XGP is a rare and distinct form of chronic pyelonephritis that usually occurs in the background of a urinary tract obstruction caused by renal calculi and recurrent chronic infections [5]. Its most significant histological feature is the existence of lipid-laden foamy macrophages [6]. XGP can occur at any age, but has the highest incidence in immunocompromised middle-aged women. XPG’s pathology usually presents unilaterally, but occasionally bilaterally in the kidneys. The latter prognosis is worse than the former and is likely due to bilateral renal function impairment [7]. There are usually no characteristic symptoms of XGP.

In our case, there was a history of flank pain, weakness, low-grade fever, urinary tract infections, absence of dysuria, weight loss, nephrolithiasis, renal angle tenderness, and a palpable lump. However, renal complications of ADPKD can also include nephrolithiasis, infection, and pain [8]. Therefore, the preoperative diagnosis of XGP with ADPKD is challenging. This is an extremely rare case reporting XGP with ADPKD.

Imaging helped with the preoperative diagnosis of XGP. According to the imaging, XGP can be divided into two anatomic forms: the diffuse form and the focal form [9]. The diffuse form is the most common. The typical imaging signature is the “bear paw sign,”in which multiple rounded foci filled with lipid-laden macrophages dilated the renal pelvis and calices [10]. Our case did not observe the bear paw sign. Depending on the inflammation’s progression, XGP starts in the renal parenchyma and the perirenal adipose space and subsequently spreads to adjacent structures or the retroperitoneum, culminating in the formation of renoduodenal fistula, pancreatic adhesions or nephrocutaneous fistula [11,12,13]. Preoperative imaging should thoroughly evaluate the relationship of kidneys to the surrounding tissue and organs in order to prevent serious complications [14].

XPG has a close resemblance, clinical symptoms, and imaging findings to that of a renal tumor in the focal form, also known as the pseudotumor form [15]. Ultrasonic manifestations of renal cell carcinoma are round or oval solid space-occupying lesions, with complex internal echoes, but generally smooth edges and clear boundaries, and some of them can see low vocal cords. The focal form of XGP is a chronic inflammation, and the boundary of the lesions is vague. It can be preliminarily identified in combination with signs such as renal calculi and perirenal involvement.

In this case, the initial presumptive diagnosis was a cystic renal cell carcinoma with polycystic kidney disease. These results raised concerns about renal malignancies, including unequivocal enhanced masses in the right kidney imaged using CEUS and contrast-enhanced CT,the FDG-avid revealed the thickened walls in the cystic mass with the FDG-avid post-peritoneum lymph nodes imaged via 18F-FDG PET/CT. Meanwhile, this patient had a history of bilateral ADPKD, which further increased the preoperative diagnostic difficulty. However, if the focal XPG combined with ADPKD is misdiagnosed as a malignant renal tumor, it will lead to an unnecessary surgical resection. For focal XPG combined with ADPKD, especially patients with severe renal insufficiency or a solitary kidney we advocate an ultrasound-guided puncture biopsy of the focal mass in order to make a clear diagnosis before operation[16,17,18].

Beyond that, XGP might also mimic other renal tumors, renal tuberculosis, and renal abscesses. Nevertheless, lipid-laden foamy macrophages are typical and necessary for the diagnosis of XGP, and can be histopathologically differentiated from other renal diseases.

The recommended treatment of XGP includes surgery and antibiotic therapy. Surgery includes both an open and laparoscopic nephrectomy. Asali et al. [19] concluded that laparoscopic nephrectomy should be considered an initial approach for XGP. The indications for laparoscopic nephrectomy should be extended to these patients. Antibiotic therapy can serve as an alternative therapy for small and focal lesions.

In conclusion, XGP with polycystic kidney disease is extremely rare. The purpose of this case study is to emphasize that XPG should be taken into consideration in the differential diagnosis of renal masses with polycystic kidney disease, even in the absence of characteristic clinical symptoms. Careful preoperative examination plays an important role in choosing the treatment direction and operation mode.