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

2312 VII Imaging of the Musculoskeletal System
A B C
Figure 47-117. Plantar fibroma in a 44-year-old.
Coronal T1-weighted (A), proton-density–weighted
(B), and T2-weighted (C) images reveal that the lesion
(arrows) is relatively dark on all sequences and
confined to the fat of the plantar heel pad.
and it is not uncommon for cultures of such aspirates to
yield no growth. Clinical symptoms are often mild, generally
presenting with persistent local pain.
Radiographs show an intramedullary lucency with surrounding
sclerosis, the density of which depends on the
chronicity of the abscess. A thick chronic periosteal reaction
may also be present (Fig. 47-116B). MRI after the
administration of IV contrast reveals an intraosseous
abscess with peripheral but not central enhancement
(Fig. 47-116E). 29
Tumors
• Soft Tissue Masses
Soft tissue tumors of the feet and ankle are common, and
MRI is useful in determining the tissue type as well as
demonstrating the relationship of the mass to the adjacent
anatomic structures. Synovial cysts or ganglia are among
the most common soft tissue “masses” found around the
foot and ankle. These are uniformly bright on fluidsensitive
images and exhibit minimal if any peripheral
enhancement after the administration of IVGd-based contrast
(see Fig. 47-57). In comparison, nerve sheath tumors
such are schwannomas are heterogeneously bright on T2-
weighted and inversion recovery images, and they demonstrate
heterogeneous contrast enhancement (see Fig.
47-56).
Plantar fibromas can have variable signal characteristics
but are typically dark on all sequences (Fig. 47-117).
These are usually found in the plantar fat adjacent to the
aponeurosis, usually close to the calcaneus.
Morton’s neuromas usually occur between the heads
of the second and third or third and fourth metatarsals and
are also usually dark on noncontrast images, although they
can exhibit postcontrast enhancement (see Fig. 47-58).
Giant cell tumor of the tendon sheath is a localized
form of pigmented villonodular synovitis, the latter being
a joint-centered synovial proliferative condition. Both diseases
show areas of decreased signal on T1-images, protondensity–images,
and T2-weighted images, secondary to
hemosiderin deposition (Fig. 47-118A to C). The presence
of hemosiderin can be detected on gradient echo and precontrast
fat-suppressed T1-weighted images (Fig. 47-118D),
and the vascularized proliferative synovium should exhibit
some contrast enhancement (Fig. 47-118E).
• Bone Tumors 28
Osseous tumors are much less common than soft tissue
tumors of the foot and ankle. Like all bone lesions, these
tumors should be initially evaluated radiographically. MRI,
however, is useful in localizing tumors and staging their
extent. Because most tumors have nonspecific signal characteristics,
MRI is often unable to render a specific preoperative
diagnosis.
Primary bone tumors of the feet are rare, accounting
for only 4% of all bone tumors. 20 Benign bone neoplasms
are more common than malignant ones, although in the
foot, most bone neoplasms are primary tumors because
metastases to the foot are rare.
• Benign Tumors
The most common benign tumors of the foot are enchondromas
and osteoid osteomas. An osteoid osteoma is a relatively
common cause of bone pain in adolescents and young
adults, accounting for approximately 10% of all benign
bone tumors. The classic history is pain at night, relieved by
aspirin. Osteoid osteomas are one of the few tumors that
are better imaged by CT than MRI. Thin-slice CT well demonstrates
the lucent nidus as well as the tiny sclerotic component
that is characteristically associated with it (Fig.
47-119A). CT is also used by radiologists for the purpose of
percutaneously ablating the nidus. On MRI, osteoid osteomas
are seen as a nonspecific edema pattern emanating
from a tiny, dark nidus (see Fig. 47-119B to D).
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