Abstract
BACKGROUND
Patients with pectus excavatum occasionally develop hypotension after prone positioning during scoliosis surgery, which may result in cancellation of the surgery. The imaging characteristics associated with severe hypotension in patients with pectus excavatum remain unclear. The authors compared the cases of 3 scoliosis patients with pectus excavatum who developed hypotension after prone positioning, focusing on the spatial relationship between the great vessels and the thoracic cage on CT.
OBSERVATIONS
In only 1 of the 3 patients was the hypotension refractory to fluids and vasopressors. CT scans showed that the inferior vena cava (IVC) was located directly anterior to the aorta, and the great vessels were situated in the narrow space between the costal cartilage and the vertebral body; in the prone position, they might be easily crushed by the anterior chest wall. The chest wall, the great vessels, and the vertebral body formed a distinctive Y-shaped configuration, which the authors designated as the “Y sign.”
LESSONS
Hypotension after prone positioning in scoliosis patients with pectus excavatum is presumed to result from compression of the right heart and the IVC. The Y sign may represent an anatomical risk factor for refractory hypotension in the prone position and may support consideration of pectus excavatum repair before scoliosis surgery.
Keywords: pectus excavatum, scoliosis, intraoperative hypotension, prone position, Marfan syndrome
ABBREVIATIONS: IVC = inferior vena cava
Pectus excavatum is characterized by distortion of the anterior chest wall due to depression of the sternum and the costal cartilages.1 The prevalence of pectus excavatum in the general population is 0.1%,2 whereas it is seen in two-thirds of patients with Marfan syndrome.3 The prevalence among scoliosis patients remains unknown; however, when syndromic cases are considered, it may not be so rare. Abnormalities of the thoracic cage such as pectus excavatum have been, albeit rarely, associated with hypotension during scoliosis surgery performed in the prone position.4 To the best of our knowledge, in only 3 reported cases, hypotension after prone positioning was refractory to both fluid loading and vasopressor administration, ultimately necessitating cancellation of the surgery.5–7 Regrettably, severe hypotension could not have been predicted preoperatively.5–7 If the risk of such hypotension could be assessed in advance, prior corrective surgery for pectus excavatum might allow us to perform safer scoliosis surgery in the prone position.
Our prefecture has a population of approximately 2.2 million people, and two institutions manage all scoliosis cases. We retrospectively reviewed the data of 326 patients who underwent corrective surgery for syndromic or idiopathic scoliosis at these two institutions between 2014 and 2024 (49 males and 277 females; mean age 17 years). Among these patients, 6 had pectus excavatum. In 3 of the 6 patients, severe hypotension—defined as a > 30% reduction in systolic blood pressure8—was observed when they were placed in the prone position. In this report, we compared the 3 cases focusing on the severity of hypotension after prone positioning and the spatial relationship between the aorta and the inferior vena cava (IVC) within the thoracic cavity as visualized on preoperative CT scans, and discussed the anatomical factors that may contribute to the severity of hypotension leading to discontinuation of the surgery.
Illustrative Cases
We identified 3 patients with syndromic scoliosis and pectus excavatum, all of whom had Marfan syndrome. A summary of these cases is shown in Table 1. Only in case 1, after the patient was placed prone, did refractory hypotension occur, necessitating cancellation of the surgery. The preoperative axial chest CT scans revealed a narrowed space between the costal cartilages and the vertebral body (Fig. 1A). The deepest point of the chest wall depression, the IVC, the aorta, and the anterior surface of the vertebral body were aligned along a straight line, forming a distinctive pattern resembling the letter “Y” (Fig. 1B), which we designated as the “Y sign.” This sign was not detected in cases 2 and 3 (Fig. 2). In both cases, the blood pressure dropped after prone positioning, but increased promptly with fluid loading and vasopressor administration. We describe cases 1 and 2 below and show the contrasting imaging findings.
TABLE 1.
