DOI:10.2214/AJR.04.1486
AJR 2005; 185:1449-1452
© American Roentgen Ray Society
Prominent Vascular Remnants in the Calcaneus Simulating a Lesion on MRI of the Ankle: Findings in 67 Patients with Cadaveric Correlation
Jacob L. Fleming, II,
Leslie Dodd and
Clyde A. Helms
Department of Radiology, Duke University Medical Center, Box 3808,
Durham, NC 27710.
Received September 20, 2004;
accepted after revision December 6, 2004.
Address correspondence to J. L. Fleming II
(jfleming{at}sjha.org).
Abstract
OBJECTIVE. Our objective was to prove through cadaveric correlation
that a frequently seen focus of MRI signal in the calcaneus is benign.
CONCLUSION. A characteristic focus of signal (increased T2,
decreased T1) in the calcaneus near the attachment of the cervical and
interosseous ligaments is a common, benign finding frequently seen on MRI of
the foot and ankle.
Introduction
MRI has proven useful in examining the painful ankle, including the
detection of subtle marrow abnormalities
[1-3].
As with many imaging techniques, however, MRI of normal variants or benign
findings has been shown to cause false-positive interpretations
[3]. We believe this to be the
case with a characteristic focus of signal that is frequently seen on routine
MRI of the foot and ankle. This focus of MRI signal is located within the
calcaneus near the insertion of the cervical and interosseous ligaments and
manifests as a focus of increased T2 and decreased T1 signal (Figs.
1A, and
1B). Although this finding is
unlikely to be misinterpreted as significant pathology by an experienced
musculoskeletal radiologist, several patients have been referred to our
institution for biopsy of this exact lesion. To our knowledge, this finding
has not been described in the medical literature. The purpose of this report
is to better characterize this focus of MRI signal within the calcaneus and to
show through cadaveric correlation that this is a benign finding.
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Fig. 1A —33-year-old male runner with lateral ankle pain. Conventional
spin-echo T1-weighted (TR/TE, 500/15) (A) and fast spin-echo
T2-weighted (3,000/70) (B) sagittal MR images of ankle show focus of
increased T2 (white arrow) and decreased T1 (black arrow)
signal within calcaneus in characteristic subtalar location. Lesion measured
greater than 5 mm and was considered large.
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Fig. 1B —33-year-old male runner with lateral ankle pain. Conventional
spin-echo T1-weighted (TR/TE, 500/15) (A) and fast spin-echo
T2-weighted (3,000/70) (B) sagittal MR images of ankle show focus of
increased T2 (white arrow) and decreased T1 (black arrow)
signal within calcaneus in characteristic subtalar location. Lesion measured
greater than 5 mm and was considered large.
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Materials and Methods
A retrospective review was performed of 67 consecutive patients who
underwent MRI of the ankle at our institution from January 2001 to March 2002.
The main indications for the studies included acute and chronic pain, trauma,
tumor, and infection. This patient population consisted of 29 males and 38
females (age range, 11-73 years; mean age, 40 years). All patients were imaged
using our standard MRI ankle protocol, which consists of T1- and fast
spin-echo fat-suppressed T2-weighted images (TR/TE, 500/14 and TR range/TE,
3,000-4,000/70, respectively) acquired in the sagittal, coronal, and axial
planes. Additional technical factors included a 1.5-T magnet; echo-train
length, 4; surface coil; 4-mm thick slices; 12 cm field of view; matrix, 256
x 192; and two averages. Two observers, one musculoskeletal attending
radiologist and one radiology resident, evaluated each case in consensus for
the presence or absence of this specific focus of signal in the subtalar
region. When present, this focus of MRI signal was classified according to
size: < 3 mm (small), 3-5 mm (medium), and > 5 mm (large). This cohort
was divided into three age groups: 0-30, 31-50, and 51-75 years.
