Radiation Therapy-Induced Phrenic Neuropathy Mimicking Metastasis to the Diaphragmatic Crus on 18F-FDG PET/CT

Abstract

Benign unilateral uptake in the diaphragmatic crus is a relatively uncommon finding on 18 F-FDG PET/CT that can mimic the appearance of malignancy in patients with known cancer, as illustrated in this patient with neuroendocrine carcinoma. It is important for the PET interpreter to recognize this finding and attribute it to benign uptake based on the patient's history and symptoms at the time of the scan. Correlation with the findings of other available imaging modalities is also important to characterize focal uptake in unusual locations.

18F-Fluorodeoxyglucose Uptake in Bilateral Diaphragmatic Crura: A Relatively Uncommon Benign Variant Noted in a Treated Case of Extraosseous Paraspinal Ewing's Sarcoma

“…Albeit our patient underwent RT for Ewing's sarcoma of the paraspinal region, our patient was clinically asymptomatic at the time of 18 F-FDG scan and never had any breathing difficulties till 3 months post scan as opposed to scans elaborated by Jolepalem et al, 6 wherein benign unilateral uptake in the diaphragmatic crus was described. In case of unilateral diaphragmatic crus uptake, when the uptake is contralateral to the paralyzed hemidiaphragm, the explanation is a compensatory increase in the work of the functioning side, while for uptake on the ipsilateral side, phrenic nerve neuropathy is implicated.…”

“…In case of unilateral diaphragmatic crus uptake, when the uptake is contralateral to the paralyzed hemidiaphragm, the explanation is a compensatory increase in the work of the functioning side, while for uptake on the ipsilateral side, phrenic nerve neuropathy is implicated. 6 In the presented case, there were no such findings that would point toward hemidiaphragmatic paralysis. The only incidental finding in our case was increased tracer uptake in the vocal cords.…”

“…One of the case reports showed that the patient developed right hemidiaphragm paralysis after demonstrating right-sided unilateral crus of the diaphragm 18 F-FDG uptake, sometime after RT to neuroendocrine carcinoma of the right lung. 6 Such similar incidences of diaphragmatic paralysis have been noted after RT. [7][8][9] A known cause of 18 F-FDG uptake in muscle has been voluntary muscle activation such as exercise, labored breathing, muscle spasms, etc.…”

“…10 Similarly, there have been a reported incidence of unilateral crural uptake on 18 F-FDG PET due to increased breathing, which was hypothesized due to increased work of breathing of the right lung secondary to restricted motion of the left hemidiaphragm due to metastatic pleural disease of the left side. 11 Albeit our patient underwent RT for Ewing's sarcoma of the paraspinal region, our patient was clinically asymptomatic at the time of 18 F-FDG scan and never had any breathing difficulties till 3 months post scan as opposed to scans elaborated by Jolepalem et al, 6 wherein benign unilateral uptake in the diaphragmatic crus was described. In case of unilateral diaphragmatic crus uptake, when the uptake is contralateral to the paralyzed hemidiaphragm, the explanation is a compensatory increase in the work of the functioning side, while for uptake on the ipsilateral side, phrenic nerve neuropathy is implicated.…”

“…In case of unilateral diaphragmatic crus uptake, when the uptake is contralateral to the paralyzed hemidiaphragm, the explanation is a compensatory increase in the work of the functioning side, while for uptake on the ipsilateral side, phrenic nerve neuropathy is implicated. 6 …”