Advanced spinal surgeries, such as total en bloc spondylectomy (TES) and lateral lumbar interbody fusion (LLIF), have been increasingly performed in recent years [1–3]. These procedures require dissection of the anterior and lateral tissues of the vertebral bodies through a restricted surgical field, increasing the risk of injury to the aorta, inferior vena cava, and segmental arteries and veins [4–7]. Segmental artery and vein injuries occur more often than aortic injuries and can sometimes result in hemorrhagic shock, posing a life-threatening risk [8].

TES, in particular, carries a high risk of segmental vessel injury because it involves resection of the entire vertebral body with a wide margin to treat malignant spinal tumors [9,10]. Detaching the segmental arteries and veins from the vertebral bodies is a critical step, underscoring the importance of detailed anatomical knowledge to ensure intraoperative safety. The lumbar segmental arteries typically arise from the abdominal aorta at the L1–L4 levels and course along the lateral surface of the vertebral bodies [11–13]. The corresponding veins follow a similar trajectory, draining into the ascending lumbar vein or inferior vena cava [13].

Murakami et al. [14] identified the upper lumbar spine, particularly the L2 level, as a high-risk site for segmental vessel injury during TES. At this level, the diaphragmatic crus overlies the anterior surface of the vertebral bodies [15,16], potentially obstructing vessel detachment and increasing the risk of vascular injury. To address this, they recommended dissecting the bilateral crura via an anterior approach, ligating the segmental vessels, and then resecting the tumor via the posterior approach [14,17]. However, they did not specify the indications for selecting the anterior approach. Moreover, reports of segmental artery injury during LLIF at the L2 level suggest a comparable risk of vascular injury associated with the presence of the diaphragmatic crus [18,19].

Therefore, in-depth characterization of the anatomy of segmental vessels, particularly at upper lumbar levels, is vital for preventing vascular injury. Prior anatomical studies have reported considerable variations in segmental artery pathways. For example, Nojiri et al. [20] described arteries traversing laterally, across the intervertebral discs, whereas Yagi et al. [19] reported an anomalous course running anteriorly across the discs at higher lumbar levels. These observations highlight the complexity and variability of segmental artery anatomy, especially in the upper lumbar region.

The diaphragmatic crus may contribute to this anatomical complexity, yet no study has specifically examined its relationship with the segmental vessels. Therefore, this study aimed to investigate the anatomical relationship between the diaphragmatic crus and the lumbar segmental arteries and veins using cadaveric specimens, aiming to help reduce the risk of vascular injury during spinal surgery.

TES and LLIF are increasingly performed but demand advanced surgical expertise. In particular, lumbar spine surgeries carry a risk of segmental vessel injury, which may result in hemorrhagic shock. For example, two cases of segmental artery injury were reported among 307 TES procedures [6], and Peiro-Garcia et al. [8] described a segmental artery injury during LLIF that led to hemorrhagic shock. Such serious complications can adversely affect patient outcomes. Suzuki et al. [21] identified segmental vessel anomalies and improper device use as contributing factors. Anatomical variations are especially important: Nojiri et al. [20] described segmental arteries running vertically over intervertebral discs along the lateral aspect of the vertebral bodies, while Yagi et al. [19] reported that, in the upper lumbar spine, these arteries traverse anteriorly across intervertebral discs. These findings highlight the importance of recognizing anatomical variability to minimize the risk of vascular injury. The presence of the diaphragmatic crus in the upper lumbar spine further complicates these anatomical relationships and heightens the risk of segmental vessel injury.

Our study demonstrated variability in the origin of the diaphragmatic crus. The right crus originated more caudally than the left, with origins ranging from the L1/2 to the L3/4 intervertebral discs (Table 1). The right crus was also broader (Table 2) and located more medially relative to the vertebral midline compared with the left crus (Table 3). These anatomical differences between the left and right crura highlight the importance of considering laterality when approaching the spine from either side. Accordingly, preoperative imaging to delineate the origin and course of the crus is critical for minimizing the risk of vascular injury. At present, however, no standardized method exists for assessing the crus preoperatively.