To obtain a pathologic specimen that contained this characteristic focus of
MRI signal, the bilateral ankles of two cadavers were imaged. From the four
cadaveric ankles imaged, two gross specimens were obtained, one from the
largest lesion found in a single ankle from each cadaver. Both cadaveric
specimens were then evaluated grossly and histologically by a board-certified
pathologist. The data on these patients were gathered by a third party and
made anonymous by having the names and patient identification removed; thus,
institutional review board approval was not necessary at our institution.
Exclusion criteria included pathology in the calcaneus that obscured
visualization of the characteristic location of this focus of MRI signal.
Three patients were excluded from the study secondary to severe subtalar
pathology that obscured the region of interest. Two of these patients had
osteomyelitis and one had severe subtalar degenerative changes involving the
calcaneus.
Results
Seventy-two ankles were evaluated. Five patients had their bilateral ankles
imaged. Seventy-five percent (52/69) of the ankles reviewed contained the
characteristic (increased T2, decreased T1) focus of signal. Seventy-five
percent (21/28) of the male ankles and 76% (31/41) of the female ankles
contained this focus of signal. Seven percent (5/69) contained a large focus
of increased T2 signal (Figs.
1A, and
1B), 19% (13/69) contained a
medium-sized focus (Figs. 2A,
2B, and
2C), and most (48%; 33/69)
contained a small subtalar focus of signal
(Fig. 3). Twenty-six percent
(18/69) did not contain a focus of signal and were classified as negative
examinations.
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Fig. 2A —18-year-old male basketball player with history of multiple
ankle sprains. Fast spin-echo T2-weighted (TR/TE, 4,000/70) sagittal
(A), axial (B), and coronal (C) MR images of ankle show
medium-sized focal signal abnormality (white arrow, A) within
calcaneus.
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Fig. 2B —18-year-old male basketball player with history of multiple
ankle sprains. Fast spin-echo T2-weighted (TR/TE, 4,000/70) sagittal
(A), axial (B), and coronal (C) MR images of ankle show
medium-sized focal signal abnormality (white arrow, A) within
calcaneus.
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Fig. 2C —18-year-old male basketball player with history of multiple
ankle sprains. Fast spin-echo T2-weighted (TR/TE, 4,000/70) sagittal
(A), axial (B), and coronal (C) MR images of ankle show
medium-sized focal signal abnormality (white arrow, A) within
calcaneus.
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Fig. 3 —16-year-old female volleyball player with chronic ankle pain.
Fast spin-echo T2-weighted (TR/TE, 4,000/70) sagittal MR image of ankle shows
small-sized focal signal abnormality (white arrow) within
calcaneus.
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No correlation between the age of the patient and the size of the focal
signal was found. All three sizes of lesions were identified in each of the
following age groups: < 30, 31-50, and 51-75 years. Age was found not to be
a useful predictive factor as to whether a patient's calcaneus would contain
this focus of signal. The majority of patients in all three age groups
contained this focus of increased T2 and decreased T1 signal. Seventy-five
percent of patients younger than 30 years, 61% of patients 31-50 years, and
88% of patients older than 50 years contained this focus of signal.
Of the five patients who underwent bilateral examinations, three had
bilateral lesions and two patients had negative findings bilaterally. The size
of the focus of increased T2 signal in the contralateral ankle varied in size
category in two of the three patients who underwent bilateral
examinations.
The bilateral ankles of two cadavers were imaged and all four ankles were
shown to contain this focus of increased T2 signal within the calcaneus. The
ankle containing the largest focus of increased T2 signal from each cadaver
was examined by pathology. Histologic examination of the cadaveric specimens
revealed thinned cortical bone surrounded by fatty marrow and numerous dilated
vascular channels consistent with prominent vascular remnants (Figs.
4A,
4B, and
4C).
