Oblique meniscomeniscal ligament: another potential pitfall for a meniscal tear--anatomic description and appearance at MR imaging in three cases

Magnetic resonance imaging of the knee

Knee pain is frequently seen in patients of all ages, with a wide range of possible aetiologies. Magnetic resonance imaging (MRI) of the knee is a common diagnostic examination performed for detecting and characterising acute and chronic internal derangement injuries of the knee and helps guide patient management. This article reviews the current clinical practice of MRI evaluation and interpretation of meniscal, ligamentous, cartilaginous, and synovial disorders within the knee that are commonly encountered.

Magnetic resonance imaging of the meniscal roots

The meniscal roots and supporting structures anchor the menisci to the tibial plateau and resist hoop stress, thereby preventing radial displacement of the menisci and secondary degenerative tibiofemoral compartment changes that may occur if this is compromised. The anatomy of the four meniscal roots and their supporting structures on magnetic resonance imaging (MRI) will be outlined in this review article, as well as the imaging appearances of meniscal root-related pathology, namely meniscal root degeneration and tears, meniscal extrusion and tibial plateau cystic lesions.

The Meniscofemoral Ligament Mimicking a Lateral Meniscus Tear

A 58-year-old male patient who had developed left knee pain with a history of trauma was referred to our hospital. Physical examination and further examination by magnetic resonance imaging revealed results that closely resemble a horizontal tear of the lateral meniscus and a tear of the medial meniscus. Arthroscopically, we found a cord-like structure originating from the posterior 1/3 portion of the lateral meniscus and passing obliquely toward the medial femoral condyle in front of the posterior cruciate ligament without a tear of the lateral meniscus. In this report, we describe a rare case of anterior meniscofemoral ligament that was clearly seen on arthroscopy and mimicked a meniscal tear, which is also known as a pseudo-tear of the meniscus.

Clinics in diagnostic imaging (177). Medical meniscus bucket-handle tear with medial oblique meniscomeniscal ligament

A 29-year-old man with a previous football injury to his left knee presented with pain of the same knee. The patient twisted it as he was turning a corner quickly while going up the stairs, leading to internal rotation of his femur on his tibia with his knee in flexion. MR imaging revealed a bucket-handle tear of the medial meniscus, as well as a complete tear of the anterior cruciate ligament. However, image interpretation was complicated by the presence of a medial oblique meniscomeniscal ligament, a rare normal variant among intermeniscal ligaments of the knee. All four recognised variants of intermeniscal ligaments are discussed, with emphasis on their prevalence, imaging and anatomical features, and the way in which they may mimic meniscal tears.

It's not what it looks like: challenges in diagnosis of synovial lesions of the knee joint

BACKGROUND

With the advent of MRI (Magnetic Resonance Imaging), Synovial lesions around knee are being more and more easily detected. Synovial lesions of knee present with boggy swelling, effusion, pain, and restriction of motion. Differential diagnoses of such lesions include pigmented villonodular synovitis, synovial lipoma, synovial chondromatosis, rheumatoid arthritis, synovial hemangioma, amyloid arthropathy, xanthomata and lipoma arborescens. CT and MRI often help in diagnosis of such lesions. MRI of Lipoma Arborescens has been regarded to have characteristic diagnostic appearance - it includes a synovial mass with frond-like architecture and fat signal intensity on all pulse sequences. Sometimes Lipoma Arborescens can present in conjunction with inflammatory arthritis. Synovectomy is often curative for such conditions.

FINDINGS

We report two cases where lesions diagnosed as Lipoma Arborescens on MRI subsequently revealed to be chronic inflammatory synovitis, characterized by absence of fat infiltration in histopathological examination - refuting the original diagnosis. There was infiltration of lymphocytes and neutrophils in the synovium, suggestive of chronic inflammatory arthritis. Both of these patients required management from rheumatologist, and had relief of symptoms after use of methotrexate and hydroxychloroquine. We also report a third case, where a loose body appearing as chondral fragment on arthroscopy was subsequently diagnosed as an organized hematoma on histopathological examination.

