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Prevention of conversion in posterior retroperitoneal adrenalectomy by measuring pre-operative anatomical conditions on cross-sectional imaging (computerised tomography or magnetic resonance imaging)
Simone Eichelberger1, Sebastian Schindera2, Christian Andreas Nebiker3
1 Faculty of Medicine, University of Basel, Basel, Switzerland
2 Department of Radiology, Kantonsspital Aarau, Aarau, Switzerland
3 Department of Surgery, Kantonsspital Aarau, Aarau, Switzerland
|Date of Submission||06-Feb-2022|
|Date of Decision||08-Apr-2022|
|Date of Acceptance||12-Apr-2022|
|Date of Web Publication||07-Jun-2022|
Christian Andreas Nebiker,
Department of Radiology, Kantonsspital Aarau, Tellstrasse 25, Aarau 5000
Source of Support: None, Conflict of Interest: None
Background: In addition to the common laparoscopic lateral transperitoneal adrenalectomy (LTA), the posterior retroperitoneal adrenalectomy (PRA) is becoming increasingly important. Both techniques overlap in their indication, resulting in uncertainty about the preferred approach in some patients. We hypothesise that by determining anatomical characteristics on cross-sectional imaging computerised tomography or magnetic resonance imaging, we can show the limitations of the PRA and prevent patients from being converted to LTA.
Methods: This retrospective study includes 14 patients who underwent PRA (n = 15) at a single institution between 2016 and 2018. Previously described parameters such as the retroperitoneal fat mass (RPF) were measured on pre-operative imaging. We compared data from one patient who had a conversion with those from 13 patients without conversion. Furthermore, we explored the influence of these parameters on the operative time.
Results: Conversion to LTA was necessary during 1 PRA procedure. Fourteen PRAs in 13 patients were successfully completed. The mean body mass index was 30 kg/m2 and the mean operation time was 98 min. One patient who underwent a conversion had a substantially higher RPF (25 mm) compared to the patients with successfully completed PRA (median: 5.5 mm [P = 0.001]). Furthermore, the operation time strongly correlated with the RPF (P = 0.004, r = 0.713).
Conclusions: Surgeons can use pre-operative imaging to assess the anatomical features to determine whether a PRA can be performed. Patients with an RPF under 14.3 mm can be safely treated with PRA. In contrast, LTA access should be considered for patients with a higher RPF (>25 mm).
Keywords: Adrenalectomy, minimally invasive surgery, posterior retroperitoneoscopic adrenalectomy, retroperitoneal fat mass
|How to cite this URL:|
Eichelberger S, Schindera S, Nebiker CA. Prevention of conversion in posterior retroperitoneal adrenalectomy by measuring pre-operative anatomical conditions on cross-sectional imaging (computerised tomography or magnetic resonance imaging). J Min Access Surg [Epub ahead of print] [cited 2022 Jul 3]. Available from: https://www.journalofmas.com/preprintarticle.asp?id=346836
| ¤ Introduction|| |
Minimally invasive adrenalectomy has become the gold standard for the surgical treatment of small, benign adrenal lesions. Two procedures have been established: the laparoscopic lateral transperitoneal adrenalectomy (LTA) and the posterior retroperitoneal adrenalectomy (PRA). The LTA provides the advantage of a familiar anatomy for abdominal surgeons. In addition, the laparoscopic procedure allows inspection of the abdominal cavity. However, access to the adrenal gland requires mobilisation of the liver or spleen, which can cause complications. In contrast, the PRA is becoming increasingly popular as it avoids entering the peritoneal cavity and allows direct access to the adrenal gland. Furthermore, PRA is preferred in bilateral adrenalectomy and in patients with previous abdominal surgery., However, due to the limited retroperitoneal space, this access may be too narrow for adrenal tumours with a diameter >6–7 cm., If the adrenal gland cannot be fully mobilised with additional trocars, conversion is necessary., The conversion rates range from 2% to 14%.,
Despite the abundance of published literature, no clear advantage of one surgical approach over the other has been demonstrated so far., Both techniques overlap in their indication, resulting in uncertainty about the preferred access in some patients., To choose the appropriate surgical access, it is necessary to quantify the anatomical limitations. For PRA, the narrow retroperitoneal space is the limiting factor. Agcaoglu et al. selected their patients according to an algorithm and described the anatomical parameters of the patients receiving PRA or LTA. Also based on anatomical parameters, Lindeman et al. created the Posterior Adiposity Index (PAI) that has been shown to be an independent predictor of operation time. To date, no study has evaluated the effect of the anatomical parameters on the rate of conversion from PRA to LTA.
