Direct relationship between cell density and FDG uptake in asymptomatic aortic aneurysm close to surgical threshold: an in vivo and in vitro study.
OBJECTIVE
Conflicting results have been reported about the clinical value of fluorodeoxyglucose (FDG) imaging in predicting the risk of rupture of abdominal aortic aneurysm (AAA). The present study tests the hypothesis that FDG uptake is low in asymptomatic noninflammatory AAA due to the low cell density in aneurysmal walls.


METHODS
Positron emission tomography (PET)/CT imaging was performed in 12 consecutive candidates for AAA surgical repair and in 12 age- and sex-matched controls. At intervention, aneurysmal walls were cut into three sequential blocks. Block A was frozen to cut three 5-μm slices for incubation with 2-3 MBq of FDG for 5 min. Block C was first incubated with the same tracer solution for the same time and subsequently frozen to cut three 5-μm slices. Autoradiographic images were coregistered with immunohistochemical pictures of cell density, type and DNA synthesis as assessed on block B.


RESULTS
No visible uptake in abdominal aorta occurred in any patient or control subject. Immunohistochemistry documented a severe loss of wall structure, with low numbers of cells. Tracer retention directly correlated with overall cell density and with prevalence of cells synthesizing DNA. The metabolic nature of FDG uptake was confirmed by the selective effect of preliminary freezing that decreased tracer content by 90% in regions with high cell density and only by 34% in cold acellular areas.


CONCLUSIONS
The loss of tissue structure and the marked decrease in cell density account for the low prevalence of positive findings at FDG PET imaging, at least in asymptomatic patients bearing AAAs whose diameter is close to surgical indication.
CNR Institute of Bioimaging and Molecular Physiology, Milan, Genoa Section, Genoa, Italy. Cecilia.Marini@unige.it
Cecilia
C
Marini
Silvia
S
Morbelli
Riccardo
R
Armonino
Giovanni
G
Spinella
Mattia
M
Riondato
Michela
M
Massollo
Francesca
F
Sarocchi
Bianca
B
Pane
Carla
C
Augeri
Luca
L
Abete
Giorgio
G
Ghigliotti
Daniela
D
Palmieri
Francesco
F
Fiz
Giuseppe
G
Cittadini
Ezio
E
Fulcheri
Domenico
D
Palombo
Gianmario
G
Sambuceti
D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology* / Q000601:surgery; D058070:Asymptomatic Diseases; D001345:Autoradiography; D001692:Biological Transport; D002452:Cell Count; D002470:Cell Survival; D015925:Cryopreservation; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008297:Male; D011877:Radionuclide Imaging
D019788:Fluorodeoxyglucose F18; D005947:Glucose