AJR 2003; 180:99-107
© American Roentgen Ray Society
Sonography and MR Imaging of Selected Benign Masses in the Ankle and Foot
Hong Pham1,
David P. Fessell1,2,
John E. Femino3,
Susan Sharp1,
Jon A. Jacobson1 and
Curtis W. Hayes1
1 Department of Radiology, University of Michigan Medical Center, Taubman Center
(TC) 2808, 1500 E. Medical Center Dr., Ann Arbor, MI 48109-0326.
2 Present address: Akron Radiology, 525 E. Market St., Akron, OH 44304.
3 Department of Orthopedic Surgery, University of Michigan Medical Center,
Taubman Center, Ann Arbor, MI 48109-0326.
Received January 4, 2002;
accepted after revision May 13, 2002.
Address correspondence to D. P. Fessell.
Introduction
The use of MR imaging is firmly established as a means of evaluating
musculoskeletal abnormalities. Sonography is increasingly being used for
evaluation of tendons, joints, and soft-tissue abnormalities
[1]. This pictorial essay
illustrates the sonographic and MR imaging characteristics of a selected
sample of surgically resected and pathologically proven benign soft-tissue
masses of the foot and ankle, including plantar fibromatosis, schwannomas,
lipomas, glomus tumors, ganglion cysts, abscesses, epidermal inclusion cysts,
and subcutaneous granuloma annulare. Sonographic and MR imaging features can
be helpful in characterizing these lesions and, in some cases, can be useful
in determining a specific diagnosis.
Plantar Fibromatosis
Plantar fibromatosis is a benign fibroblastic proliferation of the plantar
fascia. On sonography, plantar fibromatosis appears as a fusiform, hypoechoic,
or mixed echogenic mass, frequently located in the middle or distal plantar
fascia [1] (Figs.
1A and
1B). On Doppler sonography,
plantar fibromatosis can show markedly increased flow. On MR imaging, plantar
fibromatosis appears minimally to mildly hyperintense on T1-weighted images
and can display low, high, or variable signal intensity on T2-weighted images
(Figs. 1C and
1D). Strong enhancement may be
seen after gadolinium administration
[2]. Sonographic findings can
often be strongly suggestive or diagnostic of plantar fibromatosis, especially
if the condition is bilateral. If the plantar fascia lesion shows low signal
on both T1- and T2-weighted images, findings on MR imaging can be diagnostic
for the condition.
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Fig. 1A. —33-year-old woman with plantar fibromatosis of great toe.
Longitudinal sonogram of plantar aspect of first metatarsophalangeal joint
shows unencapsulated mass (arrows) with mixed echogenicity that is
superficial relative to flexor hallucis longus tendon (arrowheads).
Proximal portion is on left, and distal portion is on right. As is
conventional in musculoskeletal sonography, superficial (plantar) portion
appears at top of image.
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Fig. 1B. —33-year-old woman with plantar fibromatosis of great toe.
Transverse sonogram of plantar aspect of great toe shows mass (between
cursors) superficial relative to flexor hallucis longus tendon
(arrowhead). At this level, mass appears isoechoic relative to
surrounding soft tissues with peripheral hypoechogenicity. Superficial
(plantar) portion is at top of image.
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Fig. 1C. —33-year-old woman with plantar fibromatosis of great toe.
Coronal T1-weighted spin-echo MR image (TR/TE, 300/14) shows mass (white
arrows) in distal plantar fascia that has ill-defined margins, is
isointense relative to muscle, and is superficial relative to flexor hallucis
longus tendon (black arrow).
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Fig. 1D. —33-year-old woman with plantar fibromatosis of great toe.
Coronal fast spin-echo inversion recovery MR image (5000/22) shows
high-signal-intensity mass (arrows) with surrounding edema
superficial relative to flexor hallucis longus tendon
(arrowhead).
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Benign Tumors of the Peripheral Nerve Sheath
Benign tumors of the peripheral nerve sheath include schwannomas and
neurofibromas. A schwannoma is a benign tumor arising from the Schwann cells
of peripheral nerve sheaths. On sonography, schwannomas are well defined and
fusiform with low to mixed echogenicity
[3] (Figs.
