Simple Cysts of the Kidney: A Review and Update
Authors: Kodzo-Grey Venyo Anthony 
Published: March 2022

Based upon radiology imaging features of cysts of the kidney, cysts of the kidney tend to be classified as (a) simple kidney cysts which fall under the sub-classification of Bosniak Category I and II cysts, or (b) complex renal cysts which tend to be classified as belonging to Bosniak Category III and IV cysts, or intermediate category kidney cysts which are sub-classified as belonging to Bosniak Category IIF group of renal cysts. Simple renal cysts represent benign kidney cysts that quite often tend to be asymptomatic so that generally they tend not to require any treatment and they tend to be managed conservatively or expectantly. Nevertheless, if a simple cyst of the kidney becomes symptomatic, it does need to be treated and percutaneous drainage of the kidney cyst combined with sclerotherapy or surgical treatment tends to be selected. Additionally if the size of a simple renal cysts is increasing clinicians often undertake treatment of the cysts to provide reassurance to their patients. There is no global consensus opinion regarding the treatment of simple kidney cysts. Some of the manifestations of simple renal cyst include: (a) Asymptomatic cysts of the kidney that are found incidentally upon radiology imaging investigation of a different condition, (b) a palpable lump/mass in the loin, (c) abdominal / loin pain, (d) hypertension and during investigation of the hypertension the simple cyst or cysts are found, (e) visible haematuria, (f) non-visible haematuria, (g) increasing abdominal girth, (i) loss of appetite, (j) nausea and vomiting, (k) constipation, (l) weight gain and other non-specific symptoms. Diagnosis of simple cysts tend to be undertaken and distinguished from complex renal cysts or cystic renal tumours based upon imaging features of radiology imaging options including non-contrast ultrasound scan of the renal tract, contrast-enhanced ultrasound scan (CEUS) of the renal tract, non-contrast computed tomography (CT) scan of the renal tract, contrast-enhanced computed tomography (CECT) scan of the renal tract, non-contrast magnetic resonance imaging (MRI) scan of the renal tract, and contrast-enhanced magnetic resonance imaging (CEMRI) scan of the renal tract. Treatment options for simple kidney cysts have tended to involve various options including (a) conservative treatment / leave alone, (b) Expectant management with periodical radiology imaging for follow-up assessments, (c) Per-cutaneous aspiration of the kidney cyst(s)/drainage of the cyst(s), percutaneous aspiration / drainage and sclerotherapy of the kidney cysts, (d) selective renal artery angiography and super-selective embolization of the simple renal cyst(s), (e) marsupialization / decortication of the simple renal cysts by the open method or laparoscopy technique, (f) marsupialization / decortication of the simple renal cysts by the open method or laparoscopy technique plus wadding of the operation site with omental / fat interposition, (g) partial nephrectomy by the open or laparoscopy approach to excise the cyst(s), (h) nephrectomy by the open or laparoscopy technique for large simple polycystic kidneys. Complications that could be associated with aspiration / drainage and sclerotherapy of simple renal cysts include bleeding, infection, and pain plus recurrence and persistence of renal cysts and with regard to cysts in the upper pole of the kidney could be ensued by accidental injury to the spleen and basal lung atelectasis. Embolization of the arterial branch of large and multiple renal cysts could also be associated with post-embolization phenomenon (Wunderlich’s syndrome) including general malaise, fever, loss of appetite and raised white blood cell count that may mimic infection as well as last for a few weeks and this can be prevented by administration of pre-procedure and peri-procedure steroids for a short time. Other possible treatment options for simple kidney cysts that have not been tried include radiofrequency ablation of the residual cyst pursuant to aspiration / drainage / sclerotherapy of the renal cyst, and irreversible electroporation of the residual kidney cyst pursuant to aspiration/drainage/sclerotherapy of the kidney cyst. Considering that the morbidity that tends to be associated with open surgical treatment and laparoscopy treatment options for the management of simple kidney cysts tends to be worse in comparison with per-cutaneous aspiration/drainage/sclerotherapy, generally most clinicians tend not to undertake treatment of kidney cysts initially by the open and laparoscopy procedures. Considering that persistence / recurrence of simple renal cysts can occur or do occur pursuant to percutaneous aspiration/drainage/sclerotherapy of simple kidney cysts, it would be suggested that the undertaking of percutaneous angiography and super-selective embolization of residual simple renal cysts pursuant to the initial treatment or utilization of post-procedure radiofrequency ablation or irreversible electroporation of simple kidney cysts would help reduce the incidence of recurrent and persistent simple kidney cysts and if this is undertaken hopefully the need to undertake open or laparoscopy procedures for dimple kidney cysts would be reduced. There is a need to undertake a global multi-centre trial of various treatment options for simple kidney cysts in order to ascertain the best treatment option with durable long-term outcome of non-recurrence or persistence of the renal cyst(s).