MSK Case 2: MRI appearance of Focal Fibro-Cartilaginous Dysplasia (FFCD)
Imaging Sciences URMC 2008
Publication Date: 2009-06-04
A 2-year-old girl was seen 9 months earlier with for bowing deformity of the legs. The mother reported initial bowing of both legs with weight-bearing. However while the right leg improved, the left leg appeared progressively worse.
She was born full-term with no birth defects. Developmental milestones were normal and the child walked at 11 months. Physical examination revealed a left genu varus deformity. Both upper and lower extremities showed normal muscle tone and strength. Radiographic studies performed at initial presentation were characteristic. The patient was fitted with knee orthotics and is currently being followed with some improvement seen.
MRI [Fig. 2] showed a focal linear signal alteration in the metadiaphysis of the proximal medial tibial with adjacent sclerotic margins. The signal pattern is mixed intermediate-to-low signal on all sequences. The linear low-signal similar to that of a tendon/ligament can be followed till it embeds within the medullary bone. The pes anserinus tendons were noted to insert separately and away from the area of lesion.
FFCD was first described in 1985 by Bell et al . Of the three earlier reported cases, two underwent osteotomies. Pathologic specimens showed well-delineated mass of dense fibrous tissue resembling tendon with fibroblasts seen within lacunae. Proximity of FFCD lesions to pes anserinus insertion was noted and it was suggested that the lesion may be the result of abnormal mesenchymal differentiation with persistence as focus of fibrocartilage .
Since then more cases of FFCD have been described in the tibia as well as in other locations including the femur, humerus and ulna [2-5]. In some of these, dense fibrous tissue associated with cartilage was seen on histology [3,5].
Plain radiographs typically show a sharply delineated, radiolucent cortical-based defect with sclerotic margins located in the meta-diaphysis of the bone in question. Thus the radiographic appearance of FFCD is often diagnostic. An excellent correlation can be made between the microscopic findings of FFCD and MRI. For this reason MRI may be obtained to support the diagnosis in atypical or in extra-tibial lesions.
In a great number of FFCD no surgical intervention was required and a natural correction occurred until four years of age [2,3]. However Choi et al  pointed out that femoral and humeral FFCD do not have the potential for spontaneous regression of the deformity and such cases may need surgical correction.
Other causes of tibia vara, may be considered in the differential diagnosis, especially Blount’s disease. Blount’s disease in its infantile form more commonly involves both extremities, has well-described metaphyseal deformity and lacks a well-defined defect in proximal metadiaphysis [4,6].
Conclusion: Focal fibrocartilaginous dysplasia is an uncommon lesion seen in children under 2 years of age. It is a benign self-limiting entitiy. The associated deformity often corrects itself without surgery in 1 to 6 years. The characteristic radiologic findings of this lesion differentiate it from other similar conditions. MRI should be used to confirm the diagnosis in atypical presentations.
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