Musculoskeletal Imaging
Effect of Chondrocalcinosis on the MR Imaging of Knee Menisci
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OBJECTIVE. Our goal was to determine the influence of chondrocalcinosis on MR imaging in the detection of meniscal tears.
MATERIALS AND METHODS. A retrospective review was performed of knee MR imaging and arthroscopy records from two university hospitals between 1996 and 1998. Seventy individuals had radiographic evidence of chondrocalcinosis and underwent knee MR imaging. Thirty-seven of these individuals had undergone arthroscopy for further evaluation of their symptoms. MR imaging sensitivity and specificity in the detection of medial and lateral meniscal tears were calculated in these 37 patients who had radiographic evidence of chondrocalcinosis and in a control group of 34 patients who underwent MR imaging and arthroscopy but did not have knee chondrocalcinosis.
RESULTS. In the chondrocalcinosis group, MR imaging sensitivity, specificity, and accuracy for meniscal tear were 78%, 71%, and 78%, respectively, for the lateral meniscus, and 89%, 72%, and 81% for the medial meniscus. The control group showed sensitivity, specificity, and accuracy of 93%, 100%, and 97%, respectively, for the lateral meniscus and 100% in all cases for the medial meniscus. The MR imaging detection of meniscal tears in both the lateral and medial compartments combined is significantly poorer in the presence of chondrocalcinosis (p < 0.005).
CONCLUSION. MR imaging sensitivity and specificity for detection of meniscal tear is decreased in the presence of meniscal chondrocalcinosis. Chondrocalcinosis appeared as a high-signal-intensity region on T1-weighted, intermediate-weighted, and inversion recovery sequences. The high signal of chondrocalcinosis on inversion recovery sequence is an interesting observation that to our knowledge has not been previously reported. Radiographic correlation with the MR imaging examination can help prevent overdiagnosing meniscal tears.
| Introduction |   |
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Chondrocalcinosis refers to the calcification in the menisci or articular cartilage due to the deposition of calcium pyrophosphate dihydrate crystal, dicalcium phosphate dihydrate, calcium hydroxyapatite crystals, or a combination of these [1, 2]. Calcium pyrophosphate dihydrate crystal deposition disease is the most common crystalline arthropathy [3]. Intraarticular crystals were first described as weakly positive birefringent nonurate crystals at polarized light microscopy in the joint fluid of patients who had goutlike arthritis attacks [4, 5]. Zitnan and Sitaj [6] first described the radiographic manifestations of this entity, coining the term “chondrocalcinosis polyarticularis.” Punctate or linear intraarticular calcifications are seen on the radiographs in classic calcium pyrophosphate dihydrate crystal deposition disease [7]. According to Yang et al. [8], meniscal calcifications are more frequent than hyaline cartilage calcifications, and meniscal calcifications are considerably more prevalent in men.
Radiographic characteristics of chondrocalcinosis are well known [9]. However, descriptions of the MR appearance of meniscal chondrocalcinosis have been limited [10]; and to our knowledge, no MR arthroscopic correlation study has been reported. Articular cartilage calcifications as seen on MR imaging and arthroscopy were evaluated by Beltran et al. [11]. However, no meniscal signal abnormality was noted in that study. The purpose of our study was to determine whether the presence of radiographically detectable calcification has an effect on MR imaging in the diagnosis of meniscal tear.
| Materials and Methods | |
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A retrospective review of medical records from two university hospitals for a 2-year period (1996-1998) identified 70 patients with radiographic evidence of chondrocalcinosis who had undergone knee MR imaging within 6 months of the radiographs. Knee pain was the most common indication for these examinations. Of these patients, 37 (22 men and 15 women; 74 total menisci) underwent arthroscopic examinations within 1 month of MR imaging; these patients formed our study group. Their age range was 26-86 years (mean age, 48 years). Our control group consisted of 34 patients (20 men and 14 women; 68 total menisci) without radiographic evidence of chondrocalcinosis. These patients (age range, 28-79 years; mean age, 45 years) had undergone knee MR imaging and arthroscopy for evaluation of knee pain and suspected internal derangement during the same time (1996-1998). MR imaging interpretations were performed prospectively by radiologists trained in musculoskeletal radiology. A clinical review of the MR imaging and arthroscopy reports was performed in each group.
MR images were obtained with a 1.5-T system (General Electric Medical Systems, Milwaukee, WI) with an extremity coil. The following imaging sequences were acquired: sagittal and axial spin-echo T1-weighted (TR range/TE range, 400-750/15-20; matrix size, 256 × 192), intermediate-weighted (1800-3500/19-40; matrix size, 256 × 192), T2-weighted (2500-3500/60-80), and inversion recovery (TR/TE, 4000/26 [approximately]; inversion time, 180 msec; matrix size, 256 × 192) sequences were obtained in 20 patients. The evaluation of meniscal tear was based on T1-weighted, intermediate-weighted, and T2-weighted sequences.
