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Meniscal ossicle mimicking a radial meniscal tear

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Case Presentation

A 12-year-old boy with a known history of juvenile idiopathic arthritis (JIA) presented with pain in the left knee with associated joint effusion after a fall during ice- skating. Coronal fat-saturated (FS) proton density mag- netic resonance imaging (MRI) revealed a hypointense structure at the intercondylar site of the posterior region of the medial meniscus (MM), which was initially inter- preted as a meniscal fragment adjacent to a radial tear of the MM (Figure 1). Arthroscopy, however, was negative

for a meniscal tear and demonstrated synovitis resulting from underlying JIA. MRI was repeated because of persis- tent symptoms and revealed a well-defined lesion within the fibrocartilage of the posterior horn of the MM. The center of the lesion was iso-intense to bone marrow with a peripheral hypointense rim on coronal T1-weighted images (WI) (Figure 2), indicative of a meniscal ossicle. In retrospect, this was not visible on sagittal T1-WI of the ini- tial MRI. Radiograph confirmed a well-defined triangular ossification in the posteromedial joint space (Figure 3).

JIA was conservatively treated.

Comment

A meniscal ossicle is rare with a prevalence around 0.15%

[1]. A meniscal ossicle consists of mature lamellar and can-

Vangrinsven G, Vanhoenacker F. Meniscal Ossicle Mimicking a Radial Meniscal Tear. Journal of the Belgian Society of Radiology. 2020;

104(1): 33, 1–3. DOI: https://doi.org/10.5334/jbsr.2125

* AZ Sint-Maarten, BE

University (Hospital) Antwerp/Ghent, BE Corresponding author: Filip Vanhoenacker (filip.vanhoenacker@telenet.be)

IMAGES IN CLINICAL RADIOLOGY

Meniscal Ossicle Mimicking a Radial Meniscal Tear

Guillaume Vangrinsven

*

and Filip Vanhoenacker

*,†

Teaching Point: A meniscal ossicle may be misdiagnosed as a tear of the posterior horn of the medial meniscus or an intra-articular loose body.

Keywords: meniscal ossicle; meniscal root; meniscal tear; MRI; radiography

Figure 1.

Figure 2.

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Vangrinsven and Vanhoenacker: Meniscal Ossicle Mimicking a Radial Meniscal Tear Art. 33, page 2 of 3

cellous bone surrounded by cortex and cartilage, embed- ded within the meniscus. The majority of ossicles are solitary and located in the posterior horn of the MM [1].

The etiology is still debated. Heterotopic ossification after single or repetitive trauma is often proposed as a patho- genetic mechanism. The presence of other intra-articular lesions in a large percentage of cases supports this theory, but conclusive arguments are still missing. Other theories include vestigial remnants, mucoïd degeneration, and tibial avulsion fracture of the meniscal root insertion [1].

Meniscal ossicle can be an incidental finding in asymp- tomatic patients, although most patients present with intermittent pain and joint effusion. Because of frequent coexisting intra-articular lesions, it is unclear whether these symptoms can be attributed to the meniscal ossicle.

Radiographs show a triangular or rectangular opac- ity usually at the posteromedial joint space, often mis- diagnosed as a loose body. On MRI, location within the posterior horn of the MM differentiates it from a loose body, avulsion fracture of the semimembranosus tendon, and chondrocalcinosis. Furthermore, the ossicle appears isointense to bone marrow and is circumscribed by a hypointense rim on all sequences. The increased signal

compared to the low signal of the fibrocartilage of the meniscus can mimic a tear. We highly recommend includ- ing T1-WI in at least one plane to the MRI protocol. This allows characterization of the fatty bone marrow content of the ossicle and to exclude chondrocalcinosis, which is of low signal on T1-WI. Because the causal relationship of the meniscal ossicle with the clinical presentation is not clear, the radiologist should scrutinize the knee for other abnormalities.

Conservative treatment of the meniscal ossicle is favoured. Arthroscopic resection may be considered in case of persistent symptoms and suspicion of posttrau- matic etiopathogenesis of the meniscal ossicle [1].

Competing Interests

The authors have no competing interests to declare.

Reference

1. Mohankumar R, Palisch A, Khan W, White LM, Morrison WB. Meniscal ossicle: Posttraumatic ori- gin and association with posterior meniscal root tears. AJR. 2014; 203: 1040–6. DOI: https://doi.

org/10.2214/AJR.13.11821 Figure 3.

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Vangrinsven and Vanhoenacker: Meniscal Ossicle Mimicking a Radial Meniscal Tear Art. 33, page 3 of 3

How to cite this article: Vangrinsven G, Vanhoenacker F. Meniscal Ossicle Mimicking a Radial Meniscal Tear. Journal of the Belgian Society of Radiology. 2020; 104(1): 33, 1–3. DOI: https://doi.org/10.5334/jbsr.2125

Submitted: 29 March 2020 Accepted: 29 May 2020 Published: 26 June 2020

Copyright: © 2020 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. See http://creativecommons.org/licenses/by/4.0/.

Journal of the Belgian Society of Radiology is a peer-reviewed open access journal OPEN ACCESS

published by Ubiquity Press.

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