Aggressive angiomyxoma presenting as an ischiorectal fossa tumour

Abstract

This is a case of a young healthy woman who presented with left groin pain. On work-up, she was found to have a large, well-defined mass in the ischiorectal fossa with a percutaneous biopsy of only a benign mesenchymal mass. A multidisciplinary team of surgeons (ie, colorectal, orthopaedic, vascular and urological surgery) collaborated in planning and performing the extirpation of the tumour. Final histopathology identified the tumour to be an aggressive angiomyxoma, a benign tumour with a high predilection for local recurrence. The patient had an uneventful postoperative course, with maintenance of good functional status.

Background

The ischiorectal fossa (IRF), while an anatomical region that is well-studied for cases of infection, is an unusual site of primary tumours. A tumour in the IRF often presents with asymmetry of the gluteal area and left pelvic pain. Due to the rarity of the disease, diagnosis is often difficult to make and standard management is elusive.¹

Several case reports and a case series have been published on IRF masses. All concluded that prompt diagnosis using dependable imaging followed by swift management are important.²

Case presentation

A healthy 26-year-old woman experienced severe left groin pain that prompted consult at the emergency department. She was treated with analgesics and advised CT stonogram for the impression of urinary tract stone. This showed a 10.4×8.5×5.3 cm lobulated mass (HU +26 to +32) in the left pelvis extending down to the IRF. The patient was then lost to follow-up.

On initial consult at our clinic a year later, a MRI of the pelvis was requested. This showed an interval increase in size of the left hemipelvic mass to 12×11×6 cm, still within the IRF that caused displacement of the uterine cervix, anorectum and urinary bladder towards the contralateral side. It was noted to be isointense to muscle on T1 weighted, hyperintense on T2 weighted (T2W), with curvilinear hypointensities within and exhibited heterogeneous enhancement.

After discussion in a multidisciplinary meeting, she was advised to undergo a CT-guided biopsy for tissue diagnosis. Neoadjuvant treatment was contemplated should the biopsy return as a malignancy with good response to either chemotherapy, radiotherapy or both. The result was a mesenchymal lesion with no atypical histomorphological features. Immunohistochemical stains were consistent with myofibroblastic proliferation but no final tissue diagnosis could be given.

Given the benign pathology and uncommon location, open surgery was planned and executed in anticipation of limited space. It was led by a colorectal surgeon assisted by an orthopaedic surgeon, vascular surgeon and urologist. We did preoperative cystoscopy, bilateral ureteral stenting, endoanal ultrasonography, exploratory laparotomy, osteotomy of left pubic ramus and excision of IRF tumour.

The patient was placed under combined general endotracheal and epidural anaesthesia. She was then positioned in dorsal lithotomy. Preoperative cystoscopy showed extrinsic compression of the left side of the bladder up to the ureteral orifice (figure 1). Both ureteral stents were inserted with ease.

Figure 1.

Preoperative cystoscopy. On cystoscopy, there was note of external compression on the left side of the urinary bladder. No intravesical lesions were appreciated. PGH, 2019.

While on lithotomy, endoanal ultrasonography was done to document the degree of involvement of the anal sphincters. This showed a distinct hypoechoic mass on the left that was closely related to the external anal sphincter (figure 2).

Figure 2.

Endoanal ultrasonography. Endoanal ultrasonography showed the mass to be in close proximity to the EAS. There was, however, no actual invasion of the anal sphincters, and a plane of differentiation was still maintained. PGH, 2019. EAS, external anal sphincter; M, mass.

As discussed in the multidisciplinary meeting, a laparotomy incision will give more direct access to the mass as opposed to a posterior approach. The team proceeded with an infraumbilical laparotomy to enter the abdomen. After the sigmoid and rectum were mobilised in a lateral-to-medial manner, a soft, doughy, fibrous mass was encountered at the level of the pubis (figure 3). It was closely related to the urinary bladder, vagina and rectum.

Figure 3.

Identification of the mass. The mass was anterolaterally located and was very distinct with its soft and fibrous character. PGH, 2019. M, mass.

As expected, the laparotomy approach was formidable because of the limited space afforded by the rigid pelvic cavity. A 3 cm segment of the superior pubic rami was osteotomised by the orthopaedic surgeon to be able to expand the pelvis with retraction (figure 4). This allowed better visualisation and access down into the pelvis. Sharp dissection of the mass from the bladder, rectum, vagina and pelvic sidewall was done with due care not to violate any of these structures. The specimen is shown in figure 5.

Figure 4.

Osteotomy of the left pubic ramus. A 3 cm osteotomy of the pubic ramus allowed for a wider working space, and better visualisation of the ischiorectal fossa tumour and adjacent structures. PGH, 2019. O, osteotomy, lateral end.

Figure 5.

Specimen. The smoothly lobulated 16×10 cm mass with a bilobed inferior pole was removed whole from the ischiorectal fossa. PGH, 2019. A, anterior; I, inferior; P, posterior; S, superior.

