AJR 2002; 179:645-648
© American Roentgen Ray Society
Grade 2C Signal in the Mensicus on MR Imaging of the Knee
Thomas R. McCauley1,
Won-Hee Jee1,2,
Marc T. Galloway3,4,
Kevin Lynch3 and
Peter Jokl3
1 Department of Diagnostic Radiology, Yale University School of Medicine, 333
Cedar St., Rm. MRC 147, New Haven, CT 06520.
2 Present address: Department of Radiology, Kangnam St. Mary's Hospital, The
Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, South Korea
137-701.
3 Department of Orthopedic Surgery, Yale University School of Medicine, New
Haven, CT 06520.
4 Present address: Cincinnati Sports Medicine and Orthopedic Center, 12115
Sheraton Ln., Cincinnati, OH 45246.
Received July 20, 2001;
accepted after revision February 28, 2002.
Address correspondence to T. R. McCauley.
Abstract
OBJECTIVE. The objective of our study was to evaluate the clinical
significance of grade 2C mensical signal (an extensive triangular or
wedge-shaped signal that does not reach the surface on more than one image) on
MR imaging of the knee.
MATERIALS AND METHODS. Review of 1106 MR imaging reports over 2
years revealed 88 patients with menisci described as containing triangular,
wedge-shaped, extensive, or grade 2C signal. Image review by consensus of two
radiologists found 34 menisci in 29 patients that fit criteria for grade 2C
signal. Seven menisci containing grade 2C signal were evaluated with
arthroscopy. An additional three patients with grade 2C meniscal signal with
arthroscopic correlation were identified from 4 previous years.
RESULTS. Prevalence of grade 2C signal was 1.5% (34/2212 menisci).
Seven (21%) of these 34 menisci had subsequent arthroscopy and three of these
had meniscal tears. Including the three additional menisci with grade 2C
signal from 4 previous years, five (50%) of 10 menisci with grade 2C signal
were torn at arthroscopy. No difference was noted between torn and intact
menisci in the number of images with grade 2C signal. In patients with tears,
the range was three to 10 images (mean, 6.6 images) compared with a range of
two to 10 images (mean, 6.6 images) in patients without tears. The maximal
percentage of area of abnormal signal in patients with tears ranged from 70%
to 90% (mean, 80%) compared with a range of 60-90% (mean, 82%) in patients
without tears. The patient age range was 23-64 years (mean, 47 years) in
patients with tears and 16-67 years (mean, 47 years) in patients without
tears.
CONCLUSION. Grade 2C meniscal signal has a low incidence. Although
half of patients with symptoms meriting arthroscopy have tears, most patients
with grade 2C signal are not treated with arthroscopy.
Introduction
Extensive triangular or wedge-shaped meniscal abnormalities that do not
reach criteria for tear (grade 2C signal)
[1] are sometimes encountered
on MR imaging of the knee. A previous report
[1] of patients with
arthroscopic correlation found tears in three of five menisci with grade 2C
signal.
The purpose of this study was to evaluate the clinical significance of
grade 2C signal in the meniscus on MR imaging of the knee. We determined the
prevalence of grade 2C signal in menisci of patients undergoing MR imaging of
the knee, the number of these patients who required arthroscopic treatment,
and the prevalence of tears in patients who undergo arthroscopy.
Materials and Methods
We obtained approval for our study from the institutional human
investigation committee. Review of 1106 MR imaging reports for patients
referred by nine sports medicine specialists during a 2-year period revealed
88 patients with menisci described as containing triangular, wedge-shaped,
extensive, or grade 2C signal in a meniscus. MR imaging was performed with a
1.5-T imager (Signa Advantage; General Electric Medical Systems, Milwaukee,
WI) with a transmit-receive extremity coil or a receive-only phased array
extremity coil (General Electric Medical Systems).
We used three imaging sequences. Transverse fat-suppressed fast spin-echo
intermediate-weighted images were obtained with the following parameters: TR
range/TEeff, 3000-4500/20; section thickness, 4 mm; gap, 0.5 mm;
field of view, 16 cm; matrix, 256 x 256; 1 excitation; and echo-train
length, 10. Sagittal T1-weighted spin-echo images were acquired with
450-600/14; section thickness, 3.3 mm; no gap; field of view, 16 cm; matrix,
256 x 192; and 1 excitation. Coronal double-echo fast spin-echo images
were obtained with the parameters of TR range/first-echo TEeff,
second-echo TEeff, 3000-4500/20, 80; section thickness, 3.3 mm;
gap, 0.3 mm; field of view, 14 cm; matrix, 256 x 256; 1 excitation; and
echo-train length, 10 (effective echo-train length, 5 for each echo).
Meniscal windows (photographed with a narrow window width
[2] from the sagittal
T1-weighted series and from the coronal first-echo images were reviewed. For
each clinical case, the window and level were chosen by the technologist. The
window width was set to one and the level was chosen so that menisci were
depicted as black and fat as white. The window was then broadened until the
trabeculae in the bone marrow were visible. The sagittal and coronal images
were reviewed for the presence of grade 2C signal by consensus of two
experienced musculoskeletal radiologists unaware of arthroscopic results. The
criteria we used for grade 2C signal were triangular or wedge-shaped high
signal in the meniscal substance making up at least 50% of the cross-sectional
area that does not reach an articular surface on more than one image
[1,
3] (Fig.
