Spigelian hernia (SpH) is a rare form of ventral hernia, mostly acquired. It is named after the Flemish anatomist Adriaan van den Spieghel (1578-1625), who introduced several anatomical descriptions. Notably, he described the Linea semilunaris, originally called Linea semilunaris spigelii [1]. However, the first mention of SpH itself was a century later by the Bohemian anatomist and surgeon Josef Klinkosch. He described a ventral hernia occurring in the area of the Linea spigeli, hence called Spigelian hernia [2].
The incidence of SpH is currently unknown, but the number of reported cases has increased recently with the growing use of imaging techniques. Due to its specific anatomical location under the external oblique aponeurosis, SpH remains a diagnostic challenge. Additionally, SpH has a significantly higher risk of incarceration compared to other abdominal wall hernias. Therefore, even asymptomatic SpH should be considered for elective repair. Nowadays, SpH, like other ventral hernias, can be treated with minimally invasive techniques, even in emergency situations. However, there are no clear guidelines preferring one laparoscopic technique over another, although morbidity and recurrence rates are generally low and based on several patient series. For large hernias or emergency surgeries with expected bowel resection, the open approach remains a valid option. Aside from some anatomical limitations of the TEP approach, none of the existing minimally invasive approaches has proven superior. Intra-abdominal laparoscopic procedures are easier to learn and perform and offer a better overview of the abdominal cavity. Regardless of the technique used, mesh repair is recommended. However, for small hernias, repair without mesh is also a viable alternative.
Surgically Relevant Anatomy
SpH is defined as the protrusion of local preperitoneal fat tissue or a hernia sac through a defect in the Spigelian aponeurosis. The Spigelian aponeurosis is the fascia of the transversus abdominis muscle, laterally bounded by the Linea semilunaris (extending from the 9th rib to the symphysis) and medially by the lateral edge of the rectus muscle. SpH is an interstitial herniation with penetration of the aponeurosis of the transversus abdominis and the internal oblique muscle, while the superficial fascia of the external oblique muscle usually remains intact. The predilection site of SpH is the intersection between the Linea semilunaris and the Linea arcuata.
In a recent series, Spigelian hernias cranial to the Linea arcuata were reported in more than 10% of affected patients [5]. The term "low Spigelian hernia" refers to a subtype of SpH located caudal to the inferior epigastric artery within Hesselbach's triangle, first introduced by Spangen [4] and found in the series by Klimopoulos [6] in about 8% of surgically treated inguinal hernias.
In the axial plane, the hernia sac tends to extend laterally into the interstitial layer between the internal and external oblique muscles without penetrating the intact external oblique aponeurosis. This observation was confirmed in a French series of 51 patients in 90% of SpH cases [7]. The specific anatomical situation of SpH, with a rather small hernia orifice, usually not exceeding a diameter of 2 cm, and the development of an interoblique hernia sac complicate the diagnosis of this condition with a particular tendency towards incarceration.
Epidemiology
The actual incidence of SpH in the general population remains unknown, as many patients never develop symptoms leading to a diagnosis. Previous reports suggest an incidence of 1-2% of all ventral hernias [5, 8]. In a large ultrasound study of 785 anterior abdominal wall hernias, 1.4% were diagnosed as SpH [9]. In a recent study where over 200 patients were laparoscopically screened for occult ventral hernias, a defect in the Spigelian fascia was found in 2% of asymptomatic patients [8]. According to the largest published series, SpH primarily affects the adult population, with an average age of 65 years at diagnosis [5, 10]. SpH occurs more frequently in women, with a female-to-male ratio of 2:1 [5, 11, 12]. Previous pregnancies and increased intra-abdominal pressure during childbirth are considered predisposing factors [13, 14].
A "natural progression" of SpH in adults was recently supported by the observation that younger patients mostly have smaller Spigelian fascia defects with only preperitoneal content, in contrast to older patients who tend to show larger hernias with peritoneal content at diagnosis [5]. According to a systematic review encompassing more than 200 SpH cases, SpH appears to slightly predominate on the left side for unknown reasons [15].
