Abstract
BACKGROUND
Lateral lumbar interbody fusion (LLIF) is a minimally invasive spinal fusion technique utilizing a lateral transpsoas approach to access the anterior column of the spine. Vascular injury is a rare complication but difficult to manage due to the minimally invasive nature of the procedure, making it critical to carefully review preoperative imaging prior to committing to a lateral approach.
OBSERVATIONS
A 67-year-old female presented with progressive low back pain and left lower extremity pain and sensory changes. MRI showed a grade 1 L4–5 spondylolisthesis with left-sided neuroforaminal stenosis. The patient was recommended for LLIF; however, on further review of the MRI findings, an abnormally dilated left gonadal vein (GV) was identified along the psoas muscle. Subsequent imaging revealed compression of the left renal vein between the superior mesenteric artery and aorta, causing venous outflow obstruction. Therefore, the surgical approach was changed to avoid potential vascular complications.
LESSONS
GV injury is a rare but major complication of lateral spine surgery. This case highlights the importance of careful preoperative imaging and anatomical review as lateral approaches become more common, and acts as a cautionary report for vascular review prior to LLIF.
Keywords: lateral lumbar interbody fusion, LLIF, minimally invasive spinal fusion, gonadal vein
ABBREVIATIONS: GV = gonadal vein, IVC = inferior vena cava, LLIF = lateral lumbar interbody fusion, OLIF = oblique lumbar interbody fusion, RV = renal vein, SMA = superior mesenteric artery, TLIF = transforaminal lumbar interbody fusion
Lateral lumbar interbody fusion (LLIF) is a minimally invasive spinal fusion technique that utilizes a lateral flank incision to access the anterior column of the spine. LLIF is suitable for pathology impacting the thoracolumbar junction to the L4–5 space, but is not suitable for the L5–S1 level due to obstruction by the iliac crest, increased risk of neural injury due to a more anterior course of the lumbar plexus, and increased risk of vascular injury due to a more lateral position of the iliac vessels.1 LLIF has gained popularity due to the potential reduction in surgical morbidity associated with avoiding the great vessels and abdominal organs during the anterior approach, as well as avoiding direct manipulation of the thecal sac and nerve roots required in posterior approaches.2,3 Therefore, LLIF allows for larger interbody cage insertion than posterior approaches in order to maximize sagittal and coronal deformity correction and increase cage-endplate contact space to allow for fusion.1,2,4
The surgical technique includes blunt dissection in the retroperitoneal space to reach the psoas muscle, which is then entered with a dilator to access the lateral disc space. This is typically carefully performed under direct neuromonitoring to ensure there is no damage to the lumbar plexus, which runs along the posterior aspect of the psoas muscle. Complications associated with the LLIF include, but are not limited to, injury to the lumbar plexus resulting in transient versus permanent weakness and sensory changes, pain associated with psoas dissection, vascular and visceral abdominal organ injury, and device-related malfunction.5,6
Vascular injury in LLIF is rare, but due to the minimally invasive nature of the procedure, it can be challenging to control, which makes it critical for a surgeon to carefully review preoperative imaging prior to committing to a lateral approach.7 We present an atypical case of a patient with degenerative disease at L4–5 who was found to have a dilated gonadal vein (GV) running along the ventrolateral psoas identified on preoperative imaging, leading to a change in the planned surgical approach from LLIF to transforaminal lumbar interbody fusion (TLIF) and avoidance of a potential vascular injury.
Illustrative Case
A 67-year-old female with a history of hypertension, migraines, depression, and prior left L4–5 hemilaminotomy performed 3 years earlier for left leg pain presented with 1–2 years of progressive low back pain, left hip region pain and numbness, and numbness along the left ankle and foot. She underwent physical therapy for 6 weeks and had an epidural injection with minimal relief. On physical examination, she had normal gait, muscle mass, and tone. She had full strength in the bilateral lower extremities. She reported numbness of the left foot and ankle with otherwise intact sensation to light touch. MRI and radiographic imaging of the lumbar spine showed a grade 1 L4–5 spondylolisthesis with resultant left-sided neuroforaminal stenosis and impingement of the exiting L4 nerve root (Fig. 1).
FIG. 1.
Preoperative T2-weighted sagittal (A) and axial (B) MR images of the lumbar spine. Lateral (C) and anteroposterior (D) radiographic images of the lumbar spine demonstrating L4–5 spondylolisthesis and stenosis.
The patient was recommended a fusion surgery with an initial plan for LLIF. During further preoperative MRI review by the treating neurosurgeon, a questionable structure along the ventrolateral psoas muscle was identified and, with input from a vascular surgeon, recognized as an abnormally dilated GV (Fig. 2). Therefore, further preoperative imaging was obtained with CT angiography of the abdomen/pelvis, which revealed compression of the left renal vein (RV) between the superior mesenteric artery (SMA) and aorta, resulting in a severely dilated left GV in the setting of left RV entrapment, causing venous outflow obstruction, commonly known as the nutcracker phenomenon (Figs. 3– 5). In light of this finding, along with a less pronounced but still dilated right-sided GV, the patient was counseled regarding the implications and the surgical approach was changed to L4–5 TLIF to avoid potential vascular complications related to the vessel’s proximity to the planned transpsoas working corridor at L4–5.8
FIG. 4.
Preoperative 3D reconstruction CT angiogram of the abdomen/pelvis demonstrating a dilated GV (arrow).
FIG. 2.