Investigations

CT and MRI have been useful for evaluation and diagnosis of the IRF. Radiologists have a preference for MRI given its superior tissue contrast and multiplanar capabilities. Furthermore, MRI provided better delineation of the muscular structures in the pelvis, and their relationship to the lesion. Both may be employed in identification, staging and surgical planning of the processes affecting the IRF.³

Primary neoplasms in the IRF include lipomatous tumours, aggressive angiomyxoma, vascular lesions and neurogenic tumours. Simple lipomas are characterised by homogeneous, circumscribed fat without enhancing solid component. Mixed fat and solid lesions raise a suspicion for liposarcoma. Angiomyxoma is a soft tissue mass that commonly presents as a large mass that smoothly displaces perineal tissues with its myxomatous or ‘swirled’ content. Haemangiomas are primary vascular lesions that appear bright on T2W MRI with multiple slow flow vessels with phleboliths. Peripheral nerve sheath tumours are generally benign. Both subtypes of neurofibroma and schwannoma are bright on T2W MRI but will enhance after contrast administration. They may often present with a ‘target sign’ but absence of which raises the suspicion of malignancy.⁴

While the lesions have distinct appearances on imaging, Buch et al recommend percutaneous biopsy for tissue diagnosis. This is very important in prognostication and determining the risk for malignancy is essential in planning the surgical approach. A diagnosis of malignancy may also allow for the consideration of neoadjuvant treatment for tumours that are unresectable, or alternative modalities for inoperable patients.

Our patient presented with a large, well-defined IRF mass, with interval increase in size to 12 cm. The CT and MRI showed that the mass was isodense with muscle fibre (figure 6). On T2W images the mass was also distinct, which suggested its stromal content. Also, on T2W images, there were curvilinear hypointensities and general heterogeneous enhancement showing heterogeneity of the specimen. The addition of endoanal ultrasonography to the battery of imaging studies gave a real time assessment of the status of the external anal sphincter right before resection.

Figure 6.

MRI. This is axial and coronal views of the 12×11×6 cm mass that is isointense to muscle on T1 weighted, hyperintense on T2 weighted with curvilinear hypointensities within, and exhibits heterogeneous enhancement. PGH, 2019.

The tissue diagnosis with percutaneous biopsy could only provide a supporting proof of a benign mesenchymal lesion, probably myofibroblastic in origin.

In literature review, there is a variety of histopathology for primary IRF tumours. During the initial biopsy before the surgery, diagnosis was a myofibroepithelial lesion because of the following stains:

• Ki-67: nuclear staining in less than 1% of tumour cells.

• Desmin: moderate cytoplasmic staining in 10% of tumour cells with focal areas of up to 20% staining.

• S100: negative in tumour cells.

• CD34: negative in tumour cells.

Ki-67 identifies actively proliferating cells. Desmin stains intermediate filaments in striated muscles. S100 stains calmodulin and troponin C and is thus present in schwannomas, ependymomas, astrogliomas and melanoma. CD34 stains intercellular adhesion proteins in haematopoietic progenitor and endothelial cells.⁵

After the surgery, the pathologist examined the specimen and found low grade spindle cell lesion present in the cauterised margins. The diagnosis was narrowed to a deep aggressive angiomyxoma or a low grade myofibroblastic tumour using the following stains:

• SMA: focally positive in tumour cells.

• H-caldesmon: negative in tumour cells.

• MDM2: negative in tumour cells.

SMA identifies cells of smooth muscles and myofibroblasts in normal, reactive and neoplastic tissue. H-caldesmon differentiates smooth muscles from myofibroblasts by binding calcium, calmodulin, tropomyosin and actin. MDM2 stains malignant lipomatous lesions. After a positive result in staining with oestrogen and progesterone receptor (ER/PR), the final diagnosis was aggressive angiomyxoma.⁵

Aggressive angiomyxoma is a mesenchymal tumour first reported by Steeper and Rosai.³ It builds on the findings of Virchow that myxoma and myxomata are soft tissue tumours that resemble tissues normally found in the umbilical cord. Angiomyxoma are described to have sparse population of spindle fibres distributed in a loose myxoid stroma. ‘Angio’ was added to emphasise the presence of prominent vascularity with widely dilated vessels with thickened muscular layers. ‘Aggressive’ was used to depict the highly recurrent behaviour seen in four of their nine reported patients.⁶

Aggressive angiomyxoma is a rare pelvic tumour often diagnosed as a protuberant vulvar or perineal mass.⁷ As it grows, it presents with pelvic fullness, perineal swelling, pain and bowel and bladder habit changes often in young females of reproductive age. It is often clinically mistaken as a Bartholin cyst, vaginal abscess, leiomyoma, lipoma and, inguinal, perineal or femoral hernia. Radiologically, it is a well-defined mass that is hypodense to muscle and is predominantly cystic with solid components. It is often seen displacing rather than invading nearby organs. Histologically, it presents as a scant or bland myofibroepithelial lesion in a myxoid stroma with a strong reactivity to ER/PR staining, highly suggestive of hormonal influence in growth and regulation.⁸

Treatment

Surgical resection with clear margins is the mainstay management for aggressive angiomyxoma.⁹ The handful of cases reported employed several surgical approaches, depending on the surgeon’s preference as long as the margin was clear on histopathological examination. Despite wide excision, recurrence can be as high as 72% in 2–4 years after surgery. As high as an 85% recurrence rate in 5 years has been documented.² MRI is a recommended modality for surveillance as early as 6 months after surgery. There have been reports of adjuvant therapy with radiation and hormonal treatment with gonadotropin releasing hormones and selective ER modulators with varying results. Some authors advocate just continuous surveillance due to its indolent course.

