Mayo Adhesive Probability Score Is Associated with the Operative Time in Laparoscopic Adrenalectomy

Abstract

Background:

Laparoscopic adrenalectomy (LA) is the standard treatment for adrenal benign tumors, including primary aldosteronism (PA) or Cushing's syndrome (CS). Several obesity-related factors were associated with prolonged total operative time (OT), but perinephric fat characteristics were not assessed. We investigated whether the Mayo adhesive probability (MAP) score, which evaluates perinephric fat characteristics, was associated with OT for LA.

Methods:

This single-center, retrospective cohort study examined 141 consecutive patients who underwent LA for PA or CS. We reviewed patients' characteristics and OT. MAP scores were recorded using preoperative imaging. The correlation among characteristics data, MAP score, and OT was evaluated.

Results:

Overall, we assessed 82 women and 59 men. Adrenal tumors were found in 80 PA and 61 CS patients. There were 74 left-sided and 67 right-sided tumors. For all patients, the median age, body mass index, and tumor size were 56 years (interquartile range [IQR] 46–65), 24.1 kg/m² (IQR 21.7–26.8), and 19 mm (IQR 13–26), respectively. A total of 91 patients had MAP scores of 0, and 50 had MAP >0. The median OT was 183.5 minutes (IQR: 156–224 minutes) in the MAP >0 group and 162 minutes (IQR: 135–194 minutes) in the MAP = 0 group. In single variable analysis (unadjusted), MAP scores >0 and left-sided tumors were correlated with longer OT. Multivariable regression analysis revealed that this correlation was only significant for MAP scores >0.

Conclusions:

MAP score may be useful in preoperative planning for PA or CS patients undergoing LA.

Introduction

Laparoscopic adrenalectomy (LA) is the gold standard for the surgical treatment of small benign adrenal tumors, including those associated with primary aldosteronism (PA) or Cushing's syndrome (CS).^1–4 Compared with open surgeries, LA is associated with less estimated blood loss, less pain, faster convalescence, fewer incidences of ileus, shorter length of hospital stay, and a smaller scar.^5,6

Recently, the number of obese patients undergoing abdominal surgeries has been increasing worldwide, and obesity is considered to negatively impact surgical outcomes.^7,8 During LA, surgeons must contend with perinephric fat because of the anatomical location of the adrenal gland. Furthermore, several studies have revealed that obesity affects LA.^9–11 However, other studies showed opposing results.^12,13 Previous reports about the association of obesity with LA have used several parameters to reflect obesity, such as body mass index (BMI) or the amount of visceral fat determined from preoperative radiological findings. However, no study has reported the effects of the characteristics of visceral fat on LA.

The Mayo adhesive probability (MAP) score, based on the thickness of the posterior perinephric fat and perinephric fat stranding, is an imaging scoring system for predicting adherent perinephric fat for partial nephrectomy or simple donor nephrectomy.^14–16 In other words, the MAP score reflects the characteristics of perinephric fat, such as the thickness and stickiness of the fat itself. Thus, we investigated whether the MAP score was associated with total operative time (OT) in patients undergoing LA for PA or CS.

Materials and Methods

In this retrospective cohort study, we investigated 141 consecutive patients who underwent LA for PA or CS at our hospital between 2001 and 2019. Preoperatively, all patients underwent computed tomography or magnetic resonance imaging. This study was conducted in accordance with the ethical standards of the Declaration of Helsinki and was approved by the Regional Ethics Committee of the University of Yamanashi for Epidemiological Studies (Institutional Review Board Approval No. 2136). As this was a retrospective observational study, we received ethical approval to use an opt-out methodology, and thus, the need to obtain written informed consent was waived.

Surgical technique for LA

All patients with PA or CS were placed in the lateral full flank position. All the procedures were performed transperitoneally by multiple surgeons using the same technique with four trocars. The surgical procedures were carried out according to those reported previously.^1,3

Data collection and evaluation of the MAP score

We defined total OT as the time (in minutes) from skin incision to closure. Each patient's characteristics, namely age, sex, BMI, and sidedness of adrenal tumor, were collected from medical records. To evaluate the preoperative image (computed tomography or T1-weighted magnetic resonance images) for all patients, a blind review was performed by a single reviewer (S.K.). The maximum diameters of the adrenal tumor were calculated from the preoperative images for each patient. According to a previous study, the MAP score was recorded for each patient by measuring the posterior renal fat thickness and severity of perinephric stranding.¹⁴ Posterior perinephric fat thickness was defined as a direct line from the renal capsule to the posterior abdominal wall at the level of the renal vein for the kidney with the adrenal tumor. Posterior perinephric fat thickness was graded as follows: <1 cm = 0 points, 1.1–1.9 cm = 1 point, and >2.0 cm = 2 points.¹⁴ Perinephric stranding was defined as a linear area of soft tissue attenuation in the perinephric space. Stranding was graded as follows: no stranding = 0 points, thin mild stranding = 2 points, and diffuse stranding = 3 points.¹⁴ Finally, the MAP score was calculated for each patient as the sum of the values obtained for posterior renal fat thickness and perinephric stranding.