2A and
2B). On MR imaging, these
lesions are often well defined and hypointense on T1-weighted images and
heterogeneously hyperintense on T2-weighted images
[2]
(Fig. 2C). Like neurofibromas,
schwannomas commonly enhance after gadolinium administration
(Fig. 2D). Cystic regions and a
heterogeneous appearance are more commonly seen in schwannomas than in
neurofibromas. A lesion that is positioned eccentrically relative to the nerve
can be suggestive of a schwannoma; however, differentiation of a schwannoma
from a neurofibroma is often not possible on imaging. Schwannomas and
neurofibromas can display a target sign consisting of a central hyperechoic
region combined with a peripheral hypoechoic region on sonography. On
T2-weighted MR imaging, schwannomas and neurofibromas can display a central
hypointense region combined with a peripheral hyperintense region
[3].
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Fig. 2A. —37-year-old man with schwannoma of posterior tibial nerve.
Longitudinal sonogram shows well-defined mixed-echogenic mass (between
cursors) displacing posterior tibial nerve (arrowheads).
Flexor hallucis longus tendon is indicated by double arrowheads. Proximal
portion of nerve is left, and distal portion is right.
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Fig. 2B. —37-year-old man with schwannoma of posterior tibial nerve.
Transverse sonogram shows mixed echogenic mass (between cursors)
superficial relative to flexor hallucis longus tendon (arrowheads)
and adjacent to medial and lateral plantar branches of posterior tibial nerve
(arrows).
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Fig. 2C. —37-year-old man with schwannoma of posterior tibial nerve.
Axial T1-weighted MR image (TR/TE, 600/14) shows low-signal-intensity mass
(solid arrow) adjacent to flexor hallucis longus tendon (open
arrow) and posterior tibial vessels (arrowhead).
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Fig. 2D. —37-year-old man with schwannoma of posterior tibial nerve.
Axial T1-weighted MR image (550/14) obtained with fat saturation after IV
gadolinium administration shows that mass (arrow) is diffusely
enhanced.
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Lipomas
Lipomas are benign tumors composed of aggregates of mature adipocytes. On
sonography, they display variable echogenicity and often are elliptical and
well defined, with the largest dimension parallel to the skin
[1] (Fig.
3A,3B).
On MR imaging, lipomas have the same intensity as subcutaneous fat on both T1-
and T2-weighted images and may contain regions of variable signal
characteristics caused by fibrosis, hemorrhage, infarction, calcification, or
ossification [2] (Fig.
4A,4B).
Lipomas have no internal flow on color Doppler sonography, and they do not
enhance after the administration of contrast material. Sonographic findings
can strongly suggest the presence of soft-tissue lipomas, and MR imaging can
provide a definitive diagnosis of this entity.
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Fig. 3A. —36-year-old woman with lipoma in dorsal aspect of foot.
Longitudinal sonogram shows 2-cm-long subcutaneous mass (between
cursors) that is isoechoic compared with surrounding subcutaneous
tissue and superficial relative to cortex (arrowheads) of tarsal
bones.
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Fig. 3B. —36-year-old woman with lipoma in dorsal aspect of foot.
Transverse sonogram shows subcutaneous mass (between cursors)
measuring 1.8 x 0.8 cm that is isoechoic relative to surrounding
subcutaneous tissues.
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Fig. 4A. —59-year-old woman with lipoma in anterior aspect of ankle.
Axial T1-weighted spin-echo MR image (TR/TE, 500/14) shows
high-signal-intensity mass (arrowheads) with well-defined lateral
borders surrounding anterior tibial tendon (arrow). Diameter of
anterior tibial tendon may be mildly enlarged.
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Fig. 4B. —59-year-old woman with lipoma in anterior aspect of ankle.
Sagittal T1-weighted spin-echo MR image (500/14) shows high-signal-intensity
mass (arrows) at level of anterior tibiotalar joint. Anterior border
(arrowheads) is well defined.
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Glomus Tumors
Glomus tumors are benign hamartomatous tumors of the neuoromyoarterial
glomus body of the distal digits. On sonography, they are well defined, ovoid
masses that appear homogeneously hypoechoic
[4]
(Fig. 5A). On MR imaging,
glomus tumors are well defined and hypointense on T1-weighted images and
strongly hyperintense on T2- or proton density—weighted images (Figs.
5B and
5C). These tumors strongly
enhance after gadolinium administration
[5].
