Chronic renal failure and endometrial osseous metaplasia: a hypothetical pathway

Sir, We would like to bring to general attention the case of a 44-year-old woman who came to our clinic because of spotting and occasional periods of amenorrhea. She had had menarche at the age of 14 years, followed by regular menstrual cycles. Her medical history revealed that she had one living child, and had subsequently experienced two miscarriages. The patient was human immunodeficiency virus (HIV) and hepatitis C virus positive. In addition, she was suffering from HIV-related chronic renal failure, HIV-related neuropathy and hepatitis C virus-related chronic hepatopathy. Physical and pelvic examinations were unremarkable. Transvaginal ultrasound examination revealed a hyperechogenic area in the uterine cavity measuring 14 mm × 6 mm. The patient underwent a diagnostic hysteroscopy, which showed a 20 mm × 10 mm white meshwork of bony spicules arising from the posterior wall, with a hard tactile consistency (Figure 1). A resectoscopic excision was then performed. The histological examination showed trabeculae of woven bone, and was consistent with osseous metaplasia of the endometrium. Concomitant endometrial histology showed a secretory endometrium. Two weeks after surgery, the patient again underwent a second transvaginal ultrasound examination, which revealed no trace of the original, abnormal ultrasound finding. Hysteroscopic aspect of osseous metaplasia of the endometrium. Osseus metaplasia is rarely encountered, with less than 100 cases reported in the international literature (1). There is controversy regarding the pathogenic mechanisms related to the histogenesis of heterotopic bone in the endometrium. A number of theories have been proposed, as follows: continuous and strong endometrial estrogenic stimulation; osteogenesis in the surrounding endometrium, which is promoted by retained fetal bones; implantation of embryonic parts without pre-existing bone after early-stage abortions; dystrophic calcification of retained and necrotic tissues, usually after an abortion; chronic endometrial inflammation, such as endometritis or pyometra; and metastatic calcification and metabolic disorders, such as hypercalcemia, hypervitaminosis D or hyperphosphatemia (1-3). The most recent and accepted theory is metaplasia of the endometrial stromal cells, usually fibroblasts, which change into osteoblasts and thus produce bone in the endometrium. A previous history of abortion is present in most of the reported cases, with osseous changes in the endometrium. Usually, the reproductive age group (between 20 and 40 years of age) is involved, although it has also been reported in the menopausal years (1). In the few reported cases in the literature, the time between the antecedent abortion and discovery of the endometrial ossification varies from eight weeks to 23 years (4). Chronic renal failure is a known cause of abnormal calcium–phosphorous metabolism with metastatic calcifications; this may be the pathway of osseous metaplasia observed in our patient. Ultrasound examination plays a primary role in the diagnosis of patients with osseous metaplasia. The characteristic hyperechogenic pattern is strongly suggestive of osseous tissue within the uterus and should be confirmed by hysteroscopic examination (2). Today, hysteroscopy is accepted as the gold standard for diagnosis and treatment. Bone formation in the endometrium is rare, but can be seen in malignant mixed Müllerian tumors and in teratomas, which should be considered in the differential diagnosis (1). Clinicians and pathologists should bear this chance in mind, particularly in light of the fact that an erroneous diagnosis may well result in unnecessary hysterectomy.