We did a multidisciplinary approach through an abdominal incision for several reasons: (1) the absence of grossly apparent tumour in the perineal area, (2) the bulk of the tumour was located in the abdominal area and (3) the need for greater exposure provided the size of the mass. Despite such an advantage, pelvic dissection was formidable because of the space limited by the pelvis, especially the rami. Orthopaedics provided a planned osteotomy of the left pelvic ramus to widen the area. They did a 3–4 cm excision to break the solid rim that opens to the field of operation. The mass was sharply dissected and removed with visualisation from the abdominal incision and the patient had an unremarkable postoperative course.

The final histopathology report was important in determining the tumour we dealt with and in assessing the margin. Aggressive angiomyxoma already has a propensity for recurrence and given the finding of the lesion in the cauterised margins, close follow-up and work-up is prudent.⁹

Outcome and follow-up

The patient tolerated the 8-hour procedure well, with a 400 mL blood loss. No blood products were transfused. The postoperative course of the patient was uneventful. She was discharged on the fourth postoperative day. On her latest follow-up at 3 months postoperatively, she had intact sphincter function and is able to ambulate well.

Discussion

The IRF is a familiar territory for colorectal surgeons as this is often encountered when managing abscesses and fistulas.¹ It is the largest space of the anorectal region, and is defined superiorly by the levator ani, medially by the external sphincter muscles, laterally by the obturator fascia, anteriorly by the superficial and transverse perineal muscle and inferiorly by the skin of the perineum as shown in figure 7. It contains adipose, nerves, blood and lymph vessels and the pudendal nerves.

Figure 7.

The ischiorectal fossa (IRF). The boundaries of the IRF are shown in axial and coronal views illustrated by Cabanilla-Manuntag. The IRF is the largest space in the anorectal region bound by the obturator internus (O) anteriorly, pudendal canal (PC) laterally, urogenitalia (U), external sphincter and anococcygeal ligament (A) medially, and line from the anococcygeal ligament to the gracilis muscle (GM) posteriorly. Superiorly, it is bound by the levator ani (L). [Adapted from Arbelo-Cruz et al¹(https://cme.lww.com/files/AnatomyandPathologyoftheIschiorectalFossa-1469135755878.pdf)].

Primary tumours in the IRF are few. On PubMed search of ‘angiomyxoma’ and ‘ischiorectal fossa’, only eight articles came up. The summary of case reports is listed in table 1. They describe 16 cases, 87.5% of which are women, aged 25–65 years. All were treated with surgery with acceptable surgical outcomes.

Table 1.

Reported aggressive angiomyxoma in the ischiorectal fossa in PubMed

Author	Age	Gender	Symptom	Management	Postsurgery outcome	Follow-up	Recurrence
Dalvi et al10	60	F	Right gluteal swelling	Surgery	R0	Not available	Not available
Kanao et al11	46	F	Vulvar mass	Surgery	R0	12 months	None
Buchs et al4	38	F	Gluteal mass	Surgery	R0	12 months	After 4 months
Buchs et al4	25	F	Perirectal fullness	Surgery	R0	24 months	None
Rotmensch et al12	43	F	Left labial swelling	Surgery+hormonal therapy	R1	6 months	6 months
Rotmensch et al12	32	F	Labial mass	Surgery	R0	4 months	4 months
Rotmensch et al12	33	F	Obturator hernia	Surgery	R0	30 months	None
Rotmensch et al12	42	F	Perineal hernia	Surgery	R0	30 months	None
Rotmensch et al12	40	F	Cervical mass	Surgery	R0	14 years	14 years
Rotmensch et al12	32	F	Levator sling hernia	Surgery	R0	12 months	None
Rotmensch et al12	35	M	Groin mass	Surgery	R0	13 months	None
Rotmensch, et al12	38	F	Labial mass	Surgery	R0	Not available	Not available
Rotmensch et al12	47	F	Perineal hernia	Surgery	R0	12 months	12 months
Rotmensch et al12	53	F	Perineal hernia	Surgery	R0	36 months	36 months
Abu et al13	46	F	Left vulvar swelling	Surgery	R0	6 weeks	None
Hastak et al14	65	M	Left perineal swelling	Surgery	R0	Not available	Not available

Learning points.

• Ischiorectal fossa tumours are rare primary lesions of the pelvis and its rarity leads to common difficulty in diagnosis and management.

• This case illustrated that management should be by prompt diagnosis through imaging and biopsy, treatment planning with a multidisciplinary team and wide excision with clear margins, to improve the outcomes.

• With a final diagnosis of aggressive angiomyxoma, a benign tumour but with a high rate of local tumour recurrence from previous reports, we strongly recommend close follow-up and surveillance with CT scan and MRI.