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Feature Christmas 2013: Strange Nativities

We wish you a merry x-ray-mas: Christmas signs in radiology

BMJ 2013; 347 doi: (Published 17 December 2013) Cite this as: BMJ 2013;347:f7020
  1. Rebecca Jane Wiles, specialty trainee in radiology1,
  2. Archita Gulati, specialty trainee in radiology1,
  3. Reena Dwivedi, specialty trainee in radiology2,
  4. Shivaram Avula, consultant radiologist3,
  5. John Curtis, consultant radiologist2,
  6. Laurence Abernethy, consultant radiologist3
  1. 1Department of Radiology, Royal Liverpool and Broadgreen University Hospitals NHS Trust, Liverpool L78XP, UK
  2. 2Department of Radiology, Aintree University Hospitals NHS Foundation Trust, Liverpool, UK
  3. 3Department of Radiology, Alder Hey Children’s NHS Foundation Trust, Liverpool, UK
  1. Correspondence to: R J Wiles rebeccajanewiles{at}

Radiological signs act as memory aids for clinicians and radiologists when attempting to recognise and recall how a particular radiological appearance relates to a condition. These signs are often associated with well known objects and several are related to Christmas. This article describes some familiar and more unusual Christmas related radiological signs that might be useful for trainees revising for examinations, as well as practising clinicians and radiologists.

Snow related signs

Christmas in Britain is anecdotally associated with snow—for example, snowy scenes are found on many greetings cards. Despite this, snow rarely falls on Christmas Day or in December. On average, snow or sleet falls on five days in December, compared with six days in March. Snow was seen on the ground somewhere in Britain on Christmas Day in 23 of the years between 1959 and 2010 (51 years). Snowfall itself (without settling on the ground) is more common, occurring on 29 Christmas Days over the same period.1

Despite the lack of evidence, Christmas is still traditionally associated with snow and several radiological signs are related to this frozen form of precipitation.

Snowcap sign

A snowcap is a cap-like crown of snow on the top of a mountain.2 The snowcap sign (fig 1) refers to the appearance of diffuse homogeneous sclerosis of the head of the humerus or femur during the revascularisation stage of avascular necrosis.3

Fig 1 Snowcap sign. (A) Frontal radiograph of the left shoulder showing increased sclerosis of the superior aspect of the humeral head, with flattening of the head (arrow) in keeping with avascular necrosis of the humeral head. (B) This has been likened to the appearance of a snow capped mountain

Avascular necrosis is caused by interruption of the blood supply of the femoral or humeral head, which leads to cell death. The disease process is …

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