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Imaging findings of Hoffa’s fat pad herniation

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Abstract

Background

We report the radiologic findings of herniation of Hoffa’s fat pad through a defect in the lateral patellar retinaculum in young children who presented with painless masses visible by ultrasound (US) only with flexion of the knee.

Material and methods

Six children, between the ages of 1–8 years, presented with an anterolateral knee mass that was not tender and was only seen and palpable with knee flexion. An US was performed in all patients, magnetic resonance imaging (MRI) in 2 patients and knee radiographs in 1 patient.

Results

US imaging displayed focal herniation of Hoffa’s fat pad within the infrapatellar region through a defect of the lateral retinaculum, visible only during dynamic imaging when the knee was in flexion. MRI performed in knee extension did not demonstrate a mass; however, it revealed a focal defect in the lateral retinaculum in the region of the abnormality. Radiographs were normal.

Conclusion

Focal herniation of Hoffa’s fat pad is an uncommon cause of an anterolateral knee mass in young children. When a knee mass is only identified in flexion, focal fat herniation through a defect in the retinaculum should be suspected and a dynamic US should be performed.

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Authors and Affiliations

  1. Department of Radiology, Perelman School of Medicine at the University of Pennsylvania, The Children’s Hospital of Philadelphia, 34th Street and Civic Center Boulevard, Philadelphia, PA, 19104-4399, USA

    Nancy A. Chauvin & Asef Khwaja

  2. Department of Medical Imaging, Nemours Children’s Hospital, Orlando, FL, USA

    Monica Epelman

  3. Department of Radiology, Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA

    Michael J. Callahan

Authors
  1. Nancy A. Chauvin
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  2. Asef Khwaja
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  3. Monica Epelman
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  4. Michael J. Callahan
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Correspondence to Nancy A. Chauvin.

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Chauvin, N.A., Khwaja, A., Epelman, M. et al. Imaging findings of Hoffa’s fat pad herniation. Pediatr Radiol 46, 508–512 (2016). https://doi.org/10.1007/s00247-015-3515-5

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  • DOI: https://doi.org/10.1007/s00247-015-3515-5

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