HILUS (OR LEYDIG) CELL HYPERPLASIA
Ovarian hilus cells are morphologically similar to Leydig cells of the testes and are found in fetal ovaries then disappear during childhood to reappear at puberty. They are found in the majority of postmenopausal women in various numbers and distributions and characteristically ensheathe or lie within nonmedullated nerve fibers. Hilus cells should be distinguished from adrenal cortical rests in the mesovarium and lutein cells (thecal or stromal). Mild hilus cell hyperplasia is not uncommon and may be associated with an androgenic effect.
The distinction between extensive hilus cell hyperplasia and a hilus cell tumor can be difficult, although a diameter of 1.0 cm is frequently used as the minimum cutoff for a tumor. Hilus or Leydig cell tumors are included in the WHO classification under the heading of "Steroid Tumors" and are generally associated with a benign course. Reinke crystals, which are best demonstrated by Masson's trichrome or iron hematoxylin but frequently difficult to find, are required for the diagnosis of "Hilus or Leydig cell tumor" in ovarian tumors with vacuolated or granular eosinophilic cytoplasm. These tumors are usually positive for inhibin and Mart-1, can also be positive for vimentin and less frequently keratin and actin on paraffin section immunohistochemistry.
Contributed by Suzanne Bakdash, MD, MPH and Gloria Carter, MD