Statistical analyses

The Mann–Whitney U test for continuous variables and chi-square test for nominal variables were adopted for MAP score = 0 and MAP score >0. Single variable regression analysis was adopted for the unadjusted analysis of data on patients' characteristics, including MAP score and total OT. To investigate the association between MAP score and total OT, a multivariable regression analysis was performed with the following factors: age (continuous), sex (0 = female, 1 = male), BMI (continuous), sidedness (0 = right, 1 = left), PA/CS (0 = PA, 1 = CS), maximum diameters of the adrenal tumor (continuous), and MAP score (0, MAP score = 0; 1, MAP >0). Statistical significance was defined as a two-sided P value <.05. All statistical analyses were performed using SPSS^® version 22.0 (IBM Corp., Armonk, NY).

Results

There were 82 female and 59 male participants in this study. The median age was 56 years (interquartile range [IQR]; 46–65 years), and median BMI was 24.1 kg/m² (IQR 21.7–26.8 kg/m²) for all patients. Adrenal tumors occurred in 80 patients with PA and 61 patients with CS. There were 74 patients with left-sided tumors and 67 patients with right-sided tumors. The median maximum diameter of the tumors was 19 mm (IQR 13–26). A total of 91 patients had a MAP score of 0, and the rest (N = 50) had a MAP score of >0 (1 point: 16 patients; 2 points: 12 patients; 3 Points: 13 patients; 4 Points: 9 patients). The characteristics of all the patients in this study are shown in Table 1. No major perioperative complications (Clavien-Dindo grade ≥3) nor conversion to open surgery occurred in this population. Patients with MAP scores of >0 were predominantly male and had left-sided tumors and higher BMI than those with MAP score = 0. The median total OT for all patients was 169 minutes (IQR 143–208). The median total OT for patients with MAP = 0 and MAP >0 was 162 minutes (IQR; 135–194 minutes) and 183.5 minutes (IQR; 156–224 minutes), respectively (P = .002). In the unadjusted analysis, the single variable analysis showed that left-sided adrenal tumors (P = .038) and MAP of >0 (P = .001) were associated with the total OT (Table 2). In multivariable regression analysis, only a MAP score of >0 was significantly associated with prolonged total OT (P = .032) (Table 2).

Table 1.

Characteristics of All Patients that Underwent Laparoscopic Adrenalectomy for Primary Aldosteronism or Cushing's Syndrome

Data	All patients (N = 141)	MAP score = 0 (N = 91)	MAP score >0 (N = 50)	P ^a
Age	56 (46, 65)	56 (49.5, 68)	58.5 (52, 66)	.094
Sex (female/male)	82/59	65/26	17/33	<.001
BMI (kg/m²)	24.1 (21.7, 26.8)	22.5 (20.7, 25.6)	26.1 (24.4, 28.3)	<.001
Side (left/right)	74/67	41/50	33/17	.017
Adrenal tumor				.896
PA	80	28	52
CS	61	22	39
Maximum diameter (mm)	19 (13, 26)	18 (13, 25)	20 (12.8, 28)	.515

Age, BMI, and maximum diameter are represented as medians (interquartile range).

Mann–Whitney U test for continuous variables and chi-square test for nominal variables were adopted between MAP scores = 0 and MAP scores of >0.

BMI, body mass index; CS, Cushing's syndrome; LA, laparoscopic adrenalectomy; MAP, Mayo adhesive probability; PA, primary aldosteronism.

Table 2.

Results of Single and Multiple Regression Analysis

	Single regression analysis		Multiple regression analysis
	Coefficient (95% CI)	P	Coefficient (95% CI)	P
Age	0.231 (−0.5 to 0.9)	.505	−0.121 (−0.82 to 0.58)	.733
Sex	16.2 (−0.62 to 33.0)	.059	15.0 (−4.5 to 34.5)	.132
BMI	1.0 (−1.0 to 3.0)	.305	−0.284 (−2.4 to 1.9)	.794
Side	17.5 (1.0 to 34.1)	.038	14.9 (−1.9 to 31.7)	.081
PA/CS	9.9 (−7.0 to 26.7)	.249	14.0 (−8.9 to 2.0)	.227
Tumor size	0.5 (−0.4 to 1.3)	.258	0.133 (−1.0 to 1.3)	.814
MAP score	29.7 (12.9 to 46.6)	.001	22.2 (1.9 to 42.5)	.032

Sex: 0 = female 1 = male, Side: 0 = right 1 = left, PA/CS: 0 = PA 1 = CS.