Summary of the present cases
| Case No. | Age, yrs | Marfan Syndrome | Main Curve | Surgery | Blood Pressure, mm Hg | HI | IVC Position | Y Sign | Abortion of Op | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Level | Preop | Postop | Position | Procedure | Supine | Prone | |||||||
| 1 | 14 | Yes | T6–12 | 99° | 73° | 1st: lt lat decubitus | Ant release | 97/56 | 25/17 | 5.5 | Ant to aorta | Yes | Yes |
| 2nd: prone | Pst corrective fusion | ||||||||||||
| 2 | 14 | Yes | T7–12 | 48° | 23° | Prone | Pst corrective fusion | 134/77 | 65/38 | 9.8 | Rt of aorta | No | No |
| 3 | 21 | Yes | T2–6 | 70° | 37° | Prone | Pst corrective fusion | 106/39 | 73/37 | 6.5 | Rt of aorta | No | No |
Ant = anterior; HI = Haller index; pst = posterior.
FIG. 1.
Axial plain chest CT scans showing the spatial relationship between the great vessels before and after pectus excavatum repair in case 1. A: The IVC is indicated by a solid line, and the aorta by a dotted line. The costal cartilage at the deepest point of the chest wall depression is marked with an arrow, and the vertebral body with an arrowhead. Preoperatively, the IVC was located anterior to the aorta and directly posterior to the deepest point of the chest wall. B: This alignment of the costal cartilages, great vessels, and vertebral body formed a distinctive pattern resembling the letter “Y.” C: After pectus excavatum repair, the space between the costal cartilage and the vertebral body widened, and the position of the IVC (solid line) shifted to the right of the aorta (dotted line).
FIG. 2.
Axial plain chest CT scans showing the spatial relationship between the great vessels in cases 2 and 3. The IVC is indicated by a solid line, and the aorta by a dotted line. A: In case 2, the IVC is located to the right of the aorta, which represents its anatomically normal position. B:Since case 3 had already undergone surgery for pectus excavatum, the space around the great vessels was preserved. Additionally, the IVC is located to the right of the aorta, as in case 2.
Case 1
A 14-year-old male with syndromic scoliosis due to Marfan syndrome had pectus excavatum. The Haller index, defined as the ratio of the transverse chest diameter to the anteroposterior diameter, was 5.5 (normal ≤ 2.5).9 Radiographs revealed a 99° thoracic curve with a Cobb angle from T6 to T12. Axial CT scans demonstrated that the alignment of the great vessels and the chest wall formed a Y-shaped configuration (Fig. 1B). The scoliosis surgery was planned in two stages. Anterior release from the right side at T7–10 in the left lateral decubitus position was performed first. Then 1 week later, instrumented posterior corrective fusion from T2–L3 in the prone position was planned.10 The patient’s blood pressure was 97/56 mm Hg after induction of general anesthesia and dropped to 25/17 mm Hg immediately after turning to the prone position. As hypotension did not respond to fluid loading and vasopressors, the patient was returned to the supine position 10 minutes after prone positioning. Systolic blood pressure increased immediately thereafter, but the surgery was aborted as it was difficult to maintain adequate blood pressure in the prone position. The change in intraoperative blood pressure is shown in Fig. 3. To plan the scoliosis reoperation, pectus excavatum repair surgery was performed 10 months after the initial surgery, resulting in an improvement of the Haller index to 3. Axial CT scans showed an expanded space between the costal cartilages and the vertebral body, with the IVC shifted to the right of the aorta (Fig. 1C). Before the reoperation, a prone position test was conducted in the operating room for 10 minutes and his blood pressure remained stable.11 The reoperation was performed as a two-stage procedure combining anterior release at T7–10 via a posterior approach and posterior corrective fusion from T2 to L4 and was completed.12 Postoperative radiographs showed that the main thoracic curve from T6 to T12 was corrected to 73°.
FIG. 3.
Time course and blood pressure changes. Intubation was performed at time zero in the figure. The dotted line indicates the time when the patient was placed in the prone position, and the solid line indicates the time when he was returned to the supine position. His blood pressure in the supine position was 97/56 mm Hg. After the patient was placed in the prone position, his blood pressure dropped to 25/17 mm Hg. Ten minutes after being placed in the prone position, because the hypotension did not respond to vasopressors, the patient was returned to the supine position, resulting in an immediate rise in systolic blood pressure.