CONCLUSION

Diagnostic pitfalls after MRI of the knee is not uncommon. For example - normal variant of meniscomeniscal ligaments have been reported as meniscal tears; motion artifacts have been falsely reported as meniscal injuries; and meniscofemoral ligament can appear as free osteochondral fragment. In most of these cases, a routine arthroscopy is enough to clear the confusion. However, as evident in the three cases described here - in some synovial lesions of knee joint, even after MRI and arthroscopic examination, histopathological confirmation may still be prudent. In spite of availability of advanced imaging technologies and high definition arthroscopy equipment, an arthroscopy surgeon still must not forget the value of histopathological examination in establishing the true nature of synovial lesions of the knee joint.

Double PCL sign does not always indicate a bucket-handle tear of medial meniscus

The discoid medial meniscus is an extremely rare anomaly. Bilateral discoid medial menisci are much more rare but intermittently reported. We report the first case of bilateral discoid medial menisci with positive double PCL sign, which typically indicates a bucket-handle tear of medial meniscus. A literature review was also conducted on bilateral discoid medial menisci.

Reporting knee meniscal tears: technical aspects, typical pitfalls and how to avoid them

Magnetic resonance imaging (MRI) is the most accurate imaging technique in the diagnosis of meniscal lesions and represents a standard tool in knee evaluation. MRI plays a critical role in influencing the treatment decision and enables information that would obviate unnecessary surgery including diagnostic arthroscopy. An accurate interpretation of the knee depends on several factors, starting with technical aspects including radiofrequency coils, imaging protocol and magnetic field strength. The use of dedicated high-resolution orthopaedic coils with a different number of integrated elements is mandatory in order to ensure high homogeneity of the signal and high-resolution images. The clinical imaging protocol of the knee includes different MRI sequences with high-spatial resolution in all orientations: sagittal, coronal, and axial. Usually, the slice thickness is 3 mm or less, even with standard two-dimensional fast spin echo sequences. A common potential reason for pitfalls and errors of interpretation is the unawareness of the normal tibial attachments and capsular attachment of the menisci. Complete description of meniscal tears implies that the radiologist should be aware of the patterns and the complex classification of the lesions.

TEACHING POINTS

• Technical factors may influence MRI interpretation. • Unawareness of the normal meniscal anatomy may lead to errors of interpretation. • Description of meniscal tears implies the knowledge of meniscal tear classification.

MR imaging-based diagnosis and classification of meniscal tears

Magnetic resonance (MR) imaging is currently the modality of choice for detecting meniscal injuries and planning subsequent treatment. A thorough understanding of the imaging protocols, normal meniscal anatomy, surrounding anatomic structures, and anatomic variants and pitfalls is critical to ensure diagnostic accuracy and prevent unnecessary surgery. High-spatial-resolution imaging of the meniscus can be performed using fast spin-echo and three-dimensional MR imaging sequences. Normal anatomic structures that can mimic a tear include the meniscal ligament, meniscofemoral ligaments, popliteomeniscal fascicles, and meniscomeniscal ligament. Anatomic variants and pitfalls that can mimic a tear include discoid meniscus, meniscal flounce, a meniscal ossicle, and chondrocalcinosis. When a meniscal tear is identified, accurate description and classification of the tear pattern can guide the referring clinician in patient education and surgical planning. For example, longitudinal tears are often amenable to repair, whereas horizontal and radial tears may require partial meniscectomy. Tear patterns include horizontal, longitudinal, radial, root, complex, displaced, and bucket-handle tears. Occasionally, meniscal tears can be difficult to detect at imaging; however, secondary indirect signs, such as a parameniscal cyst, meniscal extrusion, or linear subchondral bone marrow edema, should increase the radiologist's suspicion for an underlying tear. Awareness of common diagnostic errors can ensure accurate diagnosis of meniscal tears. Online supplemental material is available for this article.

Normal anatomical variants of the menisci and cruciate ligaments that may mimic disease

There are many normal anatomical variants of the knee joint. Some are common and others are rare. With continuing improvements in the spatial resolution of MRI, smaller variants are more clearly demonstrated and can be mistaken for disease. They can all be differentiated from pathological conditions by understanding their anatomy and key differentiating features. This review compares normal variants of the menisci and cruciate ligaments with the pathological disorders that can mimic them.

Posterior root of lateral meniscus: the detailed anatomic description on 3T MRI

BACKGROUND

Although there have been some attempts to reveal the anatomy of the posterior root of the lateral meniscus (PRLM) through cadaver studies, arthroscopy, or imaging, it has not yet been described fully.

