Introduction

From the literature earliest description of an accessory cavitated uterine mass (ACUM) was given by J.Oliver in the year 1912 when he described a patient presenting with dysmenorrhoea who underwent surgical excision of a tumor from the broad ligament, which was described as "a globular-shaped closed sac, containing chocolate-colored fluid, thick-walled and lined by cuboidal epithelium, which resembled very closely the stroma of normal endometrium".^[1] However, throughout the last century, there are not many descriptions regarding this entity until the last two decades, and only occasional case reports have been found throughout the literature. In 2010 P Acién and colleagues described this entity in a case series format^[2] and again in 2012 described this entity as accessory cavitated uterine mass (ACUM) and also discussed this entity's management and origin and pathology subsequent review of case reports.^[3] Since the last decade, ACUM has been more recognized myometrial pathology, probably because of increasing awareness among the surgeon and improved imaging technologies that can recognize more of these cases. ACUM has been considered a cause of dysmenorrhoea, especially in young women, and thus young women presenting with severe dysmenorrhoea often with deterioration of the quality-of-life ACUM should be considered. However, there is no known prevalence of this disease, especially in young women, as we can only find the case reports of these entities, and there are no prospective studies to know the incidence or prevalence of the disease. ACUM also can be called 'accessory cavitated uterine malformation' as this truly represents congenital developmental abnormality and omits the negative connotation that the word 'mass' processes. However, the word 'accessory cavitated uterine mass' is more popular; hence we used it. Here we will describe some of these cases we encountered in our practice in recent years and then a short review regarding various aspects of ACUM. ([Figure 1])

Epidemiology

Most of the pieces of literature regarding ACUM are based on the case series and case reports, so the exact characteristic population is not well-defined. Due to the scarcity of cases, the precise prevalence of this condition is not determined. Not only due to the scarce condition but also lack of awareness among the clinicians, we often miss the diagnosis of ACUM. Most authors proposed that ACUM can be recognized only in a nulliparous young woman aged less than 30 years presenting dysmenorrhoea.^[2], ^[3], ^[4], ^[5] Although most of the cases found are in women less than 30 years of age, there have been reports that ACUM can also be found in more advanced ages.^[3], ^[6], ^[7], ^[8] Patients with ACUM do not always need to have dysmenorrhea. ACUM can be seen in asymptomatic women diagnosed incidentally and may have other symptoms like dyspareunia. This condition is probably present in every population, and lack of awareness is perhaps the reason for the low number of diagnosed cases other than the condition's rarity. On reviewing the literature, this condition is more commonly diagnosed in the Japanese population probably due to the excellent awareness of the clinicians in Japan rather than a genuinely increased prevalence of the condition within this population.^[5], ^[9], ^[10], ^[11], ^[12], ^[13], ^[14]

Aetiology

There are two theories regarding ACUM development: ^[1] an isolated Müllerian duct malformation or^[2] dysfunction of the female gubernaculum. According to the first theory, there is duplication or persistence of an isolated Müllerian duct segment at the level of the attachment of the round ligament. The gubernaculum is composed of muscular fibers that probably derive from the abdominal wall, and when it is fixed and fused with the Müllerian ducts, it grows over the Müllerian ducts. Above this, the Müllerian ducts will give origin to the fallopian tubes, whereas the Müllerian ducts form the normal uterus medially at the point of insertion of the gubernaculum. Sometimes an isolated or duplicated Müllerian part may present here and can give rise to ACUM. Due to gubernaculum malfunction, migration and fusion of the Müllerian segment may remain incomplete and give rise to ACUM. Probably this may be the reason ACUM seats underneath round ligament.^[2], ^[3], ^[15]

Nomenclature

What we describe as accessory cavitied uterine mass (ACUM) is certainly not a new entity, although, in the last decade, it has been more commonly recognized by this name. In the previously published literature, various names were used, as shown in [Table 1]. In 2010, Acién et al. reviewed the literature to determine how many published cases represented true ACUMs according to their proposed criteria, and since then, ACUM has been a more popularised name. Accessory cavitated uterine malformations are also proposed by some authors^[8] as so it more suits as the condition persists from birth as a malformation^[16] and also indicates the benign nature of the condition and omits the negative connotation that the word 'mass' as a matter of fact for some patient term 'mass' may add extra stress on them.

