AJR 2005; 184:979-983
© American Roentgen Ray Society
MRI of Medial Malleolar Bursa
Robert R. Brown1,2,
Zehava Sadka Rosenberg3,
Mark E. Schweitzer3,
Steven Sheskier4,
Donna Astion5 and
Jeffrey Minkoff6
1 Cleveland Clinic, Cleveland, OH.
2 Current address: Advanced Concepts in Medical Imaging, Ft. Lauderdale,
FL.
3 Department of Radiology, The Hospital for Joint Diseases and New York
University Medical Center, 301 E 17th St., New York, NY 10003.
4 Orthopedic Department, Hospital for Joint Diseases and New York University
Medical Center, New York, NY 10003.
5 St Lukes Roosevelt Hospital Manhattan, New York, NY 10011.
6 Minkoff Sportspedic Associates, PA, Delray Beach, FL.
Received March 4, 2004;
accepted after revision June 9, 2004.
Presented at the 2001 meeting of the Radiological Society of North America,
Chicago, IL.
Address correspondence to Z. S. Rosenberg.
Abstract
OBJECTIVE. This study was designed to assess the MR appearance of
the medial perimalleolar fat in an asymptomatic population and describe the
MRI appearance of the medial malleolar bursa.
CONCLUSION. The MRI findings of medial perimalleolar fat in
asymptomatic individuals and in patients with suspected medial malleolar bursa
include normal fat, minimal or extensive subcutaneous edema, and a
fluid-filled sac. The latter pattern is consistent with the MR appearance of
the medial malleolar bursa.
Introduction
Bursitis in the foot and ankle, a common cause of ankle pain, may present
with focal tenderness or with generalized aching and discomfort
[1–3].
The medial malleolar bursa, an adventitial bursa, may develop over the medial
malleolus (Fig. 1) in response
to abnormal pressure, usually from footwear that closely approximates the
ankle, such as boots, skates, and high-top shoes
[4,
5]. The rise in popularity of
sporting activities that require tight-fitting boots, such as figure skating
and ice hockey, has led to an increased incidence of painful medial malleolar
bursitis [5].
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Fig. 1. —Drawing of medial malleolar bursa shows medial malleolar bursa is
located in superficial fat adjacent to medial malleolus. Reprinted with
permission from Robert Cravero, Cleveland Clinic, Weston, OH, 2002.
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The MR characteristics of medial malleolar bursitis have not yet been
described, to our knowledge, in the radiology or orthopedics literature. This
retrospective study was performed to examine the MR appearance of the medial
malleolar subcutaneous fat in the asymptomatic population and describe the MR
appearances of painful medial malleolar bursa.
Materials and Methods
Asymptomatic Volunteers
To establish a reference guideline for the appearance of the perimalleolar
subcutaneous fat in the asymptomatic population, two musculoskeletal
radiologists reviewed by consensus the MRI studies of 35 ankles from 29
asymptomatic volunteers (nine women, 20 men; average age, 38 years). The
reviewers noted signal alterations of the medial perimalleolar fat. Axial and
sagittal T1-weighted images were obtained in each patient. In 15 cases, axial
T2-weighted spin-echo images were also obtained (TR range/TE,
4,000–5,000/80; 5-mm slice thickness; 256 x 256 matrix; number of
excitations, 2; 14 x 14 field of view).
Patient Population
Ankle MR examinations of 10 patients (five women, five men; age range,
25–52 years; mean age, 35 years) with unilateral medial ankle pain, a
mass suspicious for medial malleolar bursa, or both were retrospectively
reviewed. Medical records for each patient were reviewed for relevant history
and clinical assessment. Six of the patients had a well-defined palpable mass
superficial to the medial malleolus. Six patients were professional or
recreational figure skaters (n = 2) and ice hockey players
(n = 4) who regularly wore close-fitting boots. One of the patients
who was an ice hockey player described onset of pain after being hit with a
puck in the medial malleolar region. One other patient developed a mass after
removal of a surgical screw from the medial malleolus. Three patients did not
have any known predisposing factors. None of the patients had other clinical
findings to explain their medial ankle pain such as inflammatory arthritis or
posterior tibial tendon dysfunction. Aside from the MR signal alterations in
the medial subcutaneous fat, none of the patients had other MR diagnoses that
could account for the medial ankle pain such as deltoid injury, posterior
tibial tendon dysfunction, or osteochondral talar lesion.