When performing TES at the L2 level, the diaphragmatic crus can obstruct dissection of the segmental vessels from the vertebral body via a posterior approach [17]. Murakami et al. [14] reported that this issue can be addressed by detaching the crus in advance using an anterior approach. Our findings help clarify the rationale behind this recommendation. At vertebral levels cranial to the origin of the crus, the segmental arteries consistently passed between the crus and the vertebral bodies on both sides. Segmental veins, however, demonstrated asymmetry: on the right side, they coursed along the ventral surface of the crus, whereas on the left, they ran between the crus and the vertebral bodies (Figs. 3, 4). These observations suggest that whether TES is performed at L1, L2, or L3, all located cranially to the crus origin, an anterior approach to detach the crus is advisable. When dissecting the crus, it is important to consider both the width differences between the left and right sides and the anatomical variations in the relationships between segmental arteries and veins and the crus. On the right, the segmental veins lie ventral to the crus, while the arteries course between the crus and vertebral bodies. On the left, both segmental arteries and veins pass between the crus and the vertebral bodies.

Based on our findings, a left-sided anterior-posterior approach is recommended for TES performed cranial to the origin of the crus. This approach involves detaching the left crus and ligating the left segmental vessels, followed by anterior retraction of the aorta to expose the right crus. Because the right crus is broad and close to the midline, it can be partially dissected and transected with forceps. A subsequent posterior approach allows retraction of the loosened right crus and transection of the right segmental artery. In contrast, a right-sided approach, which may be selected for tumors with extravertebral extension, poses greater difficulty. The left crus is narrower and located farther from the midline, making transection from the right side more challenging. In such cases, an anterior approach from both sides is required. These side-specific anatomical relationships highlight the importance of preoperative imaging for planning a safe and effective surgical strategy.

Preoperative imaging evaluation is critical for preventing segmental vessel injury, and contrast-enhanced computed tomography (CT) has been shown to be effective for evaluating segmental arteries [22–24]. However, visualization of the crus and segmental veins remains challenging, as their courses have not been validated using CT or magnetic resonance imaging (MRI) studies. This difficulty arises because segmental veins, particularly the ascending lumbar veins, are narrow, flattened, and highly variable in course and branching pattern [25,26]. Yagi et al. [19] also noted the difficulty of accurately identifying segmental veins on contrast-enhanced CT, while Kiyohara et al. [27] reported challenges in distinguishing segmental arteries from veins in MRI. Clear visualization of the crus and segmental vessels on preoperative imaging would enable individualized surgical planning and improve procedural safety, but this remains technically difficult and warrants further research. A limitation of this study is the small number of male specimens; however, the anatomical relationship between the diaphragmatic crura and the segmental vessels is unlikely to differ significantly by sex.

In summary, this study demonstrated anatomical variations in the origin of the diaphragmatic crus, with the right crus being broader and positioned closer to the vertebral midline than the left. Segmental arteries were found to course between the crus and the vertebral bodies, whereas segmental veins followed asymmetric paths, running ventral to the crus on the right and between the crus and vertebral bodies on the left. These findings provide valuable anatomical insights for TES and LLIF and may contribute to improved intraoperative safety. Meticulous preoperative evaluation of the crus origin and segmental vessel pathways is essential to minimize the risk of vascular injury. Incorporating these anatomical details into surgical planning may enhance surgical precision and support the development of patient-specific approaches, ultimately contributing to safer lumbar spine surgery.

The diaphragmatic crus exhibits variations in its origin, width, and position relative to the vertebral midline. Together with the anatomical pathways of segmental arteries and veins, these features are critical considerations for minimizing vascular injury during lumbar spinal surgery. Meticulous preoperative evaluation of the crus and segmental vessels is therefore essential to optimize surgical planning and enhance patient safety.