Case 2
A 14-year-old female with syndromic scoliosis due to Marfan syndrome had pectus excavatum. Radiographs revealed a 48° thoracic Cobb angle from T7 to T12. The Haller index was 9.8. Axial CT scans demonstrated that the IVC was located to the right of the aorta and the deepest point of the chest wall depression (Fig. 2A). Unlike case 1, the alignment of the great vessels and the chest wall did not form a Y-shaped configuration. Instrumented posterior corrective fusion from T3 to T7 was planned in the prone position. After induction of anesthesia, the patient’s blood pressure dropped from 134/77 mm Hg to 65/38 mm Hg when she was placed in the prone position but increased with fluid loading and vasopressor administration. Postoperative radiographs showed that the main thoracic curve from T7 to T12 was corrected to 23°.
Informed Consent
The necessary informed consent was obtained in this study.
Discussion
Observations
The incidence of hypotension associated with the supine to prone positional change during spine surgery was reported to be 8.9%.4 Risk factors for such hypotension include pectus excavatum, advanced age, a history of cardiac disease, and preoperative use of beta-blockers or high-dose opioids.4 However, the risk factors for refractory hypotension requiring cancellation of surgery remain unclear.
Marfan syndrome may contribute to hypotension in the prone position, as increased thoracic cage compliance may facilitate compression of cardiovascular structures in addition to deformity of the thoracic cage.11 In fact, all 3 of the present patients had Marfan syndrome, but only 1 patient developed refractory hypotension. In addition, Marfan syndrome was absent in 2 of the 3 reported cases with marked hypotension (Table 2). These observations suggest that Marfan syndrome alone does not fully explain prone position hypotension refractory to fluids and vasopressors, and that additional factors, including anatomical factors, may contribute. The Haller index is a common indicator of the severity of pectus excavatum. A normal value is generally considered to be < 2.5, and a value ≥ 3.25 is generally regarded as severe.9 Although Marfan syndrome is associated with cardiopulmonary dysfunction,13 whether it serves as a risk factor for hypotension after prone positioning remains unclear. These 3 patients had comparable severity of pectus excavatum by the Haller index. Case 1 experienced the most severe hypotension, although he had the lowest Haller index (Table 2). Therefore, it may not necessarily be associated with the severity of hypotension in the prone position.
TABLE 2.
Summary of the previous reports
| Authors & Year | Age, yrs | Past History | Blood Pressure, mm Hg | Causes of Hypotension | HI | Position of IVC | Y Sign | Abortion of Op | |
|---|---|---|---|---|---|---|---|---|---|
| Supine | Prone | ||||||||
| Alexianu et al., 20045 | 2.8 | NF | 80 (SBP) | 20 (SBP) | Compression of rt ventricle | NA | NA | NA | Yes |
| Bafus et al., 20086 | 15 | MS-like | NA | 60 (MAP) | Compression of rt heart | NA | NA | NA | Yes |
| Galas et al., 20097 | 15 | NA | 103/61 | 60 (SBP) | Compression of rt heart | NA | NA | NA | Yes |
MAP = mean arterial pressure; MS = Marfan syndrome; NA = not available; NF = neurofibromatosis; SBP = systolic blood pressure.
In most scoliosis patients with pectus excavatum, intraoperative hypotension in the prone position can be managed with fluid loading and vasopressor administration. There have been 3 cases reported in which surgery was aborted because of severe hypotension.5–7 The primary pathomechanism of hypotension has been discussed as compression of the right ventricle by the sternum, which resulted in an increased inflow gradient, as demonstrated by transesophageal echocardiography.5–7 However, if the deformed chest wall directly compressed the right ventricle in the prone position, this would not fully explain the fact that hypotension is manageable in most scoliosis patients who also have similarly severe pectus excavatum, such as cases 2 and 3. Thus, we speculate that additional factors may have contributed to the marked hypotension.