Two musculoskeletal radiologists reviewed the MRI studies in consensus. The
MR sequences obtained for each study included both axial T1-weighted and
fluid-sensitive sequences (inversion recovery images or T2-weighted fast
spin-echo images with fat saturation). Sagittal or coronal inversion recovery
images or T2-weighted fast spin-echo images with fat saturation were useful in
determining the craniocaudal extent of signal change in the perimalleolar fat.
The average field of view was 14 x 10 cm. In four patients,
fat-suppressed T1-weighted images were obtained before and after IV injection
of gadolinium.
The subcutaneous fat adjacent to the medial malleolus was assessed for
signal alterations and for the presence of a medial malleolar bursa. The
signal alterations in the fat were defined as mild if the subcutaneous edema
measured less that 2 cm in its largest diameter. Significant edema was defined
when extensive subcutaneous edema measuring more than 2 cm in its largest
diameter was noted. The medial malleolar bursa was defined as a well-defined
nonenhancing mass, with fluid signal characteristics in the perimalleolar,
subcutaneous fat superficial to the medial malleolus and anteromedial to the
posterior tibial tendon. The presence of the bursa was assessed on
T1-weighted, T2-weighted, fat-suppressed, and STIR sequences. Imaging findings
were characterized for size, shape, and extent of signal alteration.
Results
Twenty-eight (80%) the asymptomatic individuals had a normal appearance to
the perimalleolar fat with no abnormal signal detected on either T1-weighted
or T2-weighted images. Seven (20%) of the 35 asymptomatic individuals had
signal alterations measuring less than 2 cm that were consistent with mild
edema in the perimalleolar fat (Fig.
2).
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Fig. 2. —Mild edematous stranding of medial perimalleolar fat in 23-year-old
asymptomatic male volunteer. T2-weighted image (TR/TE, 5,000/80) shows edema
in subcutaneous fat adjacent to medial malleolus (arrows).
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Six of our 10 patients had a discrete mass adjacent to the medial malleolus
with signal characteristics consistent with fluid—that is, low on
T1-weighted images and bright on T2-weighted and fat-suppressed or STIR images
(Figs. 3A,
3B, and
4). In four of these patients,
the mass was homogeneous on all pulse sequences. The masses ranged in size
from 1 to 2 cm in the medial to lateral dimension, 1 to 3 cm in the
anteroposterior dimension, and 1.5 to 6 cm in the craniocaudal dimension.
There was only peripheral enhancement after contrast administration in four
patients who received gadolinium, which confirmed the presence of a fluid
collection. In two other cases, areas of low signal intensity were noted
adjacent to or within the sac on both T1-weighted and fluid-sensitive images
suggesting fibrosis and scarring (Figs.
5A and
5B).
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Fig. 3A. —Surgically proven discrete adventitial bursal sac in 22-year-old
female ice skater. Axial T1-weighted (A) (TR/TE, 450/15) and axial
fat-saturated T2-weighted fast spin-echo (B) (2,500/90) images show
mass with well-defined borders and fluid signal characteristics
(arrow) in subcutaneous soft-tissues.
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Fig. 3B. —Surgically proven discrete adventitial bursal sac in 22-year-old
female ice skater. Axial T1-weighted (A) (TR/TE, 450/15) and axial
fat-saturated T2-weighted fast spin-echo (B) (2,500/90) images show
mass with well-defined borders and fluid signal characteristics
(arrow) in subcutaneous soft-tissues.
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Fig. 4. —Surgically-proven discrete adventitial bursal sac in 27-year-old
male ice hockey player. Axial fat-suppressed image (TR/TE, 3,400/43) depicts
mass (arrow) with fluid signal characteristics in subcutaneous fat
posteromedial to medial malleolus. Soft-tissue edema is noted adjacent to
mass.
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Fig. 5A. —Partly scarred down bursal sac in 15-year-old female ice skater.
Patient's symptoms improved with modification of skates. Sagittal T1-weighted
image (TR/TE, 516/18) shows homogeneous mass (arrow) posterior to
posterior tibial tendon (arrowhead). M = medial malleolus.
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Fig. 5B. —Partly scarred down bursal sac in 15-year-old female ice skater.
