Retroperitoneal hernias are exceedingly rare, posterolateral, parietal wall defect in the lumbar region containing retroperitoneal fat or viscera [10]. Retroperitoneal hernia are included in the group of lumbar hernias, with less than 400 cases reported in the literature and account for 2% of all abdominal wall hernias [11, 12].

They can be classified anatomically into superior or inferior lumbar hernias based on two well-defined areas of weakness. The superior lumbar triangle, describe by Grynfetl in 1886 [13], and the inferior lumbar triangle or Petit triangle, first described in 1783 [14, 15]. Herniation occurs more commonly in the superior triangle as it has a greater surface area compared to the inferior triangle, the reason why Grynfelt-Lesshaft hernias are much more common than Petit hernias [16].

In addition to the anatomic classification, lumbar hernias can further be categorized as congenital and acquired, which make up 20% and 80% of lumbar hernias, respectively [17]. On the one hand, congenital lumbar hernias are usually diagnosed during the pediatric age, and are most often associated with other congenital anomalies such as the lumbocostovertebral syndrome [18,19], although it has been reported with neural tube defects such as spina bifida [20]. On the other hand, acquired lumbar hernias can be primary or secondary [17]. Primary acquired lumbar hernias are more common, comprising 55% of all lumbar hernias [17]. Risk factors for developing a primary hernia are obesity, connective tissue disease, poor nutritional status, and conditions that increase intra-abdominal pressure, as the persistent cough [21]. Secondary lumbar hernias are either iatrogenic, traumatic, or following recurrent infection or inflammation process [22], and account for 25% of acquired lumbar hernias [13].

Lumbar hernias can lead to intestinal obstruction and intestinal strangulation after delayed diagnosis due to atypical clinical symptoms. Although strangulation of abdominal contents through a lumbar hernia is a very rare condition, with no more than 30 cases reported in the literature [23], the failure to resolve the obstructed circulation can be life-threatening because of intestinal necrosis.

Although post-traumatic lumbar wall herniations are relatively rare injuries, they should be suspected in patients with high-energy torso injuries [24]. In this sense, the only case of retroperitoneal hernia secondary to a lumbar vertebral fracture was described by Huang et al. in a patient who had suffered a traffic accident [25].

Most of the iatrogenic retroperitoneal hernias described in the literature have been related to injury to the retroperitoneal fascia in renal transplant surgery [26], retroperitoneal nephrectomies [27], radical cystectomy [28], or obtaining bone graft from the iliac crest [29], among others. However, hardly any cases of retroperitoneal hernias have been reported in the context of spinal surgery, and most of them are incisional hernias associated with lateral approaches to the thoracolumbar spine [9], whose usual clinical presentation is a bulging mass at the their lateral incision site. Although some authors suggest that its true incidence may be underestimated [30], only twenty three cases of incisional hernias have been described as a consequence of a lateral approach to the spine [30–35]. Most patients complained of a bulging mass at their lateral incision site. Furthermore, it should be noted the work published by Colosimo et at., in which to date is the only reported case of a patient with recurrent small bowel obstruction caused by a symptomatic retroperitoneal hernia secondary to anterior retroperitoneal lumbar spinal exposure [7].

In the surgical anatomy of the abdominal retroperitoneal spaces, the thoracolumbar fascia separate the paraspinal muscles from the muscles of the posterior abdominal wall and its middle layer is attached to the tips of the transverse processes of the lumbar vertebrae and extends laterally behind the quadratus lumborum [36], while the transversalis fascia forms the outer stratum of the retroperitoneal fascia, which lies deep to the transversus abdominis muscle and superficial to the preperitoneal fat and peritoneum [37]. Besides, some texts include the fascia of the psoas muscle with the transversalis fascia [38].

Therefore, and apart from the lateral approach surgery, which is fundamentally a retroperitoneal approach where there is a potential risk to damage intra- and retroperitoneal structures due to a close relationship between the surgical approach and the retroperitoneal fascia, in posterolateral fusion techniques in which a decortication of the transverse processes of the lumbar vertebrae is performed, there may be a risk of damaging the thoracolumbar and transversalis fasciae at the time of their dissection and surgical exposure, especially in those patients with paravertebral muscle atrophy and fatty degeneration. In fact, and similarly to our case, posterolateral fusion has been demonstrated as the most invasive procedure of the paraspinal muscles whose damage during lumbar back surgery may be one of the most important factors that causes atrophy of the muscles [39].