A RARE CASE REPORT: OSSEOUS METAPLASIA IN UTERINE LEIOMYOMA

Fibroids or uterine leiomyomas are benign smooth muscle tumors which represent the most frequent neoplasm of reproductive tract, occurring in as many as 70% of women over a lifetime [1]. These tumors develop out of the myometrium and their development is affected by both hormonal, genetic, and growth factor-mediated mechanisms. Though benign, secondary degenerative changes are common in leiomyomas, which are typically caused by insufficient blood supply and usually involve hyaline, cystic, myxoid, red degeneration and calcification [2]. Among them, the presence of the ossification or the presence of the osseous metaplasia is extremely uncommon; it has been recorded in the literature no more than fifty times all over the world [3,4].

Osseous metaplasia is the process of the development of bone tissue in a non-osseous structure. When it develops in the uterus, it may take place either in the endometrium or myometrium usually after chronic inflammation, ischemia, necrosis, or after an instrument had been placed in the uterus [5]. Chronic ischemia or degenerative calcification is believed to activate the stromal fibroblasts or smooth muscle cells to differentiate into osteoblast-like cells which deposit osteoid and ultimately develop into bone in the case of leiomyoma [6].

Clinically, patients with calcified or ossified fibroids are often asymptomatic, but may present with lower abdominal pain, heaviness, menstrual irregularities, or pressure symptoms depending on size and location [7]. Radiological imaging such as ultrasound or computed tomography may reveal hyperechoic or calcified areas, yet differentiation between dystrophic calcification and true osseous formation requires histopathological confirmation [8].

We report a rare case of osseous metaplasia arising in a uterine leiomyoma in a postmenopausal woman, highlighting the clinicopathological features, histopathological findings, and differential diagnoses. This case adds to the limited body of literature describing such rare degenerative transformations.

Patient Presentation

A 56-year-old postmenopausal woman, gravida 3, para 3, presented with complaints of lower abdominal pain and lower backache for three months. She had her last childbirth 22 years ago and had undergone sterilization. Her medical history was significant for systemic hypertension, controlled with telmisartan 40 mg once daily. There was no history of vaginal bleeding, discharge, or previous gynecological surgery.

Clinical Examination

General physical examination was unremarkable, and vital parameters were stable. Abdominal examination revealed a firm, non-tender, suprapubic mass corresponding to a 12-week-size uterus. Per speculum and bimanual examination confirmed an enlarged, firm uterus with restricted mobility.

Radiological Evaluation

Pelvic ultrasonography demonstrated a posterior intramural fibroid measuring approximately 5×5 cm with dense calcification and echogenic areas consistent with degenerative changes (Figure 1). The ovaries were normal.

Surgical Procedure

A total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed under spinal anesthesia. Intraoperatively, the uterus was enlarged, and a hard, calcified intramural fibroid was noted in the fundal region (Figure 2). The specimen was sent for histopathological examination.

Histopathological Processing

The specimen was fixed in 10% neutral buffered formalin. Serial sections were processed, embedded in paraffin, and stained with hematoxylin and eosin. Microscopic examination was carried out under low and high power magnification.

Ethical Considerations

Institutional ethical norms were followed. The patient’s details were anonymized.

Gross Findings

The uterus measured 10×7×5 cm. On sectioning, a well-circumscribed, firm, intramural mass measuring 5×5 cm was identified in the fundal region. The cut surface revealed grey-white whorled areas with focal gritty and bony-hard consistency (Figure 5). No areas of hemorrhage or necrosis were evident.

Microscopic Findings

Histopathological examination revealed interlacing bundles of smooth muscle cells consistent with leiomyoma. Within these, there were irregular trabeculae of mature lamellar bone formation lined by osteoblasts (Figures 3 and 4). The intervening stroma showed fibrosis with scattered calcific deposits. No atypia, mitotic activity, or necrosis suggestive of malignancy was noted.

Diagnosis

The histopathological diagnosis was leiomyoma with osseous metaplasia.

