Psoas major muscle, also known as the large psoas muscle, is a long pike shaped muscle that originates from both sides of the lumbar vertebrae and is mostly caused by inflammation. It can be seen in yellow granulomatous pyelonephritis, where the perinephric fascia is thickened and adhered due to inflammatory infiltration, and the inflammation can extend widely to the perinephric tissues, causing swelling and adhesion or abscess formation in the affected psoas major muscle, which can involve the liver, spleen, colon, inferior vena cava, duodenum, etc., and even form skin fistulas. The examination items for swelling of the psoas major muscle: 1. MRI MRI, also known as magnetic resonance imaging, is the use of the principle of nuclear magnetic resonance, through the application of gradient magnetic field detection of the emitted electromagnetic waves, according to which the internal structure of the object can be drawn into the image. Magnetic resonance imaging (MRI) has diagnostic significance for neurological lesions, spinal cord lesions, cardiovascular lesions, abdominal and pelvic organ examinations, and joint and soft tissue lesions. 2.CT CT examination of the kidneys is a method of examining the kidneys through CT. The purpose is to check kidney diseases, such as stones, inflammation, tumors, etc. CT can be used for the examination of many kinds of diseases, and it has auxiliary significance to the diagnosis of diseases. 3.MRI examination of kidney MRI can identify the location, size, shape and invasion range of the mass; it can identify the mass as cystic, substantial or fatty, which is more sensitive and qualitatively accurate than CT.