Post-traumatic cystic bone lesion

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

Epidemiology

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

Pathology

Characteristics of these lesions are:

• non-expansile cyst of less than 1 cm in diameter,
• may be multiple
• close proximity to former fracture site.

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.

Aetiology

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.

Clinical presentation

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

Radiographic appearance

Plain films

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

Treatment

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

Differential Diagnosis

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:

• unicameral bone cyst - usually expansile
• non-ossifying fibroma (fibroxanthoma) - larger
• transient cyst-like cortical lesions
• osteomyelitis - usually symptomatic, abnormal blood samples