Recurrent leiomyoma of the vulva mimicking peripheral nerve sheath tumour

Abstract

Leiomyoma, a benign monoclonal tumour, is very rarely found in extrauterine sites, especially in the vulval region. Histopathology of the soft tissue tumours affecting this region is similar and immunohistochemistry (IHC) may be essential to confirm the diagnosis. We report a case of a 63-year-old postmenopausal woman who presented with a recurrent vulval mass involving the clitoris and left labia majora with suspected urethral involvement. Although the wedge biopsy was reported as peripheral nerve sheath tumour, staining with smooth muscle actin clinched the diagnosis of leiomyoma, highlighting the importance of IHC for diagnosis.

Background

Leiomyoma, a benign monoclonal smooth muscle tumour, commonly arises from uterine myometrium. Extrauterine leiomyoma, being extremely rare, can arise from the vulva, vagina, ovaries, urinary bladder, urethra, round ligament, sinonasal cavities and kidney.¹ Here, we report a case of recurrent vulval leiomyoma, involving the clitoris and left labia majora with suspected urethral involvement, in a 63-year-old postmenopausal woman which was misdiagnosed as peripheral nerve sheath tumour (PNST). The case report brings out the operative dilemma and management as the lesion was closely abutting the lower urethra and also highlights the role of immunohistochemistry (IHC) in aiding the diagnosis.

Case presentation

A 63-year-old postmenopausal woman presented with a painless vulval mass which progressively increased in size over a year and led to difficulty in walking. She had no history of fever, vaginal discharge, bowel disturbances and medical comorbidities. There was no difficulty in initiation of urination, incontinence and change in frequency or urgency. Her urinary flow was told to be normal and there was no feeling of incomplete evacuation. There was no history of genitourinary malignancies in the family. Four years ago, she underwent excision of a vulval mass at the same site which was diagnosed as neurofibroma. She had undergone sterilisation after second delivery 40 years ago. No history of any sexually transmitted disease and sexual relations for the past 4 years. She attained menopause at the age of 51 years and has no history of postmenopausal bleeding. Her previous menstrual cycles were regular, lasting for 3 days with normal flow. Her general and systemic examination were unremarkable with no lymphadenopathy. Vulval examination showed a 12×10 cm, tenderand congested firm mass with a smooth surface and well-defined borders involving the clitoris and left labia majora (figure 1A,B). Involvement of superior urethral margin was suspected. Cervix and vagina appeared healthy on speculum examination. Bimanual examination revealed an atrophic uterus with no adnexal lesion. In view of recurrence of the mass, malignancy was suspected, and for confirming the diagnosis and planning the extent of surgery and the preoperative counselling, if malignant, a wedge biopsy was done which was reported as PNST.

Figure 1.

Leiomyoma of the vulva involving the clitoris and labia majora,(A) extending upto urethra. Arrow points towards the urethral orifice (B). H&E stain ×40 magnification (C)—section showing interlacing bundles of smooth muscle cells with elongated vesicular nucleus with moderate pink cytoplasm. No mitosis or necrosis was seen. Immunohistochemistry for smooth muscle actin(SMA) antibody ×40 magnification (D)—the tumour cells are positive for SMA as shown in the figure cytoplasmic positivity and (E) postoperative picture of the perineal region.

Investigations

Imaging (ultrasonographyandcontrast-enhanced CT) showed a vulval exophytic mass (10×8×7 cm) with increased vascularity and without any bony or lymph nodal involvement. It also showed an atrophic uterus having an endometrial thickness of 2 mm and bilateral normal atrophic ovaries. There was no evidence of hydroureteronephrosis in both the kidneys. Her haemoglobin was 98 g/L, blood urea 20 mg/dL, serumcreatinine 0.61 mg/dL, fasting blood sugar 86 mg/dL, postprandial sugar 136 mg/dL and urine culture was sterile. Pap smear was satisfactory and negative for intraepithelial lesions.

Differential diagnosis

Differential diagnoses include haemangioma, PNST, fibroma, angiomyxoma and soft tissue sarcoma. As they may present as a mass in the vulval region, the diagnosis is based on the histopathology and IHC staining. Pattern of spindle cell arrangement seen in PNST mimics the smooth muscle arrangement in leiomyoma; however, on IHC, PNST shows positivity for S-100, CD34 and neuron-specific enolase; leiomyoma is positive for desmin and smooth muscle actin (SMA). Along with histological differentiating features, such as marked blood vessel changes to nuclear atypia and high mitosis haemangiomas, angiomyxomas and soft tissue sarcomas also show positivity to vimentin on IHC.