Postoperative Course

The patient’s postoperative period was uneventful. She was mobilized on the first postoperative day, tolerated oral intake, and was discharged on the third day with complete resolution of symptoms.

Tables

Table 1. Summary of patient’s clinical and radiological features

Table 2. Intraoperative and gross findings

Table 3. Histopathological summary

Figures

FIGURE 1: ULTRASOUND PELVIS SHOWING POSTERIOR INTRAMURAL FIBROID (FIGO TYPE 4) WITH CALCIFIC/OSSEOUS CHANGE.

FIGURE 2: GROSS INTRAOPERATIVE SPECIMEN SHOWING ENLARGED UTERUS WITH CALCIFIED INTRAMURAL FIBROID

.

FIGURE 3: PHOTOMICROGRAPH (H&E, ×10) SHOWING TRABECULAE OF BONE WITHIN LEIOMYOMATOUS TISSUE.

FIGURE 4: PHOTOMICROGRAPH (H&E, ×40) DEMONSTRATING MATURE LAMELLAR BONE LINED BY OSTEOBLASTS.

FIGURE 5: INTRAOPERATIVE SECTIONING OF FIBROID SHOWING HARD, WHITISH BONY AREA WITHIN SMOOTH MUSCLE TISSUE.

Osseous metaplasia in uterine leiomyoma is a rare phenomenon that reflects an advanced stage of degenerative change within a benign tumor. The first documented case was reported by Von Rokitansky in the 19th century, and only sporadic reports have been published since then [9].

The precise mechanism remains uncertain. Proposed theories include dystrophic calcification secondary to necrosis, chronic ischemia, or metabolic abnormalities in calcium metabolism [10]. Another hypothesis suggests that pluripotent mesenchymal cells or fibroblasts within the myometrium undergo metaplastic transformation into osteoblasts under persistent irritation or hypoxia [11]. In some cases, retained fetal bone following abortion or chronic endometrial inflammation has been implicated, though this mechanism primarily applies to endometrial ossification rather than myometrial lesions [12].

Most cases occur in perimenopausal or postmenopausal women presenting with nonspecific pelvic symptoms. The rarity and nonspecific imaging findings make preoperative diagnosis difficult. Ultrasound may reveal dense echogenic areas with posterior acoustic shadowing, often interpreted as calcification [13]. Computed tomography or MRI can demonstrate high-density areas corresponding to ossification, but histology remains the gold standard [14].

Microscopically, osseous metaplasia must be distinguished from heterologous elements of malignant mixed Müllerian tumors or leiomyosarcomas, which show cellular atypia, mitotic activity, and immature osteoid [15]. In benign metaplasia, bone trabeculae are mature, lined by osteoblasts, and lack atypia or mitosis.

A review of the literature reveals very few similar cases. Yadav et al. reported a case of osseous metaplasia in a fibroid in a 48-year-old woman with similar histopathological findings [16]. Jaiswal et al. described a comparable case in a 52-year-old postmenopausal woman, emphasizing chronic ischemia as the likely trigger [17]. Gadre et al. and Singh et al. have also documented isolated occurrences in postmenopausal women following degenerative transformation [18,19]. These consistent demographics highlight that hormonal withdrawal and vascular insufficiency play central roles in pathogenesis.

Surgical excision remains curative. No recurrence or malignant transformation has been documented. Recognition of osseous metaplasia is essential to prevent misdiagnosis as a malignant mixed tumor or metastatic calcification

Osseous metaplasia within a uterine leiomyoma is an exceedingly rare entity encountered predominantly in postmenopausal women. It likely represents an end-stage degenerative process following chronic ischemia or dystrophic calcification. Diagnosis is histopathological, as radiology alone cannot distinguish ossification from calcification. Awareness of this condition is crucial for pathologists and gynecologists to avoid diagnostic pitfalls. Total hysterectomy remains both diagnostic and therapeutic, with an excellent prognosis.

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