Transcript Land Mine Radiology 2LT Justin P. Dodge and James

Case of the Day – Thursday
MUSCULOSKELETAL
Andrew J. Ziegert, MD1, Kirkland W. Davis1, MD,
Stacy E. Smith, MD2
1University
of Wisconsin Medical School, Madison, Wisconsin
2University of Maryland Medical System, Baltimore, Maryland
History: 32 year old female with knee pain.
(b)
(a)
(c)
Question: In this patient with medial meniscus extrusion, but no
degenerative joint disease, what is the most likely diagnosis?
Findings:
Figure 1 demonstrates medial
meniscal extrusion. To evaluate for extrusion of the
medial meniscus, one measures from the corner of the
medial tibial plateau to the peripheral margin of the
medial meniscus body1 (See Figure 2A).
This
measurement is taken on a mid-coronal image, where one
should also be able to see the medial collateral ligament2.
Three mm. or more of extrusion can be considered
pathologic2. In this case, the medial meniscus is extruded
6mm.
Figure 2A: Mid-coronal image of the knee (same as Figure 1) demonstrates measurement of medial meniscal extrusion (MME). One draws a vertical line at the point
of the medial tibial plateau where the cortex turns from vertical to horizontal, ignoring osteophytes1. MME is the distance from this line to the peripheral edge of the
medial meniscus (white arrow), measuring 6 mm. in this case. Black arrows denote medial collateral ligament.
Diagnosis: Medial meniscal root tear
Discussion:
It has been known for some time that medial meniscal extrusion
(MME) is associated with degenerative joint disease of the knee3,4. However, the patient in this
case has no degenerative disease, as stated. More recently, it has come to light that MME can
occur secondary to medial meniscal pathology, especially meniscal root and radial tears1,2.
The root of the meniscus is the tibial attachment of the posterior horn. In both the
medial and lateral menisci, the fibrocartilage of the meniscus makes a turn near the root and
fans out slightly, sometimes causing increased signal on T1- and proton density-weighted
images. Due to the uncertain anatomy in this location and the possibility of magic angle
phenomena, most radiologists have been reluctant to diagnose tears of the meniscal roots on
MRI. Recently, investigators have shown that tears do occur in this location and that they
often have clear findings on MRI5. The authors of this Case of the Day find that these tears
are usually easiest to detect on coronal images, where there will be a fluid gap on T2-weighted
images or obvious truncation of the meniscus (see Fig. 2B and C). Findings on sagittal images
are less obvious, but can perform a confirmatory role (see Fig. 2D, E, and F). To cause
significant MME, simple radial tears probably must be sizable. Complex tears of the medial
meniscus can also lead to MME1,2.
In this patient, MME provides a clue to the underlying meniscal root tear. Her case
points out that one must be attuned to the possibility of medial meniscal extrusion on MRI.
When it occurs, one should be even more vigilant in searching for meniscal root tears and
radial tears.
B
C
Figures 2B,C: Posterior coronal T1- (B) and fat-suppressed
proton density-weighted (C) images demonstrate abrupt cutoff of
the posterior horn of the medial meniscus near its root (arrow),
indicative of a root tear.
D
E
F
Figures 2D,E,F: Sequential sagittal proton density weighted images show disappearance of the
normal posterior horn of the medial meniscus as it approaches its expected attachment at the root,
confirming the root tear. Arrow denotes site of expected meniscal tissue, absent because of the tear.
References
1.
2.
3.
4.
5.
Costa CR, Morrison WB, Carrino JA. Medical Meniscus Extrusion on Knee MRI: Is Extent Associated with Severity of Degeneration or Type of Tear? AJR 2004; 183:17-23.
Lerer DB, Umans HR, Hu MX, Jones MH. The Role of Meniscal Root Pathology and Radial Meniscal Tear in Medial Meniscal Extrusion. Skeletal Radiology 2004; 33:569-574.
Kenny C. Radial Displacement of the Medial Meniscus and Fairbank’s Signs. Clinical Orthopaedics and Related Research 1997; 339:167-173.
Miller TT, Staron RB, Feldman F, Cepel E. Meniscal Position on Routine MR Imaging of the Knee. Skeletal Radiology 1997; 26:424-427.
Umans HR, Lerer DB, Hu MX, Jones MH. MR Imaging Findings of the Meniscal Root: Normal and Pathologic. Society of Skeletal Radiology Annual Meeting; Tucson, AZ, March 8, 2004.