Clinical Presentation

Approximately 7% of young women have an anatomical abnormality in their reproductive tract; the most frequent symptom of this is intolerable pain.^[35] In the review of our cases, although the commonest presentation of the ACUM is dysmenorrhoea, they can also present with dyspareunia, dyschezia, and also there may be other pressure symptoms. Moreover, many patients may be asymptomatic and may be found incidentally during diagnostic hysterolaparoscopy for other indications such as infertility and pelvic pain. On reviewing the published literature, there is no doubt that the most common presentation of ACUM is dysmenorrhoea.^[2], ^[3], ^[7], ^[8], ^[13], ^[14], ^[17], ^[20], ^[24], ^[36], ^[37], ^[38], ^[39], ^[40], ^[41] The pain is usually felt in the ipsilateral site or the central pelvic area, especially during menstruation, and may also proceed the days before menstruation and may be accompanied by chronic pelvic pain.^[2], ^[3], ^[8], ^[29], ^[36], ^[37], ^[41], ^[42] Functional endometrial lining present in the accessory uterine cavity causes secretion of menstrual fluid during the period, and as the secreted fluid is placed in an enclosed space; it gets accumulated during the menstrual time, which during surgery we found as chocolate material inside the mass and chronic accumulation of this fluid leads to increased pressure within the cavity, and subsequent stretching of the cavity which produces pressure effect on the nerve fibers that are causing the pain and chronic stretched out cavity is the reason for having chronic pelvic pain. However, often pain persists and increases during or even after the onset of menstruation.^[3], ^[9], ^[10], ^[13], ^[20], ^[21], ^[27], ^[28], ^[36], ^[37] other symptoms reported by the patients diagnosed with ACUM are dyspareunia,^[2], ^[5], ^[40] dyschezia,^[12], ^[25], ^[40] and hypogastric pain,^[2], ^[3], ^[36], ^[37] but there is clear uncertainty regarding whether ACUM is the sole reason for these symptoms.

We do not have many descriptions regarding asymptomatic ACUM, but this population certainly does exist, as we have found in one incidental case of ACUM diagnosed during an infertility evaluation. ACUM can also be incidentally diagnosed during routine scanning done in pregnancy.^[8] No published literature mentions ACUM associated with infertility or heavy menstrual bleeding. Probably ACUM will not cause infertility as the endometrial cavity is normal in women with ACUM. Although ACUM is most commonly diagnosed in nulliparous women, it can also be found in parous women.^[3], ^[31], ^[43], ^[44] Although it is challenging to suspect ACUM on clinical examination, some authors have described the woman who had a diagnosis of ACUM had present with clinically palpable, a tender mass that can be felt on abdominal on bimanual examination, and often this case mistaken as fibroid, endometrioma or ovarian cyst.^[2], ^[12], ^[13], ^[25]

Investigations and Diagnosis

Diagnosis of ACUM is based on the assessment of uterine morphology, which can be done preoperatively by non-invasive diagnostic methods like ultrasound and MRI. Intraoperative assessment of uterine morphology is the definitive way of diagnosis and treatment, although it is invasive and not without complications. Postoperative assessment of tissue by histopathological examination adds up the icing to the diagnosis.

HSG, SIS and HyCoSy

In the past, many authors proposed that to diagnose ACUM, one should rule out the abnormal uterine cavity and congenital uterine anomaly and establish the non-communicating nature of the lesion. Thus they used hysterosalpingography (HSG), Hysterosalpingocontrast-sonography (HyCoSy), or saline infusion sonohysterography (SIS), which are well popular methods to establish normal uterine cavity and fallopian tubes.^[2], ^[3], ^[5], ^[7], ^[10], ^[11], ^[12], ^[13], ^[17], ^[23], ^[42] We do not use such methods in our practice.