1A,1B).
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Fig. 1B. —16-year-old girl with knee pain after falling and normal
menisci at arthroscopy. Sagittal T1-weighted spin-echo MR image shows grade 2C
signal in posterior horn of medial meniscus (arrow).
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Fifty-four of the 88 patients whose MR imaging studies were reviewed on the
basis of clinical reports were found not to have grade 2C signal—either
because they met criteria for tear (n = 18) or because their internal
meniscal signal was not triangular or wedge-shaped or did not make up 50% of
the cross-sectional area (n = 36). For the remaining 34 menisci
identified as showing grade 2C signal (29 patients), the reviewers examined
the following MR imaging features to determine whether any of these allowed
discrimination between torn and intact menisci: location, maximal percentage
of area of abnormal signal (in increments of 10%), presence of high signal
extending to meniscal surface on one image, and number of images having grade
2C signal (total of both coronal and sagittal images). Tears elsewhere in the
menisci and in the anterior cruciate ligament were also noted.
The 29 patients with grade 2C meniscal signal were followed from 12 to 33
months (mean, 19 months), and seven menisci in five patients were subsequently
evaluated with arthroscopy. Arthroscopy was performed when knee pain was
present at the site of grade 2C signal or when meniscal tear was found
elsewhere in the knee. An additional 26 patients were identified from the
previous 4 years whose menisci were described as containing triangular,
wedge-shaped, extensive, or grade 2C signal and who underwent arthroscopic
follow-up. At review, three of these menisci in three patients fit criteria
for grade 2C signal; these images were also reviewed for the MR imaging
features described. Because the orthopedic charts and clinical follow-up were
not available for most of the patients from the earlier 4-year period, this
group was not included in the analysis to determine the proportion of patients
with grade 2C signal who underwent arthroscopic treatment.
We identified nine patients with 10 menisci containing grade 2C signal with
arthroscopic correlation. These patients included six males and three females
with ages ranging from 16 to 67 years (mean age, 47 years), in whom we studied
six left and three right knees. None of the patients had previously undergone
knee surgery. The delay between MR imaging and arthroscopy ranged from 4 to
264 days; the average delay was 99 days. The arthroscopic reports were
reviewed to determine the location and configuration of meniscal tear, the
presence of anterior cruciate ligament tear, and the presence of
osteoarthritis. Comparisons between menisci with and without tears were
performed using a two-tailed unpaired t test for the number of images
with grade 2C signal, the maximal percentage of area of abnormal signal, and
patient age. We used the Fisher's exact test for the number of menisci with
signal extending to the surface on one image.
Results
Grade 2C signal was present in 34 (1.5%) of 2212 menisci evaluated with MR
imaging over a 2-year period. The 34 menisci with grade 2C signal were
identified in 29 patients. Seven (21%) of these 34 menisci had subsequent
arthroscopy and three (9%) had meniscal tears. Surgery was not performed in
patients with no symptoms at the site of grade 2C signal except in four
patients who had a tear in the opposite meniscus. Two of the three menisci
identified over the 4 previous years as having grade 2C signal and
arthroscopic correlation showed tears (Fig.
2). Thus, five (50%) of 10 menisci with grade 2C signal evaluated
with arthroscopy had tears. Among the five meniscal tears, grade 2C signal was
identified in the posterior horn of the medial meniscus (n = 3) and
in the posterior horn of the lateral meniscus (n = 2). Among the five
intact menisci, signal abnormality was identified in the posterior horn of the
medial menisci (n = 2, Figs.
1A,1B
and 3), the posterior horn of
the lateral meniscus (n = 2), and the body of the lateral meniscus
(n = 1) (Table 1).
Excluding one meniscus whose tear configuration was not described on the
arthroscopic report, all meniscal tears in menisci with grade 2C signal were
degenerative horizontal tears. In patients with grade 2C signal, the examined
imaging features for those with and without tear at arthroscopy were similar
(Student's t test and Fisher's exact test). We examined the following
features in patients with and without tear, respectively: number of images
having grade 2C signal (range, three to 10 images and mean, 6.6 images; vs
range, two to 10 images and mean, 6.6 images); maximal percentage of area of
abnormal signal on the image with the largest signal abnormality (range,
70-90% and mean, 80%; vs range, 60-90% and mean, 82%); and number of patients
with signal extending to the surface on one image (2/5 vs 1/4). Patient age
was also comparable between the two groups; in patients with tear, the range
was 23-64 years (mean, 47 years), and in patients without tear the range was
16-67 years (mean, 47 years). Osteoarthritis was described at arthroscopy in
four of five patients with tears versus three of five patients without tears.
