Posthysterectomy pelvic leiomyomas with pseudo-Meigs syndrome and metastasis to gluteal soft tissue

Introduction

Benign metastasising leiomyoma (BML) is a rare condition marked by well-differentiated smooth muscle tumours appearing outside the uterus in women with a history of uterine leiomyoma. Metastasis from leiomyoma is found to be most common in the lungs (79.5%), but other organs, including the heart, lymph nodes, spine and soft tissues, can also be affected.1 2 Fitzhugh et al reported that deep soft tissue metastasis of benign leiomyoma is very rare, with only 60 cases documented in the English literature up to that point.3 We describe a similar case of posthysterectomy pelvic leiomyoma with gluteal soft tissue metastasis.

Case presentation

A woman in her 50s, gravida two para two, presented to our institution with complaints of abdominal distension and pain. The patient has a history of myomectomy done for uterine fibroid in her 20s, followed by a hysterectomy for recurrent fibroid at the age of 38 years. MRI of the abdomen revealed left-sided mild pleural effusion, moderate ascites with a heterogeneously enhancing mass of size 18.0×11.0×11.0 cm in pelvis causing mass effect on bilateral ureters with mild to moderate bilateral hydroureteronephrosis (left>right) and an enhancing lesion of size 6.1×5.0 cm in right gluteus muscle (Figure 1).

Multiple biopsies of the tumours taken revealed a spindle cell neoplasm with stromal hyalinsation. An immunohistochemistry (IHC) was done for the pelvic mass, which showed features favouring leiomyoma with degeneration. A multidisciplinary tumour board was held, which decided on surgery in two sittings. Primary surgery was to be done for the mass in the pelvis, followed by resection of the gluteal mass.

She underwent midline laparotomy. There was moderate ascites present and a solid pelvic mass with cysts in the upper part; a capsule breach was found, probably due to a prior trucut biopsy. There were adhesions to the left pelvic wall, urinary bladder, denser adhesions to the rectal and sigmoid colon mesentery along with omental adhesions to the anterior abdominal wall. We proceeded with bilateral adnexectomy with pelvic tumour excision and infracolic omentectomy (figure 2).

The postoperative period was uneventful and the patient was discharged on the sixth day with advice for follow-up.

The patient was posted for the second surgery after a few weeks of recovery from abdominal surgery. Contrast-enhanced CT of the abdomen with pelvis showed a well-defined mass lesion of size 6.1×5 cm in the right gluteus muscle. A lazy S-shaped incision was placed on the right gluteal region, which included the previous biopsy scar. A wide local excision of the tumour was done. The patient is asymptomatic on follow-up after 1 year post procedure.

Histopathological examination of the abdominal mass reveals a well-defined, encapsulated neoplasm composed of spindle cells arranged in sheets and interlacing bundles. The cells exhibit moderate eosinophilic cytoplasm and cigar-shaped vesicular nuclei, with minimal mitotic activity. No necrosis is observed, but areas of cystic degeneration are present. In the gluteal mass, the lesion is characterised by a neoplasm with cells arranged in cords, trabeculae, diffuse patterns and sheets (figure 3). IHC of both the neoplasms was done; alpha, smooth muscle was positive for both the samples, while S100 (for neural sheath malignancy), CD10 (endometrial stromal tumour), CD117 (GIST, Gastro Intestinal Stromal Tumors), CK (epithelial tumours), CD34 (sarcoma) was negative, while Ki67 was 5% (figure 4). Adnexal tissue was normal. Findings were discussed in the multidisciplinary tumour board and a diagnosis of post-hysterectomy leiomyoma pelvis with pseudo-Meigs syndrome and soft tissue metastasis was confirmed.

