Post-traumatic cystic bone lesion

Last revised by Dr Francis Fortin on 08 Feb 2021

Post-traumatic cystic bone lesions, also known as fracture cysts or transient fatty cortical defects, are benign, transient post-fracture cysts, which are relatively uncommon and usually appear about one-to-two months after traumatic fracture.

They are rare but may be under-recognized, as monitoring after fracture often is only clinical. They have most often been reported in children of growing age. The most common reported site is the distal radius 1-3.

Though mostly asymptomatic in nature, patients with these transient lesions can present with moderate soft swelling 1.

Characteristics of these lesions are:

  • non-expansile cyst of <1 cm in diameter
  • may be multiple
  • close proximity to former fracture site
  • may contain fat

Typically encountered at about a month after initial fracture, they have been reported to occur as late as 18 months after the initial trauma 1.

There is ongoing debate whether these transient lesions represent intramedullary fat inclusions cysts (most accepted theory) or resorption cysts of excessive periosteal reaction caused by subperiosteal hematoma or intraosseous hemorrhage 1,3.

Typical appearances are that of a subcentimeter oval or round lucency without expansivity, peripheral condensation or periosteal reaction and close proximity to the site of former fracture.

They can sometimes show well-defined intracortical fatty density 6,7.

May show fatty signal, with signal loss on fat suppressed sequences 1.

As all hitherto reported lesions resolved spontaneously, no treatment is needed.

Encountering a cyst-like lesion close to a healing fracture (probably even greenstick fracture) can make the diagnosis straightforward. More challenging diagnostic scenarios, however, can comprise lack of former studies (or unawareness of their existence, unavailability at other institutions, etc), incomplete clinical information or a long period between initial fracture and lesion on actual imaging studies.

In those cases and in general differential diagnostic considerations may include:

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