Patient's symptoms improved with modification of skates. Axial STIR image
(6,300/60) depicts heterogeneous increased signal of mass (arrow),
which is compatible with fibrosis of a bursal sac.
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In three patients, there was no soft-tissue mass, but significant focal
soft-tissue edema in the perimalleolar fat without well-defined margins was
noted. These focal areas ranged from 1 to 2 cm in the medial to lateral
dimension, 3 to 6 cm in the anteroposterior dimension, and 3 to 8 cm in the
craniocaudal dimension (Figs.
6A,
6B, and
6C). The perimalleolar fat was
normal in one patient.
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Fig. 6A. —39-year-old female volunteer with significant soft-tissue swelling
over medial malleolus. Axial T1-weighted (A) (TR/TE, 766/22), axial
T2-weighted (B) (3,000/90), and sagittal STIR (C) (3,300/21)
images show large region of increased signal (arrows, A and
B) in perimalleolar fat superficial to distal tibia. Margins of
edematous area are not well defined (arrowheads, C).
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Fig. 6B. —39-year-old female volunteer with significant soft-tissue swelling
over medial malleolus. Axial T1-weighted (A) (TR/TE, 766/22), axial
T2-weighted (B) (3,000/90), and sagittal STIR (C) (3,300/21)
images show large region of increased signal (arrows, A and
B) in perimalleolar fat superficial to distal tibia. Margins of
edematous area are not well defined (arrowheads, C).
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Fig. 6C. —39-year-old female volunteer with significant soft-tissue swelling
over medial malleolus. Axial T1-weighted (A) (TR/TE, 766/22), axial
T2-weighted (B) (3,000/90), and sagittal STIR (C) (3,300/21)
images show large region of increased signal (arrows, A and
B) in perimalleolar fat superficial to distal tibia. Margins of
edematous area are not well defined (arrowheads, C).
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Surgical removal of the mass was performed in four patients who had both
clinical and MR evidence of a well-defined mass. The histopathology was
consistent with a bursal sac with synovial-like tall columnar cells lining the
sac. In a fifth patient, a steroid injection into the sac produced relief of
symptoms. The remaining five patients were treated conservatively with
modification of footwear, rest, and antiinflammatory medication and
experienced good results of the treatment regimen.
Discussion
Bursae help reduce friction and facilitate gliding motion between opposing
surfaces and commonly separate tendons from adjacent structures such as
tendons, muscle, ligament, and underlying bony surfaces
[2,
3,
6,
7]. Congenital bursae develop
in utero. They are constant, usually deep, bursae that communicate with the
adjacent joint. Anatomic bursae develop in children at sites of normal
friction, whereas adventitial bursa develops in adults as a result of
excessive friction between soft-tissue and underlying bony protuberances. The
latter are frequently subcutaneous. In addition, they are not true
synovial-lined potential spaces, as are congenital bursae, and therefore are
not expected to become inflamed in a synovial inflammatory disease process,
such as rheumatoid arthritis.
In the foot and ankle, adventitial bursa may develop almost anywhere,
usually adjacent to bony prominences
[2,
3,
6,
7]. Common locations are over
the medial aspect of the first metatarsal head, underneath the metatarsal
heads, and over the exostosis dorsal to the first metatarsal head.
Medial and lateral malleolar bursae are related to friction adjacent to the
malleoli [4,
5,
8–10].
Symptomatic medial malleolar bursitis has become more prevalent because of the
popularity of athletic activities requiring tight-fitting shoes and boots,
such as figure skating and ice hockey
[4,
5,
8]. Development of a lateral
malleolar bursa has been associated with sitting habits and work-related boots
that produce persistent pressure on the lateral malleolus
[9,
10]
The cause of medial malleolar bursitis in our patients was similar to that
described in the literature. Six of our patients were competitive skaters (two
figure skaters and four hockey players). The cause for medial malleolar
bursitis in two of the patients was not known. It would be interesting to
correlate the style of daily footwear in these patients with their MRI
findings.
The friction generated against the malleoli from the boot lining or sitting
habits results in the formation of an inflamed and painful adventitial bursa.
Clinically, patients describe pain, swelling, or both over the medial aspect
of the ankle. There may be point tenderness and an associated soft-tissue mass
noted at physical examination. Although the clinical history and physical
examination may be sufficient for making the diagnosis of medial malleolar
bursitis, imaging studies may be useful in delineating the size and extent of
the medial malleolar bursa and in distinguishing this condition from
differential diagnostic considerations of medial ankle mass such as
soft-tissue tumors, ganglia, abscesses, and tenosynovitis of the posterior
tibial tendon.