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Fig. 4A —Histologic examination of cadaveric specimens. Sagittal fast
spin-echo T2-weighted (TR/TE, 4,000/67.3) MR image (A) through
cadaveric calcaneus shows medium-sized focal subtalar signal abnormality
(arrow), with corresponding gross specimen (B) and histologic
correlates (C). Arrows show corresponding dilated vascular channels
within histopathologic section.
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Fig. 4B —Histologic examination of cadaveric specimens. Sagittal fast
spin-echo T2-weighted (TR/TE, 4,000/67.3) MR image (A) through
cadaveric calcaneus shows medium-sized focal subtalar signal abnormality
(arrow), with corresponding gross specimen (B) and histologic
correlates (C). Arrows show corresponding dilated vascular channels
within histopathologic section.
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Fig. 4C —Histologic examination of cadaveric specimens. Sagittal fast
spin-echo T2-weighted (TR/TE, 4,000/67.3) MR image (A) through
cadaveric calcaneus shows medium-sized focal subtalar signal abnormality
(arrow), with corresponding gross specimen (B) and histologic
correlates (C). Arrows show corresponding dilated vascular channels
within histopathologic section.
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Discussion
A characteristic subtalar focus of signal within the calcaneus is
frequently seen on MRI of the ankle. This focus of signal has a characteristic
location near the insertion of the cervical and interosseous ligaments and
manifests as increased T2 and decreased T1 signal. We believe that through
cadaveric correlation, we have shown this to be a benign finding consistent
with prominent vascular remnants. This characteristic focal signal abnormality
within the calcaneus should not be confused with significant pathology and
should not be biopsied.
The calcaneus is infrequently a site for pathology. Although any lesion can
occur in the calcaneus, lesions frequently mentioned as occurring include
unicameral bone cyst, intraosseous lipoma, chondroblastoma, fractures,
infection, and metastatic disease. None of these would be expected to have the
appearance of the entity we have described in this report. A subtalar
subchondral cyst could have a similar appearance but would not be found in the
location of this process—that is, it should be subarticular.
Although calcaneal vascularity has been well documented, we were unable to
find any reference to vessels in the region of the calcaneus that have this
characteristic focus of signal. Vascular mapping studies have shown that the
intraosseous blood supply to the calcaneus is divided equally between medial
and lateral blood vessels [4,
5]. This arrangement produces a
watershed zone in the midline of the bone. Approximately 45% of the blood
supply comes from medial arteries, 45% from lateral arteries, and 10% from the
sinus tarsi artery [4,
5]. The 1-mm lateral calcaneal
artery is the main lateral intraosseous blood supplier
[4,
5]. It has been reported as a
branch of both the anterior and posterior tibial arteries and penetrates the
bone approximately 2 cm below the posterior joint space after an extraosseous
anastomosis with the lateral tarsal artery, which is a branch of the dorsalis
pedis artery [4,
5]. The lateral calcaneal
artery ramifies intraosseously and proceeds to the midline of the posterior
process, corpus, and posterior joint space
[4]. Small branches are also
given off to the anterior process
[4]. More than one penetrating
vessel is usually present medially. Several short branches from the lateral
plantar artery penetrate the bone immediately below the sustentaculum
[4]. The lateral plantar artery
is a branch of the posterior tibial artery
[4]. The sinus tarsi artery is
a large artery that runs through the sinus tarsi; however, its circulation
predominately enters the talus and not the calcaneus. Only a few small
arterioles have been shown to penetrate into the calcaneus
[4].
A limitation of our study is the small number of cadavers sampled; however,
given this limitation, it is notable that all four cadaveric ankles imaged
contained this lesion. None of our ankles were imaged after gadolinium
injection because that is not part of our routine ankle protocol. Selection
bias could be present in our patient population given that our patients were
not asymptomatic. In our series, no patient had pain referable to this
described subtalar location.
In conclusion, we have described a frequently seen focus of signal within
the calcaneus that on cadaveric pathologic correlation is consistent with
vascular remnants. Imaging characteristics of this abnormality are concordant
with the pathologic findings.
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Abstract
Introduction
