MSK Case 2: MRI appearance of Focal Fibro-Cartilaginous Dysplasia (FFCD)

Marat Bakman, MD, Christopher Bang, DO, Gwy Suk Seo, MD, and Johnny U .V Monu, MD

Imaging Sciences URMC 2008
Publication Date: 2009-06-04

History

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.

Findings

Plain radiographs show isolated medial concave bowing deformity of the left tibia [Fig.1]. A well-defined lucent defect is present at the medial aspect of the metadiaphysis of the proximal tibia.

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.

Diagnosis

MRI appearance of Focal Fibro-Cartilaginous Dysplasia (FFCD)

Discussion

FFCD was first described in 1985 by Bell et al [1]. 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 [1].

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].

Diagnosis in a large number of cases is based largely on the characteristic appearance of the lesion on radiographs as well as the absence of other physical abnormalities.

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 [2] 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.

References

  1. Bell SN, Campbell PE, Cole WG, Menelaus MB. Tibia vara caused by focal fibrocartilaginous dysplasia: three case reports. J Bone Joint Surg[Br] 1985; 67:780-784. [PMID: 4055881]
  2. Choi IH, Kim CJ, Cho TJ, Chung CY, Song KS, Hwang JK, Sohn YJ: Focal fibrocartilaginous dysplasia of long bones: report of eight additional cases and literature review. J Pediatr Orthop 20: 421-427, 2000. [PMID: 10912595]
  3. Bradish CF, Davies SJM, Malone M. Tibia vara due to focal fibrocartilaginous dysplasia: the natural history. J Bone Joint Surg [Br] 1988; 70: 106-108. [PMID: 3339040]
  4. Langenskiold A. Tibia vara: a critical review. Clin Orthop Relat Res 1989; 246:195-207. [PMID: 2670387]
  5. Santili C, Prado JCL, Simis SD, Akkari M, Waisberg G, Kessler C. Focal fibrocartilaginous dysplasia: a rare form of spontaneously corrected varus knee. Rev Bras Orthop – Vol. 40, No 4 – April, 2005, 215-222.
  6. Ducou le Pointe H, Mousselard H, Rudelli A, Montagne JP, Filipe G. Blount's disease: magnetic resonance imaging. Pediatr Radiol. 1995;25(1):12-4. [PMID: 7761151]

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