PURPOSE

To describe clearly the unique features of the PRLM, including its course, configuration, and size, using 3.0-T magnetic resonance imaging (MRI).

MATERIAL AND METHODS

A total of 105 knee 3.0-T MR examinations of 103 patients with arthroscopically proven intact PRLM were reviewed retrospectively. Based on fat-saturated, proton-density-weighted (PDW) axial/coronal images and PDW sagittal images, the course, configuration, and attachment sites of the PRLM were evaluated.

RESULTS

The majority of PRLM (76.2%) had two attachment sites: the medial tubercle along the intertubercular crest, just posteromedial to the tibial attachment of the anterior cruciate ligament (ACL), and the posterior slope of the lateral tubercle. The remaining cases (23.8%) had a solitary insertion on the intertubercular area (17 cases), or the posterior slope of the lateral tubercle (eight cases). The PRLM of the intertubercular area appeared as a dark signal line parallel to the tibial plateau on the mid-sagittal image and dark signal foci traversing the intertubercular crest on contiguous coronal images.

CONCLUSION

The PRLM inserts mainly in the intertubercular area with a thin, long anterior extension to the point just posteromedial to the tibial attachment of the ACL. It is well delineated on PDW 3.0-T MRI as a dark signal line parallel to the tibial plateau on mid-sagittal images and dark signal foci traversing the intertubercular crest on contiguous coronal images.

Magnetic resonance imaging of the knee

Context:

Magnetic resonance imaging (MRI) affords high-resolution visualization of the soft tissue structures (menisci, ligaments, cartilage, etc) and bone marrow of the knee.

Evidence Acquisition:

Pertinent clinical and research articles in the orthopaedic and radiology literature over the past 30 years using PubMed.

Results:

Ligament tears can be accurately assessed with MRI, but distinguishing partial tears from ruptures of the anterior cruciate ligament (ACL) can be challenging. Determining the extent of a partial tear is often extremely difficult to accurately assess. The status of the posterolateral corner structures, menisci, and cartilage can be accurately evaluated, although limitations in the evaluation of certain structures exist. Patellofemoral joint, marrow, tibiofibular joint, and synovial pathology can supplement physical examination findings and provide definitive diagnosis.

Conclusions:

MRI provides an accurate noninvasive assessment of knee pathology.

Magnetic resonance imaging and arthroscopic appearance of the menisci of the knee

The menisci are critical for normal function of the knee, providing shock absorption and load transmission that reduce stress on the articular cartilage. When torn, a meniscus may require surgery to restore function, reduce pain, and eliminate mechanical symptoms. Patterns of meniscal tears include longitudinal and bucket-handle, which are often reparable; and horizontal, radial, vertical flap, horizontal flap, and complex. Root tears are usually radial and occur in the posterior roots. When reviewing magnetic resonance images, one must be aware of normal variants and imaging pitfalls that may simulate pathology.

Meniscal injuries and imaging the postoperative meniscus

Meniscal injuries are common. Magnetic resonance imaging is considered the imaging modality of choice in diagnosing meniscal pathologic conditions in the nonoperative knee. Meniscal-preserving surgery is becoming more frequent, with a resultant increase in postoperative meniscal imaging, which is particularly challenging for the reporting radiologist. This article provides a review of the anatomy, pathologic conditions, and diagnostic pitfalls of meniscal injury, with a synopsis of the issues faced with postoperative meniscal imaging.

Unilateral meniscomeniscal ligament

Four normal variants of meniscomeniscal ligaments have been previously reported in the anatomy, arthroscopy, and radiology literature. The anterior and posterior transverse meniscal ligaments are the 2 most commonly observed, with a reported frequency of 58% and 1% to 4%, respectively. The last 2 variants include the medial and lateral oblique meniscomeniscal ligaments and account for a combined frequency of 1% to 4%.This article describes 2 patients with unilateral meniscomeniscal ligaments observed on magnetic resonance imaging. One patient had a unilateral lateral meniscomeniscal ligament extending from the anterior horn of the lateral meniscus to the posterior horn of the lateral meniscus and underwent conservative management. The second patient had a unilateral medial meniscomeniscal ligament with a concomitant medial meniscus tear and underwent arthroscopic intervention. The ligament was stable intraoperatively and, therefore, was not resected. Both patients had resolution of their symptoms.These 2 variants are additions to the previously described 4 normal intermeniscal ligament variants. The functions of the 2 new variants described in this article are poorly understood but are thought to involve meniscal stability. Accurate descriptions of normal variants can lead to the proper management of anomalous rare structures and prevent false imaging interpretations because these structures can closely mimic a double posterior cruciate ligament sign. Furthermore, an understanding of the various normal variants of intermeniscal ligaments can prevent unnecessary surgery that could result in further iatrogenic meniscus injury.