A cross-tabulation of MR imaging and arthroscopic findings was made for each knee compartment (37 medial and 37 lateral). A meniscal tear was defined as a linear region of increased signal within a meniscus communicating with one of the articular surfaces on more than one image [12,13,14].
T1-weighted coronal, intermediate-weighted, and T2-weighted spin-echo sagittal images were used for meniscal assessment. Additional coronal inversion recovery images were also reviewed (available in 20 patients) but were not used primarily for the detection of meniscal tears. Correlation was made with the presence and location of chondrocalcinosis on anteroposterior and lateral knee radiographs to document whether the abnormal meniscal signal (tear) occurred in the area of chondrocalcinosis. The sensitivity, specificity, and accuracy of MR imaging to discover meniscal tears were calculated for each compartment in the chondrocalcinosis and control groups.
| Results | |
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Of the original 70 patients with meniscal calcification, none showed articular calcifications on radiographs or MR imaging. As shown in Tables 1 and 2, the accuracy for the MR imaging detection of meniscal tears in the chondrocalcinosis patients was significantly lower than in the control group (p < 0.005). As shown in Table 3, only one misdiagnosis occurred—a false-negative lateral meniscal tear in the control group. The patient was among the six judged by arthroscopy to have medial and lateral tears. MR imaging correctly identified the 19 control patients with medial meniscal tears and the nine with lateral meniscal tears.
In the chondrocalcinosis group, two patients had medial and lateral tears as shown on arthroscopy. All four tears were missed on MR imaging (false-negative). Sixteen patients had a medial tear only. None of these were missed on MR imaging. Seven patients had a lateral tear only. None of these were missed on MR imaging. Among the 37 patients, 12 did not have a tear (as judged by arthroscopy). All 12 of these were misdiagnosed (false-positive) on MR imaging. These tears were equally divided between medial and lateral compartments. In summary, 14 (38%) of the 37 patients with chondrocalcinosis were misdiagnosed by MR imaging. The 95% confidence limit for this proportion is 22-55%.
The accuracy of MR imaging in the detection of meniscal tears in patients with chondrocalcinosis is 23 (62%) of 37, with 95% confidence limits of 45-78%.
Individuals with chondrocalcinosis and meniscal tear on arthroscopy showed a hyperintense intermediate-weighted, T1-weighted, and T2-weighted inversion recovery intrameniscal signal, always extending to at least one articular surface. Individuals with chondrocalcinosis (Fig. 1A) and false-positive meniscal tear (positive MR imaging, negative arthroscopy) showed similar meniscal signal abnormalities (Figs. 1B, 1C, and 1D), as described earlier, reaching to at least one articular surface. Of the false-positive meniscal tears, only one showed arthroscopic evidence of minimal fraying. The presence of chondrocalcinosis was seen on a knee radiograph (Fig. 2A) in another patient with false-positive meniscal tear (positive MR imaging, negative arthroscopy). The MR imaging was compatible with a lateral meniscal tear (Figs. 2B, 2C, and 2D). Hyperintense meniscal signal was noted on T2-weighted (Fig. 2E) and inversion recovery (Fig. 2F) sequences. No meniscal tear was detected on arthroscopy.
 View larger version (162K) | Fig. 1A. —48-year-old man who presented with knee pain. Anteroposterior knee radiograph shows heavy meniscal calcifications in lateral meniscus (arrow). |
 View larger version (167K) | Fig. 1B. —48-year-old man who presented with knee pain. Sagittal T1-weighted spin-echo MR image (TR/TE, 500/20) shows high signal intensity in lateral meniscus with extension to superior articular surface (anterior horn) and inferior articular surface (posterior horn), interpreted as meniscal tear (arrows). No meniscal tear was found on arthroscopy. |
 View larger version (89K) | Fig. 1C. —48-year-old man who presented with knee pain. Coronal T1-weighted spin-echo MR image (550/20) shows central high-signal-intensity region in lateral meniscus (arrow) extending to inferior articular surface, suggestive of meniscal tear. |
 View larger version (89K) | Fig. 1D. —48-year-old man who presented with knee pain. Sagittal intermediate-weighted MR image (2166/20) shows abnormal meniscal signal (arrow) identical to that seen in C. |
 View larger version (201K) | Fig. 2A. —64-year-old man who was evaluated for knee pain. Anteroposterior knee radiograph shows significant lateral meniscal calcifications (arrow). Moderate medial compartment osteoarthritis is also seen. |
 View larger version (127K) | Fig. 2B. —64-year-old man who was evaluated for knee pain. Coronal T1-weighted MR image (TR/TE, 550/20) shows high signal intensity in lateral meniscus (arrow). |
 View larger version (229K) | Fig. 2C. —64-year-old man who was evaluated for knee pain. Sagittal intermediate-weighted MR image (2300/20) shows high-signal-intensity region in lateral meniscus body extending to inferior articular surface (arrow). |
 View larger version (205K) | Fig. 2D. —64-year-old man who was evaluated for knee pain. Sagittal intermediate-weighted MR image (2300/20) shows high signal intensity in lateral meniscus posterior horn extending to superior articular surface (arrow). |
 View larger version (265K) | Fig. 2E. —64-year-old man who was evaluated for knee pain. Sagittal T2-weighted MR image (2300/80) shows hyperintense signal in lateral meniscus posterior horn (arrow) corresponding to abnormalities in A-D. |
 View larger version (190K) | Fig. 2F. —64-year-old man who was evaluated for knee pain. Coronal inversion recovery MR image (4250/19; inversion time, 180 msec) shows high-signal-intensity area in lateral meniscus (arrow). |
| Discussion | |
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The prevalence of chondrocalcinosis is reported to be 5.0-14.6% and increases with age [15, 16]. In one study [15], chondrocalcinosis was seen on radiographs in 9.6% of patients 50 years old or older. In Spain, Sanmarti et al. [16] reported an estimated prevalence of chondrocalcinosis of 10%. Yang et al. [8] found meniscal calcifications to be more frequent than hyaline cartilage calcifications. A multitude of conditions and mechanisms are implicated in the pathogenesis of chondrocalcinosis [17, 18]. In our patients, the radiographic appearance of meniscal calcification was the same regardless of the causes of the chondrocalcinosis.