The histopathologic mechanism for the formation of a subcutaneous
adventitial bursa has been described by Jaffe
[11]. Initially, there is
coalescence of preexisting minute spaces in loose connective tissue. As the
bursa develops further, its walls, by their greater density, become
differentiated from the adjacent connective tissue and a well-defined sac is
formed. The lining of the sac is formed by synoviallike tall columnar cells
rather than by true synovial cells.
Our findings are consistent with the histopathologic mechanism described by
Jaffe [11]. Four MR
appearances of the perimalleolar fat were noted in our study. The MR
appearances in the asymptomatic population were as follows: normal
subcutaneous fat (n = 28) and mild edematous stranding (n =
7). In the symptomatic patients, the changes in the region of the
perimalleolar fat included normal fat (n = 1); extensive,
subcutaneous edema (n = 3); and a discrete, nonenhancing mass
(n = 6) with well-defined margins and signal characteristic
compatible with fluid on all pulse sequences.
We postulate that the mild edematous stranding within the perimalleolar
area, noted in seven of the asymptomatic volunteers, may reflect the earliest
evidence of friction in the subcutaneous fat. With greater friction,
significant subcutaneous edema—as noted in 30% of the symptomatic
patients—represents a more advanced prebursal stage. Finally, once the
fluid vacuoles coalesce, a well-formed bursal sac—as was detected in 60%
of the symptomatic patients—develops.
The MRI findings in our study are reminiscent of the MRI features of the
prepatellar bursa, also a subcutaneous adventitial bursa
[12]. Poorly marginated edema
in the subcutaneous fat is frequently encountered in asymptomatic individuals,
whereas a well-defined fluid collection is noted in symptomatic patients.
In two patients, in addition to the fluid signal characteristics, areas of
low-signal-intensity stranding were also present on both T1-weighted and
T2-weighted images. One of these patients underwent surgery, and fibrosis and
scarring of the bursal wall were noted. This finding is consistent with
previous reports of scarring of a bursa, which is possibly secondary to prior
bursal inflammation or bleeding
[8].
All the asymptomatic individuals had either normal (80%) or mild (20%)
edema in the medial perimalleolar fat. Conversely, except one patient with
normal fat, all the patients had either significant perimalleolar edema (30%)
or a discreet fluid-filled mass (60%). These findings suggest that normal fat
or mild edema may be of no clinical significance and a well-defined bursal sac
or extensive perimalleolar edema is usually associated with medial ankle pain.
Nevertheless, we believe that caution should be exercised before invoking
extensive perimalleolar edema as the cause of a patient's symptoms. In our
experience, perimalleolar subcutaneous edema, even when extensive, can be a
fairly common MR finding in some patient populations. Thus, its association
with symptoms is not always easy to determine. For example, we have frequently
encountered extensive perimalleolar edema in patients with posterior tibial
tendon dysfunction where, we suspect, the flatfoot deformity produces
increased perimalleolar pressure. We recommend that a careful MR examination
be performed and that all other causes of medial ankle pain be excluded before
edema is considered the cause for a patient's pain.
This study has several limitations. The study was retrospective in nature,
and the patient population was small. We excluded patients with obvious causes
of medial-sided abnormalities, such as posterior tibial tendon abnormalities,
inflammatory arthritis, or acute traumatic injuries to the bone or deltoid
ligament. Nevertheless, it is possible that a few patients may have had other
unrecognized conditions. In addition, only four of our patients had surgical
correlation. Medial malleolar bursitis is usually treated conservatively with
nonoperative measures such as modifying footwear, using doughnut-shaped
cushions to protect the inflamed area, skate stretching, or steroid injection
[8]. Surgery has been reserved
for the rare cases in which the medial malleolar bursitis is refractory to
conservative treatment [4].
In conclusion, signal alterations in the perimalleolar fat in our study
included mild edema, significant edema, and a well-defined fluid-filled sac.
Partial scarring can also be encountered. A well-defined perimalleolar
fluid-filled sac is indicative of a medial malleolar bursa and is often
associated with pain and poorly fitting footwear.
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Abstract
Introduction
