RC occur commonly in the renal cortex, with an exophytic development, although the etiology is yet to be fully established. RC is one of the most common benign lesions of the kidneys, and occurring with a frequency greater than 50% over the age of 50 years [1-3]. Most are simple RC and are usually detected incidentally on imaging. They are occasionally large enough to be palpable on routine clinical examination or by the patient himself. The origin of RC is in renal tubules, exactly from the diverticulum of the distal convoluted tubule [4]. Proliferation of tubule epithelial cells modulated by endocrine, paracrine, and autocrine factors is a major element in the pathogenesis of RC diseases [5]. However, majority of the RC are < 3 cm in size [6]. They may occur well within a kidney or on its surface, usually oval or round in shape, they have a smooth outline lined by a single layer of flattened epithelium [7]. The pathogenesis of cysts presenting at a later stage is less clear. If developmental, they may represent abnormalities of earlier generations of uriniferous tubules persisting as cystic collections. If acquired, they may represent renal tubular obstruction secondary to focal ischaemia and inflammation, factors that can produce epithelial cysts experimentally [8]. Giant RC are fluid-filled sacs that can form in the kidneys. Although they are often benign and asymptomatic, large cysts can cause symptoms such as flank pain, infection, or bleeding.

Furthermore, the clinical significance of giant renal cysts presents a varied range of symptoms, including: severe pain (due to distension of the renal capsule, resulting in dull, chronic pain in the flank); hypertensive compression (compression of the renal artery may cause secondary arterial hypertension); hydronephrosis (compression of the calyceal system or ureter can obstruct urinary flow, leading to parenchymal distress); risk of cyst rupture or hemorrhage (large cysts are exposed to external trauma, with a risk of spontaneous rupture or intracystic bleeding).

The International reference classification for the RC is the —Bosniak classification‖ (updated in 2019), which assesses the risk of malignancy based on morphological characteristics on contrast-enhanced CT, and cystic lesions are divided into five categories based on their visible characteristics (presence of septa, wall thickness, calcifications and how they react to contrast enhancement):

• Bosniak type I cysts are so-called simple benign cysts, with thin walls and no septa, calcifications, or solid components. Their contents have the same density as water.
• Bosniak type II cysts are minimally complicated cysts: they may have thin septa or fine calcifications; the content may be slightly denser than water but without contrast medium uptake. These are also benign cysts that do not require any special measures. In some situations —when the diagnosis is based only on US examination— may request a more accurate examination (such as a CT scan with contrast medium or an MRI). Once the diagnosis has been confirmed, no further investigations are necessary.
• Bosniak type IIF cysts differ from category II in that they have a greater number of septa with possible thickening, minimal calcifications, and/or slight contrast uptake. In 5-10% of cases, these cysts may be malignant, and therefore follow-up monitoring is recommended for the next 5 years after the initial diagnosis.
• Bosniak type III cysts are indeterminate cystic formations that often have thick walls or septa and take up contrast medium. They are malignant in 60-80% of cases and, in the absence of reassuring medical history data such as previous trauma or kidney infection, usually require histological data obtained through transcutaneous biopsy or exploratory surgery.
• Bosniak type IV cysts are highly suspicious for malignant neoplasia. These cysts contain obvious solid areas that can take up contrast medium. In these situations, surgery to remove the lesion should always be considered.

In our case, we observed giant RC of type 1 (according to Bosniak classification). In addition, in our long experience, in particular with CT scans, we have rarely encountered giant simple cysts which are not part of the findings of polycystic kidneys (which have a completely different approach) [9]. The RC that we have described in our case report are simple RC and represent the largest ones we have ever described in our radiological activity (13 cms).

CT-urography is a specialized CT application dedicated to the study of the urinary tract, capable of simultaneously analyzing the kidneys, ureters, and bladder (all-in-one study‖). UroCT scan is indicated for: diagnosis and staging of urinary tract tumors; evaluation of renal vascular abnormalities and congenital malformations; diagnosis of inflammatory/infectivous diseases; characterization of renal cysts; valuation of renal trauma.

Diagnosis of RC is made through imaging tests, such as US and CT. Simple cysts don’t require treatment, but giant cysts that cause symptoms (or have complex characteristics) may require regular monitoring and, in some selected cases, a surgical treatment (such as percutaneous or laparoscopic removal).