Assessment of intraoperative uterine morphology

Diagnostic hysterolaparoscopy is one of the optimal modes of diagnosis and treatment for patients with ACUM. In most cases, ACUM appears as a fibroid-looking mass from the outside. An ACUM appears as an asymmetrical uterine bulge on the anterolateral aspect of the uterus caudal to the insertion of ipsilateral round ligament and cranial to the cervico-isthmic junction or insertion of the uterine artery and classically contains altered collected blood secreted from the functional the endometrium lined inside the cavity which appears as a chocolate color fluid on opening the cavity.^[2], ^[3], ^[7], ^[15], ^[37] Although hysteroscopy is not necessary for ACUM, it helps us to know whether the endometrial cavity is normal or not and rules out any presence of communication, and also rules out any obstructive causes of Mullerian anomaly. In our experience, intraoperative diagnosis of ACUM can be made by its characteristic location and morphology.

Diagnosis of ACUM is often delayed as we think delayed ACUM in women in dysmenorrhea is probably due to a lower incidence of ACUM. This is evident by the fact that many documented cases of ACUM published in the literature were undergone diagnostic laparoscopies that failed to diagnose ACUM.^[2], ^[19], ^[28], ^[53] Even on laparoscopy (or sometimes on laparotomy) ACUM one may find it difficult to diagnose^[11] as from the outside, it often looks like a fibroid (although characteristically placed), and the hysteroscopy cavity will be perfectly normal, so the clinician should actively look for ACUM, especially in young nulliparous women with dysmenorrhea. Sometimes intraoperative ultrasound can be useful to locate ACUM successfully and aid excision from a normal uterus.^[8], ^[10], ^[11], ^[52]

Histology

Macroscopically excised specimens of ACUM have a uterus-like organization with a central cavity lined by endometrium with hemorrhagic content surrounded by myometrial tissue similar to the myometrium of a healthy uterus.^[13], ^[36], ^[53]

On microscopic examination cavity of ACUM is lined by an endometrial gland and stroma. Similar to normal endometrium, they also positively stain for CD10, estrogen receptors (ER), and progesterone receptors (PR).^[5], ^[36]

Often we can get reports of focal adenomyosis in the resected specimen of ACUM.^[2], ^[3], ^[5], ^[10], ^[14] This is due to prolonged blood collection within the cavity causing adenomyotic changes.

The condition may be confused with cystic adenomyosis, where the cysts are usually quite small and do not possess a typical endometrial lining or uterus-like muscle, as seen in ACUM. Although there are no definitive criteria to differentiate ACUM from cystic adenomyosis, well ordered concentric organization of smooth muscle fibers seen in ACUM can differentiate them from cystic adenomyosis, where the smooth muscle fibers are disorganized.^[36], ^[53] The main uterus does not possess features of adenomyosis, but the myometrium of ACUM may show features of adenomyosis.

Key to Diagnosis

Diagnosis of ACUM often remains challenging, possibly because it is not a common clinical condition we often encounter daily in our clinic. Even with the advancement of ultrasonography, including 3D ultrasonography and MR imaging, there remains diagnostic confusion regarding ACUM. Usually, during surgery, intra-operative uterine morphology assessment is sufficient enough to diagnose ACUM, and corresponding histopathological findings add up value to the diagnosis. Often a high index suspicion is necessary to diagnose the case of ACUM. Whenever a young and nulliparous patient presents with severe dysmenorrhoea primarily affecting her quality of life, one should add ACUM to the bucket list of their differential diagnosis. Important diagnostic indications are given in [Table 3] that we used in our practice.

Differential Diagnosis

Clinicians often find the diagnosis of ACUM a challenge, possibly due to unfamiliarity with the condition, and it is better to keep this on the bucket list of differential diagnoses when young women present with severe dysmenorrhea. Differential diagnosis of ACUM includes non-obstructive congenital uterine anomaly such as unicornuate uterus with rudimentary horn or Robert's uterus, subserosal fibroid or degenerated fibroid, cystic adenomyosis, congenital uterine cyst or myometrial cyst, and ovarian endometrioma.

Treatment

Various treatment options are available for ACUM, ranging from simple analgesia to complete surgical excision.^[8] According to the most published literature, ACUM is diagnosed chiefly based on its symptoms and is usually treated by surgical management but also other modalities of management such as expected management, medical therapies, and sclerotherapy can also be possible. We prefer surgical excision of ACUM from the normal uterus in our practice.