The aim of this study was to determine the limits of PRA using these and additional parameters to enable the preferred access to be chosen preoperatively to prevent conversion. In addition, we describe the relationship between these parameters and the operation time to find a measure of the degree of technical difficulty.
| ¤ Methods|| |
This retrospective study includes 14 patients who underwent a PRA (n = 15) at a tertiary referral centre in Switzerland, between 2016 and 2018. Bilateral PRA was performed on one patient. Patients with multiorgan resection or an initial open procedure were excluded. The following clinical data were extracted and analysed from the hospital information system: sex, age, body mass index (BMI), previous abdominal operations, diagnosis, tumour size, side of the operation, bilateral versus unilateral involvement and operation time.
The techniques for laparoscopic PRA were performed according to a previously described standard. All operations were performed by the same two experienced surgeons.
Anatomical parameters were measured in millimetres using pre-operative imaging computerised tomography scan/magnetic resonance imaging (CT scan/MRI) and were defined as follows: distance between the dorsal border of the adrenal gland and the 12th rib tip (Ad–R); PAI, distance from skin to renal parenchyma through the 12th rib tip. This parameter has already been described by Lindeman et al.; thickness of retroperitoneal fat (RPF), defined as the largest distance between the kidney parenchyma and the posterior abdominal wall at the level where the renal vein joins the vena cava inferior; longitudinal distance between the upper pole of the kidney and the inferior border of the adrenal gland (K–A); longitudinal distance between the superior border of the adrenal gland to the 12th rib tip (As–R); and longitudinal distance between the 12th rib and the iliac crest (R–C). These parameters are shown in [Figure 1] and [Figure 2]. Different thicknesses of the subcutaneous layer were measured [Figure 3] and were defined as follows: sagittal thickness of the subcutaneous layer above the 12th rib tip (SR); sagittal thickness of the subcutaneous layer above the iliac crest (SL); thickness of the subcutaneous layer above the 12th rib tip (SR. cog), measured on the straight line to the centre of gravity (cog); and sagittal thickness of the subcutaneous layer between the cog and the lateral border of the body (S. cog–lat), measured at the level of the 12th rib tip. The data were examined independently of the site on which the operation was performed.
|Figure 1: Anatomical parameters: (a) Ad–R, dorsal border of the adrenal gland–12th rib tip (circle with dotted auxiliary line) distance (solid line); (b) PAI, Posterior Adiposity Index: skin–renal parenchyma distance (solid line) through the 12th rib tip; (c) RPF, retroperitoneal fat: kidney parenchyma–posterior abdominal wall distance (solid line) at the level where the renal vein joins the vena cava inferior, RPF: Retroperitoneal fat|
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|Figure 2: Anatomical parameters: (a) K–A, upper pole of the kidney (star with dotted auxiliary line)–inferior border of the adrenal gland distance (solid line); (b) As–R, superior border of the adrenal gland–12th rib tip (circle with dotted auxiliary line) distance (solid line); (c) R–C, 12th rib–iliac crest distance (solid line)|
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|Figure 3: Subcutaneous layer: (a) SR, subcutaneous layer (solid line) above the 12th rib tip; (b) SL, subcutaneous layer (solid line) above the iliac crest; (c) SR.cog, subcutaneous layer (solid line) above the 12th rib tip measured on the straight line to the centre of gravity (square with dotted auxiliary line); (d) S.cog–lat, subcutaneous layer (solid line) between the center of gravity (square with dotted auxiliary line) and the lateral border of the body, at the level of the 12th rib tip|
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We compared the data from one patient who underwent a conversion with 13 patients without a conversion. Furthermore, we explored the influence of these parameters on the operation time and excluded the patient who had a conversion from this analysis. One patient had to be converted because the adrenal gland could not be reached. Problem was that the angle between the instruments and the body surface was too small. Consequently, the instruments came to rest on the crista iliaca without reaching the adrenal glands. Therefore, we looked for different anatomical parameters that could have an influence on the operation.
