3.1. Liver
The liver is the most common organ involved in ADPKD, with liver cysts present in more than 90% of ADPKD patients. Current literature generally considers Polycystic liver disease (PLD) as the existance of over 20 liver cysts [
55]. PLD development is linked to structural alterations in the biliary tree, resulting in cyst formation, that normally occour early in the disease process [
56,
57,
58]. Symptoms are due to cysts growth and tipically occours in adulthood. [
59]. Cysts distribution could be focal or diffuse to the whole organ. [
60] The prevalence of PLD has increased due to factors such as longer life expectancy and improved kidney survival. PLD associated with ADPKD is genetically distinct from isolated PLD but follows a similar clinical course, featuring hepatomegaly caused by multiple cysts while preserving liver function [
61,
62,
63]. Several risk factors plays a role in the formation of more severe PLD. These include the severity of the renal lesion, feminine gender, exogenous estrogen exposure and repeated pregnancies. Although both males and females with ADPKD have a similar overall prevalence of PLD, cysts in females tend to be bigger and to appear earlier. The growth of hepatic cysts in females may be accelerated due to steroid hormones, as evidenced by the association between postmenopausal estrogen and selective enlargement of hepatic cysts and parenchyma [
63,
64,
65,
66]. Furthermore, studies have shown that 58% of females older than 48 years with severe PLD, experience a regression in liver volume, while the liver continues to enlarge in males. Therefore, women with severe polycystic liver disease should refrain from hormone replacement therapies and contraceptives containing estrogen [
67,
68,
69]. The risk of developing severe PLD is is not influenced by the ADPKD genotype but is associated with the gravity of renal disease [
64]. Symptoms in PLD depends on the number, size, location, and distribution of cysts, which contribute to hepatomegaly. Liver cysts often remain asymptomatic and rarely lead to hepatic function impairment. However, approximately 20% of these patients experience symptomatic PLD. Symptoms are typically associated with progressive liver enlargement and may include pain, dispepsia, gastroesophageal reflux, and, when the size compress the portal vein can lead to portal hypertension and ascites. Extensive enlargement of the liver can exert pressure on the nearby gastrointestinal tract, blood vessels, and diaphragm, resulting in diverse symptoms. Moreover, complications like cyst hemorrhage, rupture, or infection may give rise to additional symptoms. Highly symptomatic PLD has become more common due to the increased life expectancy of ADPKD patients[
70,
71,
72,
73,
74,
75,
76,
77].
The most used clinical classifications on PLD were written by Gigot and Schnelldorfer [
78,
79] (respectively
Table 1 and
Table 2)
The Gigot classification serves to differentiate between phenotypes by considering the number, the size and the amount of liver involved [
78]. Gigot classification relies on imaging studies, but has the limits not to include symptoms and not to evaluate advancement of the condition.
Table 1.
Gigot Classification.
Table 1.
Gigot Classification.
The Schnelldorfer classification incorporates factors such as the quantity and size of cysts, the volume of remaining liver parenchyma, the input and output of previously preserved liver segments, and the presence of symptoms [
74].
Table 2.
Schnelldorfer Classification.
Table 2.
Schnelldorfer Classification.
For the assessment of PLD symptoms, two specific questionnaires have been created and validated: POLCA (PLD complaint-specific assessment) [
80] and PLD-Q (PLD questionnaire) [
81]. Following completion, the total score is determined by summing individual symptom scores, with a higher total score indicating a greater disease burden. Patients actively participated in the development of PLD-Q, unlike the development of POLCA, resulting in distinct sets of items. Nevertheless, both questionnaires are applicable for gauging disease burden and evaluating changes in symptom burden post-treatment. Since treatment is recommended exclusively for symptomatic patients with hepatomegaly, both instruments can serve as novel clinical endpoints [
82]. Liver volume, measured through CT or MRI volumetry using (semi-)automatic software, acts as a prognostic marker impacting both symptom burden and quality of life [
82]. Two classifications are available to differentiate between mild, moderate, and severe phenotypes based on htTLV [
62,
83]. In the classification introduced by Hogan MC et al., mild PLD is arbitrarily defined as height-adjusted total liver volume (htLV) <1000 mL/m, while htLV between 1000 - 1800 mL/m is considered moderate PLD. They designate severe PLD as htLV >1800 mL/m, aligned with the plateauing of height-adjusted liver parenchymal volume (htLPV) at this cutoff point. This point approximately corresponds to height-adjusted liver cyst volume (htLCV) >700 mL/m [
62]. In the classification put forth by Kim H et al., they categorize patients with PLD into three groups based on their htLV: no or mild PLD (htTLV < 1.600 mL/m), moderate PLD (1.600 ≤ htLV < 3.200 mL/m), and severe PLD (htLV ≥ 3.200 mL/m) [
83].