Surgical Excision

In our experience, surgical management of ACUM is the primary mode of treatment as it completely excises the lesion, and all the secondary symptoms caused by the ACUM, such as dysmenorrhea, immediately disappear after the surgery. All published cases of surgery of ACUM have reported almost complete resolution of secondary dysmenorrhea due to ACUM soon after surgery^[2], ^[3], ^[5], ^[36], ^[53] and remain pain-free until follow-up completion,^[4], ^[9], ^[17], ^[32], ^[42], ^[6] which makes excision of ACUM a definitive treatment. Excision can be performed both via laparotomy and laparoscopically.

Laparotomy has all the advantages of open surgery, including quick and easy access. Furthermore, there is greater surgical precision in open surgery, and although ACUM has no definitive plane of dissection in open surgery, better enucleation of ACUM is feasible. Also, complete excision can be performed without spillage of its contents. Moreover, due characteristic location of ACUM, it is close to vital structures like the uterine artery, urinary bladder, and endometrial cavity. Therefore, surgical excision without disturbing other structures is crucial, especially in young women. Acién et al.^[2], ^[3] described cases of ACUM managed via laparotomy either by excision of ACUM or by hysterectomy for women with a separate indication of hysterectomy.

Laparoscopic excision of ACUM has been favored by many surgeons compared to open surgery because it has the advantages of quicker recovery with reduced postoperative pain, reduced incidence of abdominal adhesions, and also moreover less scar over the abdomen, especially in young women. Most authors believe that sufficient precision in enucleation or excision of ACUM can be managed laparoscopically without difficulty due to the availability of good energy source devices and neat and clean visualization during laparoscopy and fine dissection instruments.^[6], ^[17], ^[58], ^[59], ^[61], ^[62], ^[63]

We like to perform hysteroscopy before proceeding to laparoscopy to know the normal uterine cavity and rule out any communicating Mullerian anomaly.

Vasopressin infiltration into the uterine–ACUM junction sub-serosal interface to aid with hemostasis has been reported by most authors performing laparoscopic excision.^[5], ^[7], ^[10], ^[11], ^[13], ^[14], ^[17], ^[18], ^[42], ^[44], ^[59], ^[63], ^[64] We also, in our practice, use vasopressin infiltration not only to reduce hemostasis but also to enable easy dissection.

Dividing the round ligament to gain access to the ascending branch of the uterine artery reduces the risk of unintentional injury, had been proposed some authors.^[5], ^[21], ^[21], ^[36], ^[65] We do not think it is always required unless ACUM is too big and adhesions surround it.

Dissection of the ureterovesical fold has also been mentioned to facilitate safe access to the laterally placed ACUM.^[65] But to our experience ACUM usually places cranial to uterocervical fold, and often there is no requirement of performing this extra step.

The overlying serosa and myometrial plane can be incised with a cold knife^[9], ^[13], ^[14], ^[17] and monopolar energy source.^[4], ^[5], ^[6] We prefer to use a scissor for dissection as we do not know the extent of thermal damage, which can inadvertently injure normal endometrium. A bipolar energy device can also be used. Dissection devices should be chosen based on the surgeon's preference and comfort.

ACUM excision or preferably enucleation should be performed circumferentially along the ACUM–myometrial interface. In contrast to a myomectomy, where dissection advances along a pseudocapsule, no definitive dissection plane can be found, indicating that ACUM is a congenital malformation.^[3], ^[24]

As the boundaries of an ACUM are unclear, intraoperative ultrasound has been described to facilitate delineation of the lesion and to aid excision by some authors.^[13], ^[53], ^[66] Intraoperative ultrasound can also help to avoid inadvertent breach of the uterine cavity. Peyron et al.^[36] illustrated in their paper that the mean distance of the ACUM from the uterine cavity was 6 mm on MRI, and one can be breached into a normal endometrial cavity during surgical excision, which can have subsequent consequences such as the formation of intrauterine adhesions, development of adenomyosis, especially in young women. We also often perform an intraoperative pelvic ultrasound after excision of ACUM.

Few authors had described the intraoperative assessment of the integrity of the normal uterine cavity post-excision using methylene blue dye chromopertubation.^[20], ^[32], ^[36], ^[65] We think performing a dye test before excision is also good enough as it demonstrates normal uterine cavity and bilateral tubal patency, and also, in cases of women having infertility simultaneously can establish tubal patency. Nevertheless, there is no evidence that ACUM in any way can cause infertility.