The acquired data were entered into an Excel spreadsheet and statistically analysed with the help of RStudio (RStudio Team 2016, RStudio: Integrated Development for R. RStudion, Inc., Boston). Differences between the non-conversion and conversion groups were assessed with the one-sample Wilcoxon signed-rank test. Spearman correlation was used to test the correlation between the parameters and the operation time. Statistical significance was reached at P < 0.05.
| ¤ Results|| |
Conversion to LTA was necessary only in one patient. In 13 patients, 14 PRA procedures were successfully completed and formed the non-conversion group. Demographic and clinical characteristics of the study population and a comparison of the conversion and non-conversion groups are shown in [Table 1]. The mean age was 47 years (range: 34.4–66.3) and 8 of 14 patients were female. The mean BMI was 30 kg/m2 (range: 22.6–48.5) and the mean operation time was 98 min (range: 56–149). The mean tumour size was 3.3 cm (range: 0.7–7.0), and the most common indication for adrenalectomy in the study population was primary hyperaldosteronism. In addition, there were patients with pheochromocytoma, haemangioma, adrenal metastasis or hyperplasia in M. Cushing. The converted patient was slightly younger (40.8 years) than the non-conversion group, and his BMI of 40.8 kg/m2 was well above the median.
Comparison of conversion and non-conversion
The results of the comparison of conversion and non-conversion are listed in [Table 2]. The converted patient had a significantly higher RPF (25 mm) compared to the patients with successfully completed RPA (median: 5.5 mm, range: 1.5–14.2 mm) (P = 0.001). Interestingly, the patient with the conversion showed a significantly higher PAI (14.7 cm) than the non-conversion group (median: 5.7 cm, range: 3.2–13.3 cm) (P = 0.001). The longitudinal distance between the upper pole of the kidney and the inferior border of the adrenal gland (K–A) was significantly shorter in the patient with the conversion (−25.3 mm) than in the non-conversion group (median: 20.6 mm, range: 5.9–62.7) (P = 0.001). The largest difference in the thickness of the subcutaneous layer was the sagittal thickness above the iliac crest (SL) (75 mm compared to median: 14.9 mm, range: 8.4–86.1) and was found to be statistically significant (P = 0.001). Further, significant differences in the thickness of the subcutaneous layer on the back between the converted patient and the non-conversion group are listed in [Table 2]. In addition, the longitudinal distance between the superior border of the adrenal gland to the 12th rib tip (As–R) and the longitudinal distance between the 12th rib and the iliac crest (R–C) were statistically significantly longer in the converted patient (P = 0.009 and P = 0.041). Furthermore, we found a significantly higher BMI in the converted patient (40.8 kg/m2 compared to median: 28.4 kg/m2, range: 22.6–48.5) (P = 0.002) [Figure 4]. However, in the converted patient, the tumour size was rather small (1 cm compared to the median 4 cm range: 0.7–7).
