Jean-Luc Drapé, Sophie Goettmann, Alain Chevrot and Jacques Bittoun
Ultrasonography Magnetic resonance imaging Conclusion Further reading
It may seem surprising to devote an entire chapter to imaging of the perionychium, as traditionally this structure has been difficult to investigate radiologically. However, high-frequency transducers now allow accurate ultrasonographic imaging of the finger tips. Magnetic resonance imaging (MRI) of the nail unit is also available, thanks to small dedicated surface coils. These new resources could modify the imaging strategy of ungual and subungual diseases.
The main indication for these new techniques is the investigation of nail tumours. Tumours of the perionychium may be difficult to diagnose because of this structure's anatomic peculiarities. Symptoms, growth, and above all the appearance of the tumours may be modified by the screen produced by the nail plate. Deep tumours that originate close to the nail root are covered by the posterior nail fold and may only be expressed by nail dystrophy. Thus, every suspect lesion of the nail unit should be investigated by radiography and biopsy. Complementary imaging should help in difficult cases by confirming and accurately locating the periungual mass.
Radiographs remain the essential means of imaging the nail unit. They are essential for study of the distal phalanx, but show very little of the soft tissues. The technique is adapted by use of high-resolution one-layer breast films or dedicated digital films. Posteroanterior and lateral views of the involved finger usually are sufficient. Oblique views may be necessary to highlight subtle erosions of the phalanx. Most nail dystrophies should benefit from radiography before surgical investigation. These radiographs can show abnormalities of the soft tissues, such as a thickening of the posterior nail fold with a mucoid cyst. Comparative lateral radiographs can highlight a difference in thickness of the nail bed when a subungual mass is present. Radiographs may depict soft-tissue calcifications as phleboliths of a haemangioma. Bone tumours may be suspected with pedicled ossifications of an exostosis, or mottled calcifications of a paraosteal chondroma. Enchondroma may expand the distal phalanx and be complicated by a pathologic fracture. Dense bone abnormalities may be secondary to an osteoid osteoma or to psoriatic arthropathy with periosteitis. When a mucoid cyst is suspected, a lateral view is suitable to highlight osteoarthritis of the distal interphalangeal phalanx with dorsal osteophytes impinging on the distal band of the extensor tendon. Erosion of the distal phalanx may be depicted in several diseases, as invasive subungual squamous carcinoma or keratoacanthomas, glomus tumours or epidermoid cysts.
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