How I diagnose meniscal tears on knee MRI

OBJECTIVE

The goal of this article is to summarize the literature about the diagnosis of meniscal tears on MRI including the normal appearance of the meniscus and the appearance of the various types of meniscal tears. In addition, I discuss my experience with the causes of errors in the MR diagnosis of meniscal abnormalities and the nuances of meniscal abnormalities that can mimic a meniscal tear.

CONCLUSION

MRI is a highly accurate imaging method for diagnosing meniscal tears. To avoid errors in diagnosing meniscal tears, those interpreting MR examinations of the knee need to be aware of the attachments of the menisci and the normal variations in meniscal anatomy that may resemble a meniscal tear. In addition, by being aware of the patterns of meniscal tears, it is easier to diagnose the less common tears.

Normal MR imaging anatomy of the knee

Magnetic resonance (MR) imaging is the preferred imaging modality for evaluating internal derangement of the knee, due to its superior soft tissue contrast resolution, multiplanar imaging capability, and lack of ionizing radiation. The superb image quality facilitates learning of normal imaging anatomy and conceptualizing spatial relationships of anatomic structures, leading to improved understanding of pathologic processes, mechanisms of injury, and injury patterns, and ultimately increased diagnostic accuracy. This article depicts normal MR imaging anatomy and commonly encountered anatomic variants using representative MR images of the knee, and describes and explains the rationale of routine knee MR imaging protocol.

Ressonância magnética na avaliação das variações anatômicas meniscais e da anatomia ligamentar perimeniscal: potenciais causas de erro de interpretação

O conhecimento adequado das variações anatômicas meniscais e das estruturas perimeniscais é essencial para uma avaliação adequada dos exames de ressonância magnética do joelho, tanto no diagnóstico das lesões meniscais quanto para se evitar uma série de possíveis erros diagnósticos. Este artigo revê variações anatômicas que alteram o tamanho, a forma e a estabilidade meniscais e que incluem os vários tipos de menisco discoide, outras variações morfológicas meniscais menos frequentes e o ossículo meniscal. Também é revisada a anatomia de estruturas perimeniscais, principalmente ligamentares, que incluem os ligamentos meniscocapsulares, intermeniscais, meniscofemorais e extensões meniscoligamentares.

Magnetic resonance imaging of anatomical variations in the knee. Part 1: ligamentous and musculotendinous

Magnetic resonance imaging (MRI) is now the modality of choice for the investigation of internal derangement of the knee. Technological advances, including the wider availability of stronger magnets and new sequences, allows improved visualisation of smaller structures. Normal variants must be recognised as such, so that both over-investigation and mis-diagnosis are avoided. This article reviews both the well-recognised and the less common ligamentous and musculotendinous anatomical variants within the knee and illustrates their imaging characteristics on MRI.

MR imaging of meniscal and cartilage injuries of the knee

This article addresses the role of MR imaging in the evaluation of meniscal injuries, with emphasis placed on the common meniscal injuries, including horizontal, longitudinal, radial, and flap tears. An understanding of typical meniscal postoperative findings, together with those factors responsible for the misinterpretation of meniscal abnormalities, is essential for the accurate assessment of MR imaging in the athlete. This article also reviews the common articular cartilage injuries identified in the knee. MR imaging is the imaging modality of choice for the assessment of the menisci and articular cartilage, with the ready availability of MR imaging allowing for the rapid assessment of the injured athlete.

Potential pitfalls of a double PCL sign

The double posterior cruciate ligament (PCL) sign is seen on a midline sagittal MR image of the knee as a low-signal-intensity linear band paralleling the antero-inferior part of the PCL. Although the sign has a high specificity for a displaced bucket-handle tear of the medial meniscus, it can be mimicked by several normal and abnormal structures in the intercondylar region. Familiarity with these variants and identifying the other features supportive of meniscal injury will help to make a confident diagnosis of bucket-handle tear of the medial meniscus.

