Korean J Radiol.  2016 Feb;17(1):159-165. 10.3348/kjr.2016.17.1.159.

T2 Relaxation Time Mapping of the Cartilage Cap of Osteochondromas

• Kim HK
• Horn P
• Dardzinski BJ
• Kim DH
• Laor T

• KMID: 2351176
• DOI: http://doi.org/10.3348/kjr.2016.17.1.159

Abstract

OBJECTIVE
Our aim was to evaluate the cartilage cap of osteochondromas using T2 maps and to compare these values to those of normal patellar cartilage, from age and gender matched controls.
MATERIALS AND METHODS
This study was approved by the Institutional Review Board and request for informed consent was waived. Eleven children (ages 5-17 years) with osteochondromas underwent MR imaging, which included T2-weighted fat suppressed and T2 relaxation time mapping (echo time = 9-99/repetition time = 1500 msec) sequences. Lesion origins were femur (n = 5), tibia (n = 3), fibula (n = 2), and scapula (n = 1). Signal intensity of the cartilage cap, thickness, mean T2 relaxation times, and T2 spatial variation (mean T2 relaxation times as a function of distance) were evaluated. Findings were compared to those of patellar cartilage from a group of age and gender matched subjects.
RESULTS
The cartilage caps showed a fluid-like high T2 signal, with mean thickness of 4.8 mm. The mean value of mean T2 relaxation times of the osteochondromas was 264.0 +/- 80.4 msec (range, 151.0-366.0 msec). Mean T2 relaxation times were significantly longer than the values from patellar cartilage (39.0 msec) (p < 0.0001). These findings were observed with T2 spatial variation plots across the entire distance of the cartilage cap, with the most pronounced difference in the middle section of the cartilage.
CONCLUSION
Longer T2 relaxation times of the cartilage caps of osteochondromas should be considered as normal, and likely to reflect an increased water content, different microstructure and component.

Keyword

T2 relaxation time mapping; Osteochondroma; Cartilage cap

MeSH Terms

Adolescent
Bone Neoplasms/*pathology
Cartilage, Articular/*pathology
Child
Child, Preschool
Female
Femur
Humans
Magnetic Resonance Imaging/*methods
Male
Osteochondroma/*pathology
Patella/*pathology
Retrospective Studies
Tibia

Figure

• 

  Fig. 1 T2 relaxation time mapping from 12-year-old boy with osteochondroma of femur. Gray scale map (A) and color-coded map (B) of distal femur. (A) Region of interest of cartilage cap was manually outlined on gray scale map. Mean T2 value of cartilage cap was 201.0 ± 35.4 msec, value of patellar cartilage was 40.4 ± 4.4 msec.

• 

  Fig. 2 9-year-old girl with osteochondroma of right proximal tibia (A, B) and 9-year-old girl in control group (C, D). A. Axial T2-weighted image with fat suppression demonstrates hyperintense signal of cartilage cap (arrows), which is similar to signal intensity of joint effusion of knee in age and gender matched control (C). C. Axial fast spin echo T2-weighted image with fat suppression demonstrates other forms of hyaline cartilage: unossified epiphyseal cartilage with low signal intensity (arrowheads), and articular cartilage with intermediate signal intensity (arrows). Axial color coded T2 maps of osteochondroma (B) and patellar cartilage (D) demonstrate different range of T2 relaxation times. Mean T2 values of cartilage cap in osteochondroma (172.8 ± 23.1 msec) were significantly longer than values (38.2 ± 5.2 msec) of patellar cartilage in control group.

• 

  Fig. 3 T2 spatial variation of cartilage cap obtained from 11 subjects with osteochondromas, and from patellar cartilage of age and gender matched controls. T2 relaxation times were significantly longer in cartilage caps across entire distance of cartilage (p < 0.0001). Difference is most prominent in middle portion of cartilage (at normalized distance between 0.4 and 0.8) where 0 represents osteochondral junction in osteochondroma and subchondral bone in patella; 1 represents external surface in osteochondroma and articular surface in patellar cartilage.

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