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Fig. 5A. —34-year-old man with dorsolateral glomus tumor at fifth
metatarsal bone. Longitudinal sonogram shows hypoechoic mass (large
arrows) superficial to insertion of peroneus brevis (small
arrows) on base of fifth metatarsal bone (arrowheads).
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Fig. 5B. —34-year-old man with dorsolateral glomus tumor at fifth
metatarsal bone. Coronal T1-weighted spin-echo MR image (TR/TE, 616/14) shows
isointense mass (arrow) adjacent to fifth metatarsal bone.
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Fig. 5C. —34-year-old man with dorsolateral glomus tumor at fifth
metatarsal bone. Coronal proton density—weighted fast spin-echo MR image
(5000/15) obtained with fat saturation shows high-signal-intensity mass
(arrow).
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Ganglion Cysts (Ganglia)
Ganglia are cystic lesions filled with gelatinous fluid usually located
near, and in some cases communicating with, a joint or tendon sheath. On
sonography, ganglia are well defined with a spectrum of imaging appearances
ranging from completely anechoic to hypoechoic with multiple internal
septations [1]
(Fig. 6A). Ganglia also appear
well defined on MR imaging; these lesions are hypointense on T1-weighted
imaging and hyperintense on T2- or proton density—weighted imaging
[2]
(Fig. 6B) with varying amounts
of septations. No internal enhancement on MR imaging or internal flow on color
Doppler sonography is noted with ganglion cysts. Both sonography and MR
imaging can reveal a ganglion cyst.
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Fig. 6A. —51-year-old woman with dorsolateral ganglion cyst in foot.
Longitudinal sonogram shows well-defined anechoic mass (large arrows)
superficial to cortex of cuboid bone (arrowheads). Posterior acoustic
enhancement (small arrows) is visible.
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Fig. 6B. —51-year-old woman with dorsolateral ganglion cyst in foot.
Coronal proton density—weighted fast spin-echo MR image (TR/TE, 3000/15)
shows multilobular high-signal mass (arrow) superficial to cuboid
bone. Although communicating neck is not visualized, location of mass
indicates that origin of mass is likely intertarsal joints or tendon
sheath.
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Abscesses
An abscess is a focal collection of purulent fluid surrounded by inflamed
tissue. On sonography, abscesses are often well defined, with an echogenicity
ranging from hypoechoic to hyperechoic
[1] (Figs.
7A and
7B). Features such as internal
septations and debris, the swirling of fluid in the abscess after compression
with the transducer, an absence of internal flow, and surrounding hyperemia on
color Doppler sonography can aid in establishing the diagnosis of an abscess
[1]. On MR imaging, abscesses
have homogeneously or heterogeneously low signal intensity on T1-weighted
images and intermediate to high signal intensity on T2-weighted images (Figs.
7C and
7D). Enhancement of the
surrounding soft tissues after gadolinium administration is characteristic of
an abscess. In the proper clinical setting, abscesses can be definitively
diagnosed on the basis of sonographic or MR imaging findings. Sonography can
also be used to guide aspiration of an abscess.
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Fig. 7A. —81-year-old woman with abscess in dorsal aspect of forefoot.
Longitudinal sonogram obtained between first and second metatarsal bones shows
hypoechoic mass (straight arrows) with dependent echoes, internal
septation (arrowheads), and posterior acoustic enhancement
(curved arrow).
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Fig. 7C. —81-year-old woman with abscess in dorsal aspect of forefoot.
Coronal T1-weighted spin-echo MR image (TR/TE, 400/9) shows low-signal mass
(arrows) between first and second metatarsal bones.
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Fig. 7D. —81-year-old woman with abscess in dorsal aspect of forefoot.
Gadolinium-enhanced coronal T1-weighted spin-echo MR image (350/9) with fat
saturation shows that mass (arrows) displays no enhancement, although
surrounding soft tissues have enhanced.
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Epidermal Inclusion Cysts
Epidermal inclusion cysts are true epithelially lined cysts that can be
filled with keratin and a varying amount of lipid-containing debris. On
sonography, these lesions appear as solid, well-defined, echogenic masses with
internal echoes resulting from the presence of debris
[6]
(Fig. 8A). On MR imaging,
epidermal inclusion cysts are well-defined circumferential masses that are
either isointense or slightly hyperintense on T1-weighted images
(Fig. 8B). On T2-weighted
images, these cysts are typically hyperintense and can show focal areas of
decreased signal because of dependent debris
[2]. Mild enhancement of such
cysts can be seen on gadolinium-enhanced MR images
(Fig. 8C).