BMI, body mass index; CI, confidence interval; CS, Cushing's syndrome; MAP, Mayo adhesive probability; PA, primary aldosteronism.

Discussion

In this study, multiple variable regression analysis showed that a MAP score of >0 was significantly associated with prolonged total LA OT for patients with PA or CS. Results of the single variable regression analysis (unadjusted) indicated that MAP scores of >0 and left-sided adrenal tumors were factors associated with prolonged total OT during LA.

Initially, the MAP score was developed and used for predicting adherent perinephric fat for robot-assisted partial nephrectomy.¹⁴ Recently, the MAP score has been reported to be associated with open and laparoscopic partial nephrectomy or donor nephrectomy.^15–17 The MAP score consists of two factors, namely posterior perinephric fat thickness and perinephric fat stranding. Posterior perinephric fat thickness is often used as a simple measurement for assessing the amount of visceral fat.¹⁸ However, the perinephric fat stranding is considered to indicate the stickiness of the fat itself. The existence of adherent perinephric fat means that adhesions are likely to occur between the renal capsule and the perinephric fat tissue; however, the stickiness of the perinephric fat may indicate that inflammation of the fat is the underlying process. Similar findings associated with inflammation are encountered in cases of pyelonephritis or ureteral obstruction.¹⁹ Inflammation of perinephric fat causes adhesion or abnormal proliferation of blood vessels in the fat. In general, adrenal glands are located in the perinephric fat in all populations, with or without obesity, so most LA procedures are conducted in the perinephric fat. Thus, we considered a MAP score of >0 as one of the factors that affected LA due to the characteristics of adhesive perinephric fat, such as thickness or stickiness.

Single variable regression analysis (unadjusted) revealed that, in addition to a MAP score of >0, left-sided tumors were associated with prolonged total OT in LA. In cases of left adrenal tumors, surgeons must mobilize the splenic flexure of the colon and the descending colon widely and be cautious because of the close proximity of the left adrenal tumors to the tail of the pancreas and the spleen. Left adrenal tumors also require dissection of the left renal hilum to control the left adrenal central vein. Thus, several studies reported that the OT of a left-sided LA is longer compared with a right-sided LA.^20–22 However, other studies have reported no differences between the left and right sides.^10,23,24 In this study, multiple variable regression analysis showed that location of a tumor on the left side did not affect the total OT. Regarding anatomical differences, left-sided adrenal tumors are more closely located to the kidney capsule than tumors on the right side. Thus, we speculated that left adrenal tumors might be more affected by adhesive perinephric fat than right adrenal tumors. In this study, when controlled for multiple regression analysis, the difference between the left and right sides was not revealed to be a significant factor.

BMI was not associated with a prolonged total OT of LA in single and multiple variable regression analyses in this study. BMI has been widely used as an indicator of the degree of obesity. Although obesity was divided into visceral and subcutaneous types, BMI does not accurately distinguish between these two types. Several studies have reported that the amount of visceral fat is associated with prolonged OT in laparoscopic abdominal surgery, including LA.^25,26 However, other studies have shown that BMI itself does not increase the surgical difficulty of LA.^10,12 Considering the structure, it was clear that the MAP score also reflected visceral fat. Therefore, we recognized that visceral fat, identified using the MAP score, was a more important factor than BMI in prolonging the total OT. Although single variable analysis showed that male sex appeared to be a factor of longer OT, the sex difference was not significantly associated with prolonged total OT on both variable analyses in this series. Regarding the effect of sex difference in LA's OT, several studies reported that female sex was a favorable factor associated with shorter OT during LA.^10,27 Generally, it is widely accepted that differences in body fat distribution are due to sex differences. Although women are believed to have a greater amount of subcutaneous fat, men have a greater amount of visceral fat. These insights may contribute to the fact that a MAP score of >0 tended to be more common in men than in women.¹⁴ Thus, when controlled for the MAP score, the difference in the total OT between women and men may decrease in a multiple variable analysis.

This study has some limitations. First, its retrospective nature is associated with the inherent potential for bias. Second, we only included cases using the transperitoneal approach and excluded the retroperitoneal approach. Finally, we did not enroll patients with other forms of adrenal tumors, such as pheochromocytomas and nonfunctional tumors. Future studies in which these other adrenal tumors are included will be required to validate our findings.

Conclusion

A MAP score of >0 was associated with prolonged total OT in LA for PA or CS. During the preoperative planning for LA in patients with PA or CS, MAP scores may be a good indicator for predicting the difficulty and expected duration of the procedure.

Footnotes

Authors' Contributions

S.K.: Data collection, Data analysis, Article writing. N.S.: Data analysis. H.N.: Data analysis. T.I.: Data analysis. R.F.: Data analysis. M.T.: Other (Supervision). T.M.: Data analysis, Article editing, Other (Supervision).

Acknowledgment

The authors thank Editage () for English language editing.

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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