Table 5. Retroperitoneal approach: surgical difficulty comparison (including open converted cases).

	2009–2012	2013–2015	2016–2018	P value
Number of cases	90	110	191
Operation side (right:left)	46:44	56:54	77:114	0.106
Diagnosis (number of cases) †				0.037
Hyperaldosteronism	30	38	64
Pheochromocytoma	14	20	20
Cushing’s syndrome	18	24	52
Non-functioning incidentaloma	23	19	49
Non-functioning symptomatic tumor	4	1	2
Metastatic cancer	1	8	4
Tumor size (cm)	2.78±1.54	2.64±1.48	2.61±1.55	0.668

^†Fisher’s exact test.