A leiomyoma of the iris documented by immunohistochemistry and electron microscopy.

Purpose: To report an iris leiomyoma documented in accordance with today's stricter diagnostic criteria. Methods: Light microscopy, immunohistochemistry and electron microscopy were performed on the 3 mm ball-like, greyish-white vascularized tumour of the iris, close to the sphincter pupillae. Results: Light microscopy of the extirpated neoplasm showed the characteristic appearance of a leiomyoma with densely packed spindle-shaped cells, with oval nuclei and granular cytoplasm. On electron microscopic examination the tumour exhibited the characteristic features of a smooth muscle neoplasm. The immunohistochemistry was consistent with a myogenic tumour because the tumour cells were positive for smooth muscle actin and desmin, but negative for S-100 and melanin. Conclusion: The case illustrated the necessity of performing ancillary procedures such as electron microscopy and immunohistochemistry to substantiate a correct, although rare diagnosis.