The most important epidemiological feature is the risk of incarceration requiring emergency intervention, affecting up to 24% of all SpH cases, confirmed by current data at 17% [4, 5, 10]. This is mainly due to the small and narrow defect in the Spigelian fascia compared to the hernia content [5, 10, 16]. Compared to other ventral hernias, SpH has a significantly increased risk of incarceration. For example, umbilical hernias report a 5-year incarceration risk of only 4% during the observation period [17]. For inguinal hernias, the risk varies between 0.27 and 2.5% depending on the follow-up period [18].
Clinical Presentation
Patients most commonly suffer from intermittent pain and swelling in the lower abdomen [15]. According to Larson et al [10], two-thirds of patients describe clinical symptoms without clinical findings. Webber et al. suggest that SpH develops in two stages: first, a small SpH without a peritoneal component, typically occurring in younger patients who only complain of intermittent pain without a palpable hernia sac; and second, a larger SpH with a palpable hernia sac [5]. The most commonly incarcerated structures are the small intestine, greater omentum, and sigmoid colon [5]. Several case reports have described incarceration of unusual hernia contents such as Meckel's diverticulum, stomach, ovary, or bladder [39-41].
A "low Spigelian hernia" can be mistaken for an inguinal hernia, and the definitive diagnosis is often made intraoperatively [5, 6]. The coexistence of a "low Spigelian hernia" with a direct inguinal hernia has been described, most likely due to an accompanying weakness of the Spigelian fascia at the insertion of the rectus abdominis [19].
Differential diagnoses of a palpable hernia sac in the typical SpH region include lipomas [5], rectus abdominis hematomas, or solid abdominal tumors. Pain in the left inguinal region without a palpable hernia sac can be confused with all other causes of left-sided abdominal pain, such as acute sigmoid diverticulitis [20].
Classification
SpH is classified among primary ventral hernias, for which the European Hernia Society (EHS) classification can be applied [21]. The EHS classifies primary abdominal wall hernias solely by defect diameter:
- small < 2 cm (most common defect size in SpH)
- medium ≥ 2-4 cm
- large > 4 cm
Recently, a distinction between SpH with and without a peritoneal component was described, affecting the choice of appropriate surgical approach [5]. "Low Spigelian hernias" can be classified into the inguinal hernia classification according to Nyhus (Type Ib) or Gilbert (Type 5) [6].
Predisposing Factors
As with other ventral hernias, patients with SpH regularly exhibit factors contributing to increased intra-abdominal pressure, such as COPD, chronic cough, and obesity. Slakey et al. hypothesized that pneumoperitoneum during a laparoscopic procedure could contribute to the development of SpH through a pre-existing weakness of the Spigelian fascia, describing a case of incarcerated Spigelian hernia following a laparoscopic living donor nephrectomy [22]. SpH is often diagnosed in patients who simultaneously suffer from another ventral hernia, either currently or in the past [15, 23]. Continuous ambulatory peritoneal dialysis has also been described as a risk factor [11, 24].
Diagnostics
SpH remains a clinical diagnosis, which can be challenging. Imaging techniques such as abdominal wall ultrasound or computed tomography are usually performed in cases of doubtful diagnosis. In the largest published series to date, the diagnosis could be confirmed by imaging in up to 20% of cases with unclear physical examination [10]. Several studies indicate that abdominal sonography is a meaningful imaging technique for SpH with a sensitivity of 83-90% [24-26]. The advantage of CT imaging lies in the ability to identify the hernia content in addition to depicting the hernia defect. For occult SpH, imaging diagnostic confirmation is recommended [25]. Diagnostic laparoscopy is reserved for patients with persistent symptoms and unclear ultrasound and CT findings [27, 28].
Treatment Options
The most commonly described early complications are seromas, hematomas, and wound infections. Postoperative complications are generally rare [15, 29]. Skouras et al. reported 2.3% postoperative complications after laparoscopic procedures [30], compared to 18% in open surgeries [11]. However, both studies reported rather small cohorts, and only six patients represented the relatively high complication rate in open surgeries.