Our results show decreased sensitivity, specificity, and accuracy of MR imaging for diagnosing meniscal tear in the presence of chondrocalcinosis. Twelve (32%) of the 37 patients with radiographic evidence of chondrocalcinosis had an MR imaging diagnosis of meniscal tear that was not confirmed at arthroscopy. No false-positive tears were found in the control group of patients without chondrocalcinosis. An increased number of false-positives for meniscal tear in the chondrocalcinosis group resulted from the MR imaging appearance of high meniscal signal reaching the articular surface.
Confirmed meniscal tears were more common in the medial meniscus [19]. However, this may be a result of the small number of lateral meniscal tears. Although the total number of false-negative meniscal tears was lower than false-positive meniscal tears in the chondrocalcinosis group, a false-negative MR imaging result for meniscal tear has more serious implications than a false-positive result. It is possible that a large area of meniscal signal abnormality as a result of chondrocalcinosis decreases the sensitivity to detect abnormal signal extension to the meniscal surface, thus obscuring the diagnosis of a meniscal tear on MR imaging in false-negative cases. The diagnostic accuracy of MR imaging for meniscal tears in both compartments (medial and lateral) was affected by the presence of chondrocalcinosis. MR imaging sensitivity and specificity for meniscal tear detection in the control group were within the previously reported range [20].
Although calcifications are typically of low signal on all MR imaging pulse sequences, descriptions of high-signal-intensity calcium deposits in the brain [21, 22] and lumbar intervertebral disks [23] have been reported. Beltran et al. [11] described articular cartilage calcifications on spin-echo intermediate-weighted, T2-weighted, inversion recovery, and T2-weighted gradient-recalled echo sequences as hypointense foci with a surrounding hyperintense halo, thought to be a result of magnetic susceptibility artifact. No meniscal calcifications were noted in that study. In another report [9], a hyperintense meniscal signal abnormality on intermediate-weighted, T1-weighted, and T2-weighted sequences in a patient with chondrocalcinosis, initially suspected to be a meniscal tear, was not found on subsequent arthroscopy. Eustace et al. [24] described linear high signal intensity in the meniscus on MR imaging in a patient with hemochromatosis and radiographic evidence of chondrocalcinosis. However, in this patient, the abnormal meniscal signal did not extend to the articular surface. Only one previous abstract [25] has reported high intrameniscal T2-weighted spin-echo signal in the presence of chondrocalcinosis.
No single theory has satisfactorily explained the cause of high signal intensity related to calcifications on certain MR imaging sequences. Increased T1- and T2-weighted MR imaging intervertebral disk signal in the presence of calcifications on radiography has been thought to be caused by the concentration of the calcium crystals [21]. Henkelman et al. [22] found high MR imaging signal on T1-weighted images to be associated with T1 shortening due to calcified crystals.
In our study, high intrameniscal inversion recovery signal (Figs. 1E and 2F) corresponded to the hyperintense intermediate-weighted, T1-weighted, and T2-weighted meniscal signal in individuals with radiographic evidence of chondrocalcinosis. It did not show the “halo” type of hyperintense signal that has been described previously in the literature [11].
 View larger version (187K) | Fig. 1E. —48-year-old man who presented with knee pain. Coronal inversion recovery MR image (4250/19; inversion time, 180 msec) shows central high-signal-intensity area in lateral meniscus (arrow), corresponding to high signal in figures B and C, and chondrocalcinosis in A. |
Our results show the confounding effect that chondrocalcinosis has on the MR imaging diagnosis of meniscal tear. These results reinforce the need for correlation of MR imaging with radiography to avoid errors in diagnosing meniscal tears. Radiologists must be aware of this potential pitfall and know that they can benefit from radiographic correlation.
Address correspondence to S. Kaushik.
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