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Fig. 8A. —33-year-old man with plantar epidermal inclusion cyst at
fifth metatarsal bone. Transverse power Doppler sonogram shows well-defined
mass (large arrows), isoechoic relative to surrounding soft tissues,
with internal blood flow at deepest portion of mass (small arrows).
Arrowheads mark cortex of fifth metatarsal bone. Superficial (plantar) portion
is at top of image.
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Fig. 8B. —33-year-old man with plantar epidermal inclusion cyst at
fifth metatarsal bone. Coronal T1-weighted spin-echo MR image (TR/TE, 650/14)
shows low-signal mass (arrow) superficial relative to fifth
metatarsal bone.
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Fig. 8C. —33-year-old man with plantar epidermal inclusion cyst at
fifth metatarsal bone. Coronal T1-weighted spin-echo fat-saturated MR image
(650/14) obtained after IV gadolinium administration shows mild enhancement of
mass (arrow).
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Subcutaneous Granuloma Annulare
Subcutaneous granuloma annulare is an inflammatory dermatosis in which
nodules typically grow in a papular, ringlike pattern. On sonography, these
lesions are often ill defined and hypoechogenic with no internal flow on
Doppler sonography [7] (Figs.
9A and
9B). On MR imaging,
subcutaneous granuloma annulare appears ill defined and relatively isointense
relative to muscle on T1-weighted images. Signal intensity on T2- and proton
density—weighted MR images can be low or heterogeneously hyperintense
(Fig. 9C), as noted in all six
of the cases reported by Chung et al
[8]. These lesions enhance
after administration of contrast material
[7,
8] (Figs.
9D and
9E).
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Fig. 9A. —23-year-old woman with subcutaneous granuloma annulare
superficial relative to insertion of Achilles tendon. Longitudinal sonogram
shows mass of mixed echogenicity (between cursors) superficial
relative to insertion of Achilles tendon (arrowheads) on calcaneal
cortex (arrows).
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Fig. 9B. —23-year-old woman with subcutaneous granuloma annulare
superficial relative to insertion of Achilles tendon. Transverse sonogram
shows that mass (between cursors) has regions of hypoechogenicity and
isoechogenicity. Achilles tendon (arrowhead) and calcaneus
(arrows) are visible.
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Fig. 9C. —23-year-old woman with subcutaneous granuloma annulare
superficial relative to insertion of Achilles tendon. Axial proton
density—weighted fast spin-echo MR image (TR/TE, 3250/16) obtained with
fat saturation shows heterogeneous high signal intensity with focal region of
increased signal (arrow) consistent with that of fluid.
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Fig. 9D. —23-year-old woman with subcutaneous granuloma annulare
superficial relative to insertion of Achilles tendon. Axial T1-weighted
spin-echo fat-saturated MR image (416/10) obtained after IV gadolinium
administration shows strong enhancement (straight arrows) medially.
Lateral fluid component (curved arrow) displays no enhancement.
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Fig. 9E. —23-year-old woman with subcutaneous granuloma annulare
superficial relative to insertion of Achilles tendon. Sagittal T1-weighted
spin-echo fat-saturated MR image (700/10) obtained after IV gadolinium
administration shows craniocaudal extent of mass (arrows).
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In summary, the sonographic and MR imaging characteristics of many
soft-tissue masses found in the foot and ankle are nonspecific. Plantar
fibromatosis, ganglionic cysts, and abscesses can often be definitively
diagnosed on the basis of the findings of either modality. For soft-tissue
lipomas, sonographic findings can be strongly suggestive and MR imaging can
help in establishing a definitive diagnosis. When definitive diagnosis is not
possible, sonography and MR imaging can help one to narrow the differential
diagnosis and provide valuable information regarding the size, location, and
involvement of surrounding tendons, nerves, and vessels. This information aids
in surgical planning. Sonography can also be used to guide biopsy or
aspiration.
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Introduction
Plantar Fibromatosis