|Figure 4: Retroperitoneal fat mass of the patient who underwent a conversion, MRI with the 25 mm long RPF (solid line). MRI: Magnetic resonance imaging, RPF: Retroperitoneal fat|
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Analysis of operation time
An analysis of the relationship between operation time and anatomical parameters showed that RPF (P = 0.004, r = 0.713) and the PAI (P = 0.011, r = 0.658) correlated most strongly with operation time. There was no statistically significant correlation between the BMI and the operation time (P = 0.096, r = 0.463) or other parameters.
| ¤ Discussion|| |
To date, there is no consensus regarding the preferred approach in the resection of benign adrenal tumours. A comprehensive adrenal tumour programme should be able to offer both options; however, patient selection criteria for a given approach have not yet been defined. The choice between LTA and PRA is relevant for patients with unilateral tumours <6–7 cm and without previous abdominal surgery.
During PRA, the failure to progress or the difficulty of creating or maintaining a pneumoperitoneum is among the most common reasons why a conversion occurs.,, In the prone position, very obese patients can compress their retroperitoneum and preclude sufficient retroperitoneal space.
Walz et al. described the need to convert two patients with a BMI >45 kg/m2 from PRA to an LTA due to the inability to create adequate working space and for this reason, this group does not recommend a retroperitoneal approach for patients with a BMI >45 kg/m2. Erbil et al. looked at the effect of RPF content on LTA and reported that visceral fat was superior to BMI in predicting surgical outcomes. Our study also identified RPF as a more accurate predictor of operation time and conversion risk than BMI for RPA.
Agcaoglu et al. were the first to investigate anatomical parameters in patients with RPA or LTA. Retrospectively, the surgeons preferred a PRA when the distance from Gerota's fascia to the skin was <5 cm and the 12th rib was rostral to the level of renal hilum. Furthermore, the total operation time correlated with the thickness of the perirenal fat in the PRA group. Based on these findings, Lindeman et al. created the PAI that proved to be a predictor of operation time. The PAI is the distance from skin to renal parenchyma through the 12th rib tip.
Our study supports these findings; however, we found that RPF showed a stronger correlation with operation time than PAI. In addition, the patient with conversion to the LTA had a 25-mm-thicker RPF than the nonconverted group (median: 5.5 mm). No conversion was required in patients with an RPF below 14.3 mm.
Furthermore, the sagittal thickness of the subcutaneous layer above the 12th rib (SR) was significantly higher in the converted patient. It seems plausible that the thickness of the subcutaneous layer makes access to the retroperitoneal space even more difficult due to the narrower insertion angle and the limited mobility of the instruments.
We recommend caution in obese patients where the adrenal gland is cranial to the kidney. This parameter showed no correlation with operation time, but only in the converted patient was the adrenal gland (25.3 mm apart) located completely above the upper pole of the kidney.
A clear limitation of the study is the low number of patients. We also used two different imaging techniques, CT and MRI, which, however, should not influence the results. In addition to the compression of the subcutaneous layer during imaging, the organs moved ventrally in the prone position. Therefore, the size of the pneumoperitoneum can only be estimated to a limited extent. Further prospective studies are needed to validate our findings.
| ¤ Conclusion|| |
Our data demonstrate that surgeons can use the anatomical measurements on pre-operative imaging (CT or MRI) to determine whether PRA can be performed without conversion. Patients with an RPF <14.3 mm can safely be treated with PRA. In contrast, LTA access should be considered for patients with a very high RPF (25 mm or more). However, if the RPF is between 14.2 and 25 mm, the ideal approach remains unclear. Within this range, we recommend using the thickness of the subcutaneous layer (SL) and the distance between the kidney and adrenal gland (K–A) to choose the more suitable surgical access.
Disclosure and ethics statement
The authors declare no conflict of interest and we received no financial support for research. The study was approved by the local ethics committee (Ethikkomission Nordwest-und Zentralschweiz, Project-ID: 2019-01147).
The authors acknowledge Philipp Schütz, MD for his advice concerning the statistical analysis. They also thank Susanne Rogers, MD for her English editing.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]