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Plantar Fat Pad Signal Changes Are Commonly the Result of Fibrosis and Adventitial Bursitis

April 9, 2008
Written by: , Filed in: Musculoskeletal Radiology
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The objective of a recent study was to detect PFP signal changes on MR imaging on asymptomatic volunteers, and to correlate with histopathologic findings in cadavers and patients.

The study has concluded that plantar fat pad (PFP) signal changes are commonly seen under the first and fifth metatarsal heads in asymptomatic feet. Histology demonstrates fibrosis and adventitial bursitis.

Participants
70 asymptomatic volunteers (aged 21 to 69 years, M=F) were imaged in this retrospective analysis.

Methodology
Plantar signal alterations were defined as ovoid or round signal intensity changes underneath the metatarsal heads in at least two adjacent images. Signal intensity was compared to skeletal muscle on T1 and T2. The greatest dimension was measured in the coronal plane.

Six cadaver forefeet were examined and after imaging, the forefoot PFP including the skin was excised and sectioned in the coronal plane corresponding to the MR imaging plane. Six patients with history of forefoot pain and subsequent excision or ultrasound-guided biopsy of the PFP were included and their imaging studies reviewed.

MDCT and MR Update: Body and Musculoskeletal Imaging

University of California San Francisco, Department of Radiology and Biomedical Imaging
MDCT and MR Update: Body and Musculoskeletal Imaging program features helical multi-detector row CT (MDCT) and MRI as it applies to diseases in the chest, abdomen and pelvis, and musculoskeletal system. Newer and established cross-sectional methods are discussed. Click here to read more or order:

MDCT and MR Update: Body and Musculoskeletal Imaging

Results of the Study
59 (84%) of asymptomatic forefeet showed a total of 103 PFP signal changes, mostly beneath the first (70%) and fifth (61%) metatarsal heads. All signal changes were isointense to skeletal muscle on T1, 91% were hypointense compared to skeletal muscle on T2, 8% were isointense, and 1% was hyperintense.

Overall, 87% demonstrated blurred margins and 88% extended from the skin to the flexor tendon. Lesion size median and 90th percentile ranged from 10 to 12 mm and 13 to 16 mm, respectively. There was a slight female predominance (60% versus 40%).

Four of the cadaver feet showed a total of 11 signal alterations in a similar distribution pattern. All changes were isointense on T1 and hypointense on T2, with blurred margins in 8 of 11 lesions. Histologically, various amounts of fibrosis were demonstrated. Nine fat pad alterations demonstrated a cavity resembling a bursa within the area of fibrosis. The six patients had a total of six fad pad changes.

The two largest changes were predominately hyperintense on T2. Lesion size median and 90th percentile were 20 and 27 mm, respectively. In two patients, histology demonstrated fibrous capsules surrounding cavities with fibrin-lined papillary projections. One patient had a partially calcified chondroma and three patients had fibrosis and mild inflammation.

Conclusions
PFP signal changes are commonly seen under the first and fifth metatarsal heads in asymptomatic feet. Histology demonstrates fibrosis and adventitial bursitis.

Reviewer’s Comments
“Pressure lesions” are frequently observed in foot and ankle imaging, supporting the “tripod model” of weight bearing, although they could also be related to footwear. Pressure lesions may not be responsible for the patients’ foot pain.

Author: Cornelia Wenokor, MD

Reference
Studler U, Mengiardi B, et al. Fibrosis and Adventitious Bursae in Plantar Fat Pad of Forefoot: MR Imaging Findings in Asymptomatic Volunteers and MR Imaging-Histologic Comparison.
Radiology; 2008; 246 (March): 863-870:

MDCT and MR Update: Body and Musculoskeletal Imaging

University of California San Francisco, Department of Radiology and Biomedical Imaging
MDCT and MR Update: Body and Musculoskeletal Imaging program features helical multi-detector row CT (MDCT) and MRI as it applies to diseases in the chest, abdomen and pelvis, and musculoskeletal system. Newer and established cross-sectional methods are discussed. Click here to read more or order:

MDCT and MR Update: Body and Musculoskeletal Imaging

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