Treatment

The patient was counselled regarding the risk of postoperative urinary incontinence in view of suspected urethral involvement. She was counselled regarding the need for two-stage operation if she develops incontinence. Wide local excision was performed under spinal anaesthesia. The clitoral prepuce and shaft along with the erectile tissue and the vascular bundles were carefully excised ensuring haemostasis. Resection of the superior urethral margin (5 mm) was also performed with assistance from the urology team. Drain was kept for 3 days. Intravenous antibiotics (ceftriaxone 1 g two times per day and metronidazole 500 mg three times per day) were given for 7 days. Postoperative period was uneventful. After removal of urinary catheter on 7th postoperative day, the patient voided well without incontinence.

Histopathological examination (HPE) showed spindle pattern arrangement of cells with possibility of PNST/leiomyoma (figure 1C). However, further evaluation with immunohistochemical staining was positive for SMA which confirmed the diagnosis of leiomyoma (figure 1D). Review of the wedge biopsy specimen with IHC staining also confirmed the same.

Outcome and follow-up

On follow-up after 8 months, the patient was asymptomatic with no recurrence.

Discussion

Leiomyoma of the vulva, a rare tumour, arises from smooth muscle within erectile tissue, walls of blood vessel, round ligament and erector pili muscle.² Although the age at presentation varies from 15 to 70 years, it is most commonly reported among postmenopausal women. Size of the reported cases varies from 0.5 to 15 cm.³ As noted in our case, very few cases of giant leiomyoma (>10 cm) have been reported in the literature.⁴ Transperineal ultrasound aids in diagnosis but MRI is better to delineate the extent of tumour and to distinguish between benign and malignant tumour.¹

Even though most of them present with a vulval mass, similarities in HPE make the diagnosis difficult. Differential diagnoses include leiomyoma, haemangioma, PNST, fibroma, angiomyxoma, soft tissue sarcomaand so on.⁵ Pattern of spindle cell arrangement seen in PNST mimics the smooth muscle arrangement in leiomyoma. Immunohistochemical markers can help in their differentiation, aiding in diagnosis.⁵ While PNST shows positivity for S-100, CD34 and neuron-specific enolase; leiomyoma is positive for desmin and SMA, as noted in our case. The similar diagnostic dilemmawas reported by Wagay et al and Moraleset al where vaginal leiomyoma and cervical leiomyoma, respectively, were mistaken for schwannoma.^{3 6}

Wide local excision with excision of surrounding normal tissue is the treatment of choice as it reduces recurrence.^{3 7} In a case series on vulval smooth muscle tumours by Nielsenet al, there was 5% recurrence of vulval leiomyoma and they suggested the need for long-term follow-up.⁴ In our case, since the preoperative biopsy was reported as PNST and HPE of the operative specimen was inconclusive, IHC was performed. Staining with SMA, which was reported positive, aided in the final diagnosis. It might be possible that the earlier growth in the same region which was excised 4 years ago, though reported as neurofibroma, could still possibly be a leiomyoma. Since the previous slides were unavailable and no IHC markers were studied, it is difficult to comment on the accuracy of diagnosis and whether this was a case of recurrent leiomyoma which is again rare in this region.

Leiomyomas of the perineal region, similar to uterine leiomyomas, are thought to shrink in size/regress after menopause.⁸ However, few reports suggest that they can recur in the postmenopausal women and can even grow in size in that group, suggesting mechanism other than hormonal in their development.^{8 9} This includes abnormal tissue repair resulting in altered extracellular matrix formation and disordered healing, and a reduced apoptosis secondary to injury from infection/inflammation.¹⁰ These mechanisms may also be the reason for recurrence, even though extremely rare, in postmenopausal women.

Recurrent large leiomyoma involving the clitoral region and lower urethra can be tricky to manage and require a multidisciplinary approach with operative assistance from urologist and excision of lower urethra to prevent recurrence. Immunohistochemical examination, as in the index case, will aid in the differentiation between various soft tissue tumours affecting the vulval region. Long-term follow-up is advisable as recurrence is reported in such cases.

Learning points.

• Immunohistochemical examination will aid in the differentiation between various soft tissue tumours affecting the vulval region.

• Recurrent large leiomyoma involving the clitoral region and lower urethra can be tricky to manage and require a multidisciplinary approach with operative assistance from urologist and excision of lower urethra to prevent recurrence.

• Wide local excision with excision of surrounding normal tissue is the treatment of choice as it reduces recurrence.