Case 1 showed severe hypotension that could not be reversed in the prone position. On preoperative CT, the space made by the costal cartilages, the sternum, and the vertebral body was very narrow and the IVC lay directly on the aorta, forming the Y sign. Therefore, once the patient was turned to the prone position, the IVC was severely compressed by the aorta, the sternum, and the costal cartilages, which should cause a marked decrease in venous return and circulating blood volume. The IVC is well known as a highly compliant vessel.14 Given that the right ventricle is surrounded by the pericardium and myocardium, the IVC may be more susceptible to anterior compression by the sternum. We tried to confirm the Y sign in the previous 3 cases; however, the reports lacked CT scans illustrating the spatial relationship between the IVC and the aorta. If the Y sign was present in them, the pathomechanism would be the same as that in case 1, whereas if the Y sign was absent, hypotension may have resulted from right ventricular compression-induced arrhythmias or from the combined effect of other factors, including preoperative fasting, hydration status, and leg position, in addition to the inflow gradient caused by right ventricular compression.6,15,16
Ye et al. proposed detailed preoperative assessment in scoliosis patients with pectus excavatum or Marfan-like features, including a prone position test or echocardiographic evaluation in both the supine and prone positions.11 However, particularly in cases such as case 1, in which CT reveals the Y sign, a prone position test before pectus excavatum repair may itself carry a substantial risk of hemodynamic deterioration. In such patients, it may be reasonable to proceed first with pectus excavatum repair, followed by scoliosis surgery. In fact, in case 1, we performed a prone position test after pectus excavatum repair. Although a prone position test before pectus excavatum repair may provide useful hemodynamic information, it should be performed with adequate vascular access and an arterial line in a setting that allows immediate management of marked hypotension.
This report has some limitations. First, because the proposed association between the Y sign and refractory prone position hypotension is based on a single case, sensitivity and specificity are unknown. The Y sign could theoretically be present in patients who do not develop refractory hypotension. In addition, the limited case number precluded establishment of a protocol for a prone position test. Therefore, the indications and protocols for this test require validation in larger cohorts. Second, our assumption was based solely on preoperative CT scans obtained in the supine position. Although direct evaluation of the IVC and right heart with transesophageal echocardiography in the prone position would have been preferable, in case 1 the patient’s blood pressure dropped immediately to 25/17 mm Hg after prone positioning, necessitating prompt return to the supine position and making further evaluation in the prone position difficult. Third, the Y sign may be applicable only to scoliosis patients with Marfan syndrome because the thoracic cage is more compliant in this syndrome. However, even in patients without Marfan syndrome, the spatial relationship among the costal cartilages, the great vessels, and the vertebral body should be carefully evaluated when severe pectus excavatum is present, because severe hypotension in the prone position has also been reported in such patients.5,7
Lessons
The Y sign may serve as an anatomical indicator for preoperatively estimating the risk of refractory hypotension occurring in the prone position. If the Y sign is identified, pectus excavatum repair before scoliosis surgery may be considered to reduce this risk. If a prone position test is performed before pectus excavatum repair, careful preparation and close hemodynamic monitoring are essential.
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: Takahashi, Kawaharada, Yahata, Hashimoto, Sugawara, Aizawa. Acquisition of data: Takahashi, Kawaharada, Yahata, Hashimoto, Kusakabe. Analysis and interpretation of data: Takahashi, Kawaharada, Yahata, Onoki. Drafting the article: Takahashi, Kawaharada, Yahata, Aizawa. Critically revising the article: Takahashi, Hashimoto, Aizawa. Reviewed submitted version of manuscript: Takahashi, Yahata, Onoki, Ishikawa. Approved the final version of the manuscript on behalf of all authors: Takahashi. Statistical analysis: Takahashi. Administrative/technical/material support: Takahashi, Sugawara. Study supervision: Takahashi, Onoki, Aizawa.
Correspondence
Kohei Takahashi: Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan. kohei.takahashi.c1@tohoku.ac.jp.
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