Preoperative T2-weighted axial MR image of the lumbar spine demonstrating a dilated vascular structure (arrow) consistent with the left GV at the ventrolateral aspect of the psoas muscle.
FIG. 3.
Preoperative axial (A), coronal (B), and sagittal (C) CT angiograms of the abdomen/pelvis demonstrating a dilated left GV (LGV) at the level of spondylolisthesis (line).
FIG. 5.
Preoperative sagittal CT angiogram of the abdomen/pelvis demonstrating a compressed left RV (LRV) between the SMA and aorta.
The patient underwent an uneventful minimally invasive L4–5 TLIF. She did well postoperatively, worked with physical therapy, and was discharged home on postoperative day 4. At the 2-week follow-up, she noted some surgical pain but minimal preoperative left lower extremity pain. At the 6-week follow-up, she had some left lower extremity discomfort, but her pain was significantly improved compared to preoperatively. Radiographic imaging of the lumbar spine at the 6-week follow-up demonstrated satisfactory hardware placement without complication.
Informed Consent
The necessary informed consent was obtained in this study.
Discussion
Observations
LLIF has been shown to be a reliable option for minimally invasive spinal fusion with an acceptable risk profile; however, this case highlights a potential pitfall due to aberrant dilation of vasculature in proximity to the surgical corridor secondary to a rare anatomical variant.
The GVs are paired vessels that drain venous blood from the testes in males and the ovaries in females. The right GV typically terminates directly into the inferior vena cava (IVC) at an acute angle, whereas the left GV most commonly drains into the left RV before joining the IVC, often at a perpendicular orientation that predisposes to elevated hydrostatic pressure. Variations in drainage patterns and vessel number are well documented.9 Anatomical studies have demonstrated that numeric and drainage variations, such as duplication or anomalous drainage of the GVs, occur and have clinical relevance for conditions like varicocele and pelvic congestion syndrome as well as intraoperative planning and retroperitoneal surgery.10 The left GV is vulnerable to elevated venous pressures in instances of left RV hypertension when the left RV is compressed anteriorly between the SMA and the aorta, a condition known as the nutcracker phenomenon, which can lead to secondary dilation of the GV and the clinical nutcracker syndrome of pelvic venous congestion. Common GV anatomical variations include accessory or duplicate GVs, direct drainage of a GV into the RV or IVC in atypical patterns, and variability in vessel course and caliber, all of which can influence surgical approaches. Management of symptomatic left RV compression and associated GV hypertension ranges from conservative observation to surgical or endovascular interventions, including left RV transposition, selective left RV stent placement, and autotransplantation of the left kidney.11
The nutcracker phenomenon yields downstream venous congestion, including to the GV, but this relationship has not been analyzed in the setting of spine surgery. As lateral approaches to the anterior column of the spine become increasingly utilized, this relationship is critical for surgeons to understand to prevent vascular injury.
In the setting of LLIF, the GV is an important anatomical consideration due to its potential for major bleeding if injured, but given its typical smaller size and anterior position, it is an underreported source of vascular injury due to the rare incidence of injury. A study by Kagami et al. aimed to investigate the anatomical position of the GV in the lumbar spine and its associated risk factors in LLIF.12 They divided GV locations into three distinct regions: ventral to the vertebral body, dorsomedial between the vertebral body and the midpoint of the psoas, and dorsolateral to the midpoint of the psoas. The group noted that the dorsomedial position may be the most dangerous, as its dorsal location places it within the LLIF working corridor and in a relatively blind region medial to the psoas. They noted that at the upper lumbar levels (L1–2 and L2–3), the GVs were commonly located ventral to the vertebral body and psoas muscle but more dorsally at the lower lumbar levels (L3–4 and L4–5).12 The group also found that a dorsomedial location of the GV was associated with females and with degenerative scoliosis and spinal sagittal malalignment.12 In our case, the left GV was located in proximity to the anticipated transpsoas working corridor at L4–5 and would not have been directly visualized until after retractor deployment, at which point it may have already been at risk during dilator and retractor placement.
Regarding reports of injury to the GV, Zeng et al. analyzed complications associated with oblique lumbar interbody fusion (OLIF) and reported 4 major vascular injuries with only 1 injury being to the GV (0.43%).13 Aguirre et al. reported a case series of 260 patients who underwent either LLIF (211 patients) and OLIF (49 patients), analyzing major and minor vascular injuries, and identified no injuries to the GV in their patient population.14 The group also performed an in-depth literature review of major vascular injury in lateral interbody surgery and did not identify a report of GV injury aside from that in the Zeng study.13,14
Lessons
Although rare, GV injury is a major complication of lateral spine surgery associated with difficult to control hemorrhage and morbidity.1,7 The presence and identification of the GV is critical in all lateral approach spine cases, but especially in the setting of the nutcracker phenomenon. As lateral approaches become more common, it is critical that spine surgeons continue to familiarize themselves with nontraditional spinal anatomy and relevant pathologies in order to provide safe and effective care for their patients. This case highlights the importance of careful preoperative imaging review and acts as a cautionary report for vascular review prior to LLIF.
Acknowledgments
We acknowledge and thank the Florence D. and Irving J. Sherman MD Charitable Foundation Trust for their support for this publication.
Disclosures
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
Author Contributions
Conception and design: Hughes, Chang. Acquisition of data: Hughes. Analysis and interpretation of data: all authors. Drafting the article: Hughes, White. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Hughes. Study supervision: Chang.
Correspondence
Liam P. Hughes: Johns Hopkins University School of Medicine, Baltimore, MD. lhughe22@jh.edu.
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