American Journal of Roentgenology, Vol 164, 451-454, Copyright © 1995 by American Roentgen Ray Society
Gradient-echo MR imaging of the temporomandibular joint: diagnostic pitfall caused by the superficial temporal artery
JP Crabbe, SL Brooks and JH Lillie
Department of Radiology, University of Michigan, Ann Arbor 48109.
OBJECTIVE. In routine MR imaging of the temporomandibular joints, a low-
signal structure posterosuperior to the mandibular condyle is occasionally
seen on the two-dimensional gradient-echo sequence. The structure is ovoid
and may have a higher-signal core, simulating a loose body within the
joint. We undertook a clinical and cadaveric study to determine the cause
of this finding. MATERIALS AND METHODS. In a clinical study, we reviewed
the MR images of 100 temporomandibular joints. We scored each joint for the
presence and appearance of a low- signal structure posterosuperior to the
mandibular condyle: type 1 was ovoid with a low-signal rim and a
higher-signal core, type 2 was ovoid with uniformly low signal, type 3 was
a low-signal structure inseparable from the posterior wall of the glenoid
fossa, and type 4 was normal. Using this scoring system, we determined the
appearance and frequency of the finding on two-dimensional gradient-echo,
T1-, T2-, and proton density-weighted images. To determine the cause of the
finding, we correlated the imaging and anatomic findings in a cadaveric
specimen. RESULTS. Of the 100 MR images of joints reviewed, 22 showed a
type 1 structure, 24 a type 2 structure, 11 a type 3 structure, and 43 were
normal. The finding was seen only on the two-dimensional gradient- echo
sequences, never on the spin-echo sequences. Correlation between the
imaging and anatomic findings in the cadaveric specimen showed that the
finding was caused by the superficial temporal artery. The variability in
its appearance is thought to result from the complex manifestations of
flowing blood within this artery. CONCLUSION. The finding posterosuperior
to the mandibular condyle seen on two- dimensional gradient-echo MR images
is a flow phenomenon within the superficial temporal artery. Recognition of
the nature of this finding will avoid mistaking it for disease, such as an
intraarticular loose body.