Due to the significant risk of incarceration, all SpH should be surgically treated [5, 10, 29]. According to the latest EHS guidelines, there are no definitive recommendations for open or minimally invasive procedures; the choice of procedure is at the surgeon's discretion [28]. The recurrence rate is generally very low, especially after mesh placement [23, 30]. As with all ventral hernias, a mesh overlap of more than 5 cm over the defect is mandatory. The closure of the SpH defect before mesh placement is controversial and is not explicitly commented on in the EHS position 2020 [28, 31]. In most mesh repairs, regardless of the technique used, a polypropylene mesh can be used, except for intra-abdominal mesh placement, where a composite mesh should be used for adhesion prophylaxis [23, 31, 34].
Open vs. Laparoscopic
The first laparoscopic surgery for SpH was performed in 1992 [32]. Minimally invasive techniques also lead to lower postoperative morbidity in the treatment of SpH, shorten hospital stays, and allow for an earlier return to normal activities [11, 23]. The intraperitoneal laparoscopic approach has the advantage of easier examination of the entire abdominal wall, while open standard repair may require a longer incision, especially if the SpH is not palpable [31].
Despite the development of minimally invasive techniques, there are still some advantages to open surgery. Relative to the size of the SpH, a small preperitoneal SpH without a peritoneal sac and content can be difficult to detect laparoscopically. On the other hand, a voluminous SpH, where extensive abdominal wall repair is expected, is probably best treated with an open approach [5]. Additionally, treatment under regional anesthesia is only possible with open repair [11]. Anterior hernioplasty with preperitoneal sublay mesh under local anesthesia has been described as a successful outpatient procedure without long-term recurrences [33].
Laparoscopic Procedures
Similar to the treatment of other ventral or inguinal hernias, minimally invasive techniques IPOM (IntraPeritoneal Onlay Mesh), TEP (Totally ExtraPeritoneal), and TAPP (TransAbdominal PrePeritoneal) can also be used in SpH repair. Currently, there is no solid recommendation for any of these methods, but some advantages and possible limitations have been described. The only existing prospective study comparing TEP with IPOM repair showed excellent results for both methods without complications or recurrences after 4 years [31]. However, it is reported that the TEP method incurs twice the overall cost compared to IPOM, mainly due to the price of the balloon dissector.
The TEP repair is preferred by some authors because it does not require access to the abdominal cavity and reduces the risk of intra-abdominal adhesions [27]. Moreno-Egea et al. suggest the TEP repair for patients with "low Spigelian hernia" and relatively small size [31]. Additionally, the TEP approach can only be applied if the SpH is located below the arcuate line [5]. A possible advantage of the TEP repair is the ability to detect and address an accompanying direct inguinal hernia [19].
The advantage of the IPOM procedure and also the TAPP method is the ability to explore the entire abdomen [23, 30, 34]. Both methods have also been described in emergency situations with incarcerated hernia content. The IPOM method is considered the easiest to learn and safest to perform [31].
The biggest limitation of IPOM is the risk of nerve injuries or hematomas due to the use of staples or tacks. A possible solution proposed is fibrin sealing instead of staples [35]. However, there are no published data on IPOM in SpH describing complications from staples or intraperitoneal meshes [31]. According to Moreno-Egea et al., a SpH size > 3 cm, bilateral hernia, and non-reducible content favor an intraperitoneal technique.
A possible limitation of the TAPP method, pointed out by Moreno-Egea et al. [31], is the potential difficulty in closing the peritoneal flap due to the thinner and more fragile peritoneum at this site.
The laparoscopic, totally extraperitoneal single-incision repair (SIL-TEP) of SpH has been introduced as an alternative technical approach. The main advantage highlighted was cost savings through telescopic extraperitoneal dissection instead of the standard balloon dissector used in the TEP technique. The authors reported no recurrence after a short follow-up period of 9 months [19].
Recently, case reports on robot-assisted SpH repair with promising preliminary data have been published [36, 37].
There is relatively little literature specifically addressing emergency surgery for SpH. SpH emergencies have been described in case reports. In the series by Larson et al., describing eight patients with clinical emergencies, seven patients had incarcerated tissue that had to be resected [10].