Obturator Hernia

Etiology

The obturator foramen is an opening in the pelvis created by the ischium and pubis bones. The foramen itself is covered by a quadrella musculoaponeurotic membrane – the obturator membrane. The neurovascular bundle (obturator artery, vein, and nerve) pierces this membrane anterosuperiorly, then passes through the obturator canal. The obturator canal starts as the obturator groove, becoming the obturator canal by a ligamentous band attaching to the posterior and anterior obturator tubercle. This canal connects the pelvis to the medial compartment of the thigh. The obturator canal is about 0.2 to 0.5 cm wide, and 2to 3cm long.[6] The obturator nerve is the most cranial of the neurovascular bundle passing through the canal. It subsequently then divides upon exiting the canal into an anterior and posterior division. 

The obturator membrane is covered on either side by the obturator muscles. As such, any hernia that forms will pass through obturator internus, the obturator membrane, and obturator externus in that order. The natural location for the hernial sac to lie after its passage through these structures is deep and inferior to the pectineus muscle, superficial to obturator externus. However, the hernia could protrude through the obturator externus muscle, taking with it the posterior obturator nerve. In this position, the hernial sac lies posterior to the adductor brevis. Very rarely, the hernial sac can be found between the obturator internus and externus muscles.

The obturator foramen has a different shape according to the sex of the individual. Women tend to have triangular, wider foramina, while men tend to have more oval ones.

Epidemiology

Obturator herniae are called ‘the skinny old woman hernia’. This is due to the high incidence of these herniae in women in their seventh or eighth decade, who are normally gaunt (8), and indeed it can almost be said to be found almost exclusively in women.[1][7] As alluded to before, this might be explained by the different shape of the obturator canal in women – having a wider transverse measurement, that is more obliquely placed, thus allowing for the easier passage of the hernial contents. Multiparity may also lead to structural changes in the tissues, allowing for an obturator canal that is more likely to expand and allow for herniation through it.[8] Bilateral obturator herniae are rare, possibly due to the presence of the sigmoid colon on the left.[9][10]

History and Physical

Obturator hernias are rarely diagnosed in a non-symptomatic patient, with the majority of cases presenting as an emergency with intestinal obstruction (see Image. Intestinal Coil).[1][6][7][11] The presentation of a strangulated obturator hernia is rare, with it being less than 0.04% of all hernias.[12] However, in an emaciated elderly female presenting with intestinal obstruction, this should be considered as a possible diagnosis. This is especially so in the case of a virgin abdomen in this population – thereby raising suspicion of a cause other than adhesions.

The intimate relationship of the hernia with the obturator nerve could lead to the presence of the Howship-Romberg sign. This is obturator neuralgia, causing pain in the medial thigh that is relieved by flexing the hip and exacerbated by extension, adduction, and medial rotation of the hip. The Hannington-Kiff sign is an absent adductor reflex in the thigh. This is elicited by placing a finger on the adductors 5 cm above the knee, then percussing said finger with a tendon hammer. A contraction of muscle indicated an adductor reflex that is present. The Hannington-Kiff sign is more specific than the Howship-Romberg sign, but could be hard to elicit, and is operator dependent.[13]

Evaluation

It is important to note that the physical signs of an obturator hernia are operator dependent and may not be immediately evident. In these cases, it would be prudent to perform computed tomography (CT) scan to achieve an adequate diagnosis, with a reported diagnostic accuracy of up to 90%.[14]

The patient would also require general labs to be worked up for a possible operative procedure as per local protocol.

Treatment / Management

Invariably, treatment is required of these hernias due to the likelihood of there being strangulation of the hernia. Also, these hernias often require treatment as an emergency procedure, as it is unlikely that the obturator hernia is likely to be reducible. 

The treatment options for an obturator hernia are thus to be decided between an open and laparoscopic procedure. Laparoscopic hernia repairs are becoming more prevalent, with a number of reports of obturator hernia being repaired via a minimally-invasive approach [7],[15],[16]. Given the location of this hernia deep within the pelvis, a laparoscopic approach allows for clear visualisation of the contents of the hernia and subsequent treatment. Almost all case reports published have described a transabdominal preperitoneal (TAPP) approach.[15][16][17][18] This would allow the surgeon to visually inspect the contents of the hernia, and if bowel were present, to assess the viability of the incacerated/strangulated bowel. If a bowel resection were required, this could be performed either laparoscopically or via conversion to an open operation, depending on the experience of the operating surgeon.(B2)

The operative steps in an open procedure remain the same for any strangulated hernia repair – requiring a lower midline laparotomy, identification of the hernia, inspection of the contents, with possible bowel resection and anastomosis, followed by repair of the hernial orifice with either primary suture repair or with mesh placement [19]. Other approaches are described, including retropubic and inguinal approaches; however, these should be performed by surgeons with experience in such approaches.[20] A lower midline laparotomy being a very common approach may be one that surgeons would be more familiar with, and less likely to cause any issues.

The laparoscopic approach has been described previously. For a TAPP repair, pneumoperitoneum is achieved (normally via an open Hassen technique), with ports placed 5cm either side of the midline below the umbilicus. This is especially so as it would be prudent for the clinical evaluation of the contralateral side (if initially diagnosed with a unilateral obturator hernia), as there might be missed bilateral herniae in this population.[21] Once the hernial sac is identified, it is gently retracted using careful dissection if required. The hernial contents are visualized, paying attention to the bowel if present. A bowel resection may be required and will follow well-established operative steps. The excess hernial sac may be left behind, avoiding unnecessary dissection. The final part of the procedure would be the placement of a mesh. An incision is made on the anterior aspect of the abdomen using diathermy. This incision is then extended using sharp dissection, thus allowing the surgeon to tease the peritoneum alone away from the pre-peritoneal fat. Once adequate space is created, a mesh may be placed in this space. The peritoneal covering is then sutured closed.

Differential Diagnosis

It is important to note that an obturator hernia is still a rare hernia. In the presence of absolute constipation in an elderly patient, it becomes important to try and elicit whether this could be a small or large bowel obstruction. Small bowel obstruction in this population is commonly due to hernias, adhesions, and tumors, whereas large bowel adhesions are likely due to tumors, hernia, and volvulus. The diagnosis will require a form of cross sectional imaging, commonly a CT scan, after ensuring the patient is appropriately resuscitated.

Prognosis

Obturator herniae pose an interesting challenge in estimating mortality - due to their rare presentation. Historically, the mortality has been estimated between 13% to 40% and has been reported in more recent reports as well.[22][23][24] Equally, the morbidity of the condition relates to the late presentation and identification of the problem. This can lead to infective complications (such as the development of collections) and anastomotic leaks (due to bowel resections).[25]

Complications

The complications from an obturator hernia follow any other hernia, including strangulation (leading to bowel resection and associated complications), damage to the obturator nerve due to compressive symptoms, along with associated operative complications.