Frostbite is a focal tissue injury from exposure to extremely low temperatures, and most commonly involves the fingers and toes. It is most commonly encountered in radiology in a differential for acro-osteolysis.
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Clinical presentation
Most common on exposed areas: hands, feet, face and ears. The skin changes texture ("waxy") and may develop bullae if the frostbite is severe.
Pathology
Tissue injury from frostbite occurs in two ways 1:
direct tissue necrosis from freezing
indirect tissue injury from inflammatory changes and release of inflammatory mediators
Radiographic features
May be useful to help determine the degree of injury or presence of secondary injury in patients who present clinically with frostbite.
Plain radiograph
acro-osteolysis of the distal phalanx / phalangeal tuft
swelling of affected soft tissues
it has been reported that the thumb may be relatively spared (the patient is likely to wrap their thumb in their palm) 2
MRI
Limited data suggests that MRI may be a useful modality for demarcating ischemic tissue 4.
Nuclear medicine
Tc-99m-MDP (bone scintigraphy)
A two-phase scan may be useful to assess the viability of tissue 3. A combination of the perfusional phase and soft tissue phase can help characterize areas of inflammation and areas of ischemia (increased or decreased radiotracer activity, respectively).
Treatment and prognosis
Clinically, frostbite is classified similarly to burns: 1st-4th degree.
Incautious thawing of the tissue may lead to worsened injury (higher degree burn) from the ensuing inflammatory reaction.
Treatment of systemic hypothermia should be prioritized over frostbite.
Differential diagnosis
frostnip: focal tissue injury without permanent damage
immersion foot: frostbite and immersion in water (a type of trench foot)
Imaging differentials are that of acro-osteolysis.