ACUM is considered a benign lesion, so most likely, there will not be any recognized hazard due to spillage of its contents. In some of our cases, there was a spillage of contents during dissection, and on follow-up till now, no recognized complications so far from this.

Various techniques have been described for specimen retrieval, including the use of colpotomy,^[5] morcellation^[10], ^[11], ^[17], ^[24], ^[64] and specimen retrieval in endo bags.^[7], ^[18], ^[53], ^[65] We mostly used power morcellation with or without an endo bag to retrieve the excised tissue.

Sclerotherapy

Sclerotherapy is an option for women who do not want to undergo surgery as their primary mode of treatment. The transvaginal ultrasound-guided aspiration and use of sclerotherapy for the treatment of ovarian cysts, including endometrioma, have gained popularity recently.^[67], ^[68]

The principle of use of sclerotherapy remains the same whether it is for an ovarian cyst (endometrioma) or in cases of ACUM. Sclerotherapy is the therapeutic use of sclerosants that causes controlled destruction of undesired target tissues such as the endometrial lining of the accessory uterine cavity.^[69] Sclerosant agents (ethanol, ethanolamine oleate,  hypertonic such as saline, glucose, etc.) destroy the cavity lining, resulting in inflammatory changes and subsequent fibrosis of the endometrial lining with eventual obliteration of the accessory cavity.

Merviel et al. first described the use of ethanol sclerotherapy in a case diagnosed with ACUM.^[70] In the study by Naftalin et al., four patients chose to have sclerotherapy and had sufficient pain relief on follow-up.^[53] But later, half of them had a recurrence of secondary symptoms and underwent surgical management.

Transvaginal sclerotherapy is usually performed under general anesthesia and continuous ultrasound guidance. Usually, an 18 gauge needle is used under continuous ultrasound guidance after puncturing through the anterior vaginal wall, and then through a myometrial mantle needle is inserted into the cavity of the ACUM. First, a small amount of the intracavitary fluid is taken out and sent for cytopathological examination, and the remainder of the fluid is also drained out. Next, a sclerosant agent like 99% ethanol is installed in the cavity under ultrasound guidance, and the needle is withdrawn carefully.

Ethanol sclerotherapy can avoid uterine scarring and the secondary risk of uterine rupture.^[70] Moreover, it avoids all the risks of major surgery. However, there is the risk of inadvertent leakage of sclerosant agents installed in the peritoneum.^[68] This is a recognized complication in alcohol installation for ovarian endometrioma, possibly due to thin walls, but it is less likely in the case of ACUM, which is surrounded by thick myometrium. Certainly, ethanol sclerotherapy has a highly variable recurrence rate, and the risk of recurrence is higher in women treated with ethanol washing than in ethanol retention.^[68]

We currently do not use sclerotherapy in our practice, but certainly, this is an option for women with ACUM who do not want to have surgery. But they should be counseled that this is not a curative procedure, and there are variables risk of recurrence of the symptoms and may need another intervention in the near future.

Follow-Up

Currently, limited data is available to guide the patients with ACUM for follow-up. In our practice, we usually follow up one week after the surgery and then again at three months and 6 months with a pelvic ultrasound to see whether there is a recurrence of pain or not. As with most patients being young, follow-up is especially required for this group to know whether there is any effect on infertility and pregnancy.

Conclusion

ACUM is a recognized Mullerian anomaly that is habitually located underneath round ligament, with an unknown prevalence; that is probably related to a dysfunction of the female gubernaculum and is often underdiagnosed or commonly misdiagnosed as fibroid or obstructed cavitated rudimentary horn with unicornuate uterus due to a lack of knowledge and awareness about ACUM. ACUM is a less rare condition than previously believed; hence ACUM diagnosis is essential in clinically suspicious cases. With a high index, clinical suspicion, and an appropriate diagnostic tool such as ultrasound and MRI, ACUM can be diagnosed. Laparoscopic surgical excision is the definitive treatment for ACUM as it is a benign condition. Further studies are required, especially a prospective study, to know their long-term effects on women's health, heavy menstrual bleeding and infertility, and whether surgical excision has any long-term consequences.

Source of Funding

None.

Conflict of Interest

None.