Discussion

Leiomyomas, driven by hormonal factors, can also originate in the vulva, ovaries, bladder and urethra.4 5 Additionally, they have been rarely found in the tissues of the bone, deep soft tissues, skin, mediastinum, skeletal and cardiac muscles, lymph nodes, omentum, mesentery and retroperitoneum.6 A few atypical presentations of leiomyomas documented in the literature are BML, intravenous leiomyomatosis, disseminated peritoneal leiomyomatosis, retroperitoneal leiomyomatosis and parasitic leiomyoma.4 5 BML is a rare condition that occurs in women with a history of uterine leiomyoma, where the tumours metastasise to locations outside the uterus.2 4 5 The pathogenesis of BML remains uncertain. However, it is hypothesised that BML may spread via the bloodstream, arise from multiple independent foci and/or be influenced by hormonal factors.4 5

The mechanism of BML has been explored in multiple studies and remains a subject of debate. It is most frequently observed after uterine myomectomy or hysterectomy. One suggested theory is that surgical intervention may promote haematogenous spread of the tumour to different sites. Given the patient’s history of myomectomy and hysterectomy, the possibility of haematogenous dissemination cannot be ruled out. There are also some cases where BML has occurred without prior history of surgery.7–9 For a woman of this age, the differential diagnosis encompassed a variety of conditions, such as an ovarian tumour, endometrioma and soft tissue sarcoma. Steiner in 1939 was the first to report BML and there have been a variety of cases reported since then.10

Though rare, leiomyomata of the deep soft tissue have been described previously in case reports.3 11–15 Metastasis of uterine fibroids most commonly appears several years after the diagnosis and removal of uterine leiomyomas by hysterectomy. Consequently, prior gynaecological surgeries, such as hysterectomy or myomectomy, are risk factors for developing these rare growth patterns originating from benign uterine fibroids.5 Data from Steiner et al are consistent with previous case reviews, which describe the interval between hysterectomy and BML diagnosis as ranging from 3 years to 20 years, with an average of 10 years.10 The patient described in this report presented with BML after 16 years post hysterectomy. Meigs’ syndrome is characterised by a triad of ovarian fibroma, pleural effusion and ascites. In contrast, pseudo-Meigs’ syndrome is a rare condition involving a benign or malignant pelvic or abdominal tumour, excluding ovarian fibroma or fibroma-like tumours, accompanied by hydrothorax and ascites, which resolve following tumour resection.16 17 Since the patient presented with a benign pelvic tumour associated with ascites and pleural effusion, which resolved following the resection, it was found to be a case of pseudo-Meigs syndrome.

Billings et al histologically divide such leiomyomas into two distinct subtypes: leiomyomas of somatic soft tissue and retroperitoneal-abdominal leiomyomas. The latter likely originates from hormonally sensitive smooth muscle. Although they resemble uterine leiomyomas, they are found at locations distant from the uterus and are likely independent soft tissue primaries rather than parasitic leiomyomas of the uterus.11 The soft tissue nodules are composed of spindle-shaped smooth muscle cells, sometimes containing fibroblasts and myofibroblasts, without atypia or mitosis (<1/50 per high power field). The morphological arrangement is similar to that of typical uterine leiomyomas.18

IHC was crucial for us to compare both tumours and determine their relationship, as the gluteal and pelvic lesions shared similar histopathology. Following a multidisciplinary tumour board discussion, it was concluded that the lesions were of the same clonal origin, suggesting a rare metastatic event, and the patient was advised close follow-up with consideration of hormonal therapy if recurrence occurs. Although DNA studies were discussed, further evaluation was deferred due to the benign nature of the disease and resource constraints.

Conclusion and clinical implications

BML is a rare but significant entity that should be considered in women with a history of uterine leiomyomas, particularly those who have undergone myomectomy or hysterectomy. This case highlights the importance of recognising atypical presentations of BML, such as deep soft tissue metastasis, which can mimic malignant neoplasms. The presence of pseudo-Meigs’ syndrome further complicates the diagnosis, emphasising the need for thorough clinical, radiological and histopathological correlation. IHC plays a crucial role in differentiating BML from other soft tissue neoplasms and guiding appropriate management strategies. Surgical excision remains the mainstay of treatment, with generally favourable outcomes, as seen in this case. Long-term follow-up is essential, as BML can present years after the initial uterine surgery.