In the management of PLD, therapeutic approaches are tailored to the individual patient based on their specific needs. One common complaint among patients is related to symptoms caused by progressive hepatic enlargement. The only medical therapy that has been shown to reduce liver dimension and improve quality of life in these symptomatic patients is the use of somatostatin analogues (SAs). Somatostatin hinders the production of cyclic adenosine monophosphate (cAMP) in cystic cholangiocytes. This compound is excessively produced in PLD and contributes to cellular growth and cystic fluid production. By decreasing fluid secretion and cell proliferation, SAs can reduce liver volume. Studies have demonstrated that six months of lanreotide injections can lead to a decrease in liver volume, and extending the treatment for an additional six months may lead to the stabilization of hepatic volume. Conversely, the use of vasopressin receptor 2 (V2) antagonists does not seem to reduce liver volume [
84,
85,
86].
When symptoms are caused by a dominant cyst, patients may be eligible for aspiration sclerotherapy (AS). AS is a less invasive procedure that entails puncturing the cyst with radiological guidance, aspirating the cyst fluid, and then injecting a sclerosing agent. This process aims to reduce the cyst volume [
87].
In cases where symptoms are caused by multiple larger cysts and if these cysts are accessible, fenestration can be considered. Fenestration involves both aspirating and surgically deroofing liver cysts. However, this approach is suitable only when the distribution of cysts permits access [
82].
If the distribution of cysts does not allow for AS or fenestration, segmental hepatic resection may be considered. This procedure is reserved for cases of symptomatic and severe hepatomegaly, where a few liver segments are significantly affected by multiple cysts while other segments are less affected. It is important to note that segmental hepatic resection carries a higher risk of perioperative complications and may complicate future liver transplants due to the formation of adhesions [
82].
Liver transplantation is the only curative treatment for severe and advanced cases of PLD. However, only a minority of patients will qualify for this intervention. Patients with massive hepatomegaly who suffer from severe malnutrition, low serum albumin levels, sarcopenia, or severe and recurrent complications such as cyst infections or portal hypertension may be considered for liver transplantation. The Model for End-Stage Liver Disease (MELD) score, which assesses the three-month prognosis in patients with liver failure, is an important tool for selecting patients for liver transplantation. In cases of ADPKD with severe renal impairment, combined liver-kidney transplantation should be considered [
82].
It's worth noting that the choice of therapy should be made in consultation with healthcare professionals who specialize in the management of PLD, taking into consideration the individual patient's condition, symptoms, and other factors.
3.3. Other Involvements
In addition to the more commonly known manifestations of ADPKD, such as liver and kidney cysts, there are several other extrarenal manifestations that can occur in ADPKD patients.
Arachnoid membrane cysts, although rare, can occur in approximately 8% of ADPKD patients. These cysts are typically asymptomatic and found incidentally, but they may increase the risk for subdural hematomas, which are collections of blood between the brain and its outermost covering.
Spinal meningeal diverticula, which are outpouchings of the spinal meninges, can occur more frequently in ADPKD patients. However, they rarely present with intracranial hypotension, which is a condition characterized by low cerebrospinal fluid pressure due to a leak [
93,
94].
Cysts in the seminal vesicles are observed in approximately 40% of male ADPKD patients. While they are rarely responsible directly of infertility, they can contribute to defective sperm motility, leading to the same result. Prostate median cysts near the ejaculatory ducts have also been associated with ADPKD [
95].
There is evidence suggesting a higher prevalence of bronchiectasis, a condition characterized by damage and widening of the airways in the lungs, in ADPKD patients [
96].
Colonic diverticula, which are small pouches that develop in the colon, as well as abdominal wall and inguinal hernias, have been documented to occur more frequently in patients with ADPKD. However, it's important to note that the studies supporting this association are dated, and there is a lack of recent data available on this topic [
97,
98,
99,
100].
Contrary to some reports, ovarian cysts are not associated with ADPKD [
101].
It's worth noting that additional research is necessary to gain a comprehensive understanding of the prevalence, clinical consequences and underlying mechanisms of these extrarenal manifestations in ADPKD.