This 23-year-old male had a nodule on his buttock, submitted to rule out dermatofibroma. Calcinosis cutis comes in a variety of flavors, this case representing a form a dystrophic calcification. Dystrophic calcification is usually secondary to trauma, although this history was not elicited in our patient. The buttock is often subject to trauma. The histology in this case is typical. The presence of calcium is often unambiguous on hematoxylin and eosin sections, but if in doubt, a von Kossa stain can help.
At higher power, the desposits are deeply basophilic and crystalline, consistent with calcium pyrophosphate. The size of the material ranges from granular to large polyhedral chunks. There is artifactual cracking and retraction spaces. The surrounding dermis is fibrotic with only a minimal inflammatory reaction.