and 6% of PETs had limited interpretation. Hodgkin lymphoma (n=53) patients had a 3.62-fold increased odds of moderate or severe BAT and a 6.59-fold increased odds of limited interpretation on PET imaging. CONCLUSION: The incidence of BAT was low but impacted radiologic interpretation when present. Further studies with a larger group of Hodgkin lymphoma patients are needed to explore the risk factors associated with moderate or severe BAT.

Equivocal end-of-therapy imaging findings do not predict a higher risk of local relapse after definitive radiotherapy in pediatric Ewing sarcoma and rhabdomyosarcoma.

BACKGROUND: Posttherapy imaging studies can provide reassurance or induce anxiety regarding risk of recurrence for patients and their families. In some cases, it is difficult to determine if imaging findings represent posttreatment changes or residual disease. Equivocal radiographic findings can occur due to therapy-related inflammation or residual, inactive soft tissue masses, but it is unknown if such findings indicate an increased likelihood of local recurrence. The aim of this study was to assess the value of initial posttherapy scans for predicting local relapse in patients with Ewing sarcoma (EWS) or rhabdomyosarcoma (RMS) who received radiotherapy (RT) for local control. These findings are critical to inform clinicians' surveillance recommendations and ability to accurately counsel patients and their families. PROCEDURE: The primary endpoint was time to local progression (LP). Patients were classified as having posttherapy scans that were "positive" (residual disease within the RT field), "negative" (no evidence of residual disease within the RT field), or "equivocal" (no determination could be made). The value of initial posttreatment scans for predicting LP was assessed using positive predictive value (PPV) and negative predictive value (NPV). RESULTS: Negative imaging findings (n = 51) had an NPV of 88%, and positive imaging findings (n = 1) had a PPV of 100%. When equivocal findings (n = 16) were categorized with negative results (i.e., positive vs. equivocal/negative), the NPV was 90%. When equivocal findings were categorized with positive results (equivocal/positive vs. negative), the PPV was 12%. CONCLUSION: Equivocal findings within the RT field on end-of-therapy imaging studies indicate no higher risk of local recurrence than negative findings. These results may contribute to appropriate surveillance schedules and accurate counseling of patients with RMS and EWS who have received RT for local control.

Neuroendocrine prostate cancer or prostatitis? An unusual false positive on gallium-68 DOTA-Tyr3-octreotate positron emission tomography/computed tomography in a patient with known metastatic neuroendocrine tumor.

The importance of gallium-68 DOTA-Tyr3-octreotate (68Ga DOTATATE) positron emission tomography/computed tomography (PET/CT) in the imaging of neuroendocrine tumors (NETs) has grown substantially over the past decade and is becoming markedly more common. We present the case of a male with known metastatic NET who underwent 68Ga DOTATATE PET/CT for restaging, incidentally revealing intense uptake of the prostate with a maximum standard uptake value of 17.4. Due to the patient's medical history, this finding was concerning for neuroendocrine prostate cancer. However, core biopsies of the prostate were negative for malignancy and positive for chronic inflammation. Chronic prostatitis is a very common condition in adult males and is often asymptomatic. Inflammatory conditions, including prostatitis, are important causes of false-positive findings on 68Ga DOTATATE PET/CT and should be considered as part of the differential diagnosis, even in an asymptomatic patient.