Ankle and Foot 47 - Department of Radiology - University of ...

2232 VII Imaging of the Musculoskeletal System
Figure 47-34. Normal type 1 (small) accessory
navicular (arrow in dashed magnified box).
Figure 47-35. Normal type 2 (large) accessory
navicular (white arrow in dashed magnified box).
Incidentally seen is a normal os peroneum (black
arrow).
bone itself. Patients with this normal variation are typically
asymptomatic unless they have a fracture through the
normal fibrous union between the navicular and accessory
navicular. A painful accessory navicular syndrome can be
diagnosed by MRI by the presence of marrow edema in the
accessory navicular and the adjacent navicular bone, especially
if this corresponds to the point of maximum pain
(Fig. 47-36). Normally, there should be a solid fibrous
union between the type 2 accessory navicular and the
navicular. The presence of a line of fluid between
these bones is abnormal and indicates a pseudarthrosis,
another MRI finding in accessory navicular syndrome
(Fig. 47-37).
• Os Peroneum Syndrome
The os peroneum is a common sesamoid bone located in
the peroneus longus tendon as it passes under the cuboid.
In rare cases, this normal ossicle can become inflamed and
painful. Chronic inflammation can be suspected radiographically
if the os peroneum is abnormally sclerotic,
although this finding is subjective. A more objective finding
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