MR imaging of the meniscus: review, current trends, and clinical implications

MR imaging is the preferred imaging modality for evaluating the meniscus. Overall, when strict criteria are followed, it is accurate in diagnosing meniscal tears in patients who have not had prior meniscal surgery. However, an accurate interpretation requires a through knowledge of the normal meniscal anatomy, common meniscal variants, and common diagnostic pitfalls. In this article, the author emphasizes the importance of describing meniscal tears properly and discusses treatment options. Diagnosing a recurrent tear is more complicated in patients who have had prior partial meniscal resection or repair, and the use of MR arthrography in this group of patients is discussed. Recent developments in areas such as 3 T and parallel imaging offer promise for accurate meniscal evaluation with even shorter scan times.

MR Imaging of the Meniscus: Review, Current Trends, and Clinical Implications

MR imaging is the preferred imaging modality for evaluating the meniscus. Overall, when strict criteria are followed, it is accurate in diagnosing meniscal tears in patients who have not had prior meniscal surgery. However, an accurate interpretation requires a through knowledge of the normal meniscal anatomy, common meniscal variants, and common diagnostic pitfalls. In this article, the author emphasizes the importance of describing meniscal tears properly and discusses treatment options. Diagnosing a recurrent tear is more complicated in patients who have had prior partial meniscal resection or repair, and the use of MR arthrography in this group of patients is discussed. Recent developments in areas such as 3 T and parallel imaging offer promise for accurate meniscal evaluation with even shorter scan times.

MR imaging of the meniscus

It should be the goal of any radiologist who interprets MRI examinations of the knee to be able not only to recognize normal meniscal anatomy and accurately diagnose meniscal pathology, but also to develop a better grasp of the surgical implications of the imaging findings. By thinking more like an arthroscopist, one can provide a more clinically relevant report, and by doing so, add value to the work-up of a patient who presents with a potential meniscal tear.

Imaging of sports-related knee injuries

This article reviewed the major sports medicine conditions affecting the knee and their MR imaging appearance. MR imaging of the knee is considered efficacious especially in the setting of indeterminate clinical findings and can stratify patients, guiding further surgical management. MR imaging affects the diagnosis and management of acute knee injury by improving clinician diagnostic certainty, assisting in management decisions, and decreasing the number of arthroscopic procedures. From a societal perspective, knee MR imaging can be considered a cost-effective modality when compared with diagnostic and borderline therapeutic arthroscopies (e.g., debridement alone). For these and other reasons, knee MR imaging has shown a substantially increased use for the evaluation of sports medicine conditions.

Percutaneous tumor ablation: increased coagulation by combining radio-frequency ablation and ethanol instillation in a rat breast tumor model

PURPOSE

To determine if percutaneously applied radio frequency (RF) combined with percutaneous ethanol instillation (PEI) can increase the extent of ablation in rat breast tumors.

MATERIALS AND METHODS

R3230 mammary adenocarcinoma was implanted bilaterally in the mammary fat pads of 18 female rats. The tumor nodules measured 1. 2-1.5 cm. Eight tumors each were treated with (a) conventional, monopolar RF (96 mA +/- 28; 70 degrees C for 5 minutes); (b) PEI (250 microL of ethanol infused over 1 minute); (c) combined therapy of PEI immediately followed by RF ablation; or (d) combined therapy of RF ablation immediately followed by PEI. Four tumors were not treated and served as controls. Histopathologic examination included staining for mitochondrial enzyme activity. Resultant coagulation necrosis was compared between treatment groups.

RESULTS

Coagulation necrosis was observed only within treated tumors. Tumors treated with RF alone had 6.7 mm +/- 0.6 of coagulation surrounding the electrode, and those treated with PEI alone had 6.4 mm +/- 0.6 of coagulation around the instillation needle (not significant). Significantly increased coagulation of 10.1 mm +/- 0.9 (P: <.001) was observed with the combined therapy of PEI followed by RF. RF followed by PEI did not increase coagulation (6.4 mm +/- 0.8 around the needle; not significant).

CONCLUSION

PEI followed by RF ablation therapy increases the extent of induced coagulation necrosis in rat breast tumors, as compared with either therapy alone.