No patient had concurrent anterior cruciate ligament tear. Four patients with
grade 2C signal who underwent arthroscopy had pain at the site of a tear in
the opposite meniscus and no pain on the side of the knee with grade 2C
signal. Two of these four patients had meniscal tear at the site of grade 2C
signal despite the absence of pain.
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Fig. 2. —Sagittal T1-weighted spin-echo MR image in 49-year-old man
with knee pain on exercise shows grade 2C signal in posterior horn of lateral
meniscus (arrow), confirmed as tear at arthroscopy.
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Fig. 3. —Sagittal T1-weighted spin-echo MR image in 58-year-old woman
with chronic knee pain and swelling shows grade 2C signal in posterior horn of
medial meniscus (arrow), confirmed as intact meniscus at
arthroscopy.
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Discussion
Dillon et al. [1] found
meniscal tears in three of five patients with grade 2C signal on MR imaging.
Their study did not investigate the prevalence of grade 2C signal in patients
undergoing MR imaging or the percentage of patients with grade 2C signal on MR
imaging who undergo subsequent arthroscopy. We found that grade 2C signal has
a low prevalence in patients undergoing MR imaging of the knee, occurring in
3% of patients. Most patients with grade 2C signal are not treated with
arthroscopy because they do not have symptoms referable to the site of
abnormality. Of patients who have subsequent arthroscopy, we found that half
have tears, similar to the 60% prevalence (3/5) found previously
[1]. In our study, grade 2C
signal was most commonly observed in the posterior horn of the meniscus
(Table 1). The high prevalence
of grade 2C signal in the posterior horn is similar to that found for grade 2
signal in previous reports [4,
5], but it is contradictory to
another study that most frequently found grade 2 signal in the anterior horn
and body segment [6].
In our study, all four meniscal tears with tear configuration described in
the arthroscopic reports were degenerative horizontal tears, and
osteoarthritis was present in 78%. This finding is consistent with a previous
report that the coincidence of horizontal tears and osteoarthritis is frequent
[7]. Grade 2 meniscal
abnormality has been described as corresponding to mucinous degeneration and
is commonly found with eosinophilic degeneration, scarring, or meniscal
calcification at pathology
[5,6,7,8].
Our results indicate that grade 2C signal might represent more extensive
degeneration that can be associated with or progress to degenerative tear. We
were not able to evaluate the untorn menisci having grade 2C signal to
determine whether these menisci have internal degeneration. Although the
association of grade 2C signal with osteoarthritis and degenerative tears
might suggest that older patients are more likely to have tears associated
with grade 2C signal, we found that patients with grade 2C meniscal signal who
had tears were of similar age to those who did not have tears. Our youngest
patient in whom a tear was found at the site of grade 2C signal was a 22
year-old man; subsequent to this study, we performed MR imaging in a
17-year-old boy who was found to have a meniscal tear at the site of grade 2C
signal. Thus, grade 2C signal can be associated with tear even in relatively
young patients. Increased signal has been described in the medial portion of
the posterior horn of the lateral meniscus because of the magic angle effect
[9]. The interpreters of the
clinical MR images and the two radiologists performing retrospective review
were aware of this artifact. Therefore, these observers classified signal in
the posterior horn of the lateral meniscus as grade 2C only if it was more
extensive or more intense than usually occurs as a result of the magic angle
effect.
We included in our categorization of grade 2C signal those menisci having
signal extending to the surface on one image. We decided to do so on the basis
of two studies: one that showed no meniscal tears in six menisci with linear
signal contacting the surface on one image only
[1] and another that reported
only 55% of medial and 30% of lateral menisci are torn when signal contacts
the surface on one image [10].
Excluding patients with signal extending to the surface on one image only,
tears were present in three of seven patients with grade 2C signal, a finding
that is similar to the 50% prevalence we found for all patients with grade 2C
signal.
Limitations of our study include the small sample sizes. We could not
collect larger samples because of the low prevalence of grade 2C signal in
menisci and the small number of patients with grade 2C signal who undergo
arthroscopic evaluation. We do not know if a similar prevalence of tear occurs
in patients with grade 2C signal who do not have symptoms warranting
arthroscopy. We routinely use narrow window width settings for meniscal
evaluation at our institution; it is possible that grade 2C signal would be
less frequently diagnosed when using routine window widths. The relatively
long interval between MR imaging and arthroscopy in this study occurred
because orthopedic surgeons at our institution often attempt conservative
management before considering arthroscopy when grade 2C signal is found. We do
not know whether tears were present but not visible at the time of MR imaging
or whether tears developed in the period between MR imaging and
arthroscopy.
In conclusion, we found that half of the patients with grade 2C meniscal
signal and symptoms warranting arthroscopic follow-up have tears. Most
patients with grade 2C meniscal signal are not treated with arthroscopy
because they do not have symptoms at the site of grade 2C signal. Thus, when
grade 2C signal is seen on MR imaging, arthroscopic follow-up is indicated if
symptoms referable to the site of abnormal signal are also present. We could
not identify imaging features that followed discrimination of torn from intact
menisci containing grade 2C signal.
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Abstract
Introduction
