What Is Caroli Disease and How Is It Classified?
Caroli disease is defined as congenital dilation of intrahepatic bile ducts without any definite obstruction. Caroli disease is often included in Todani’s classification of choledochal cysts and is categorized as type 5. It is also included in the spectrum of fibropolycystic diseases along with autosomal dominant polycystic liver disease, congenital hepatic fibrosis, and biliary hamartoma. These are genetic disorders that cause hepatic parenchymal fibrosis and intrahepatic biliary dilatations due to the persistence and/or aberrant remodeling of the embryonic ductal plate (ductal plate anomaly). Fibrocystic kidney diseases are frequently associated.
What Is the Pathogenesis of Caroli Disease?
Caroli disease arises due to aberrant remodeling of the embryonic ductal plate structures. Involvement of larger bile ducts produces Caroli disease, while congenital hepatic fibrosis affects smaller bile ducts. When both large and small bile ducts are involved, it is known as Caroli syndrome.
What Are the Clinical Manifestations of Caroli Disease?
Caroli disease usually presents during the second or third decade of life but may present earlier, too. Males and females are equally affected. Patients often report a classic triad of abdominal pain, right hypochondrial mass, and jaundice. Hepatic markers such as bilirubin, SGPT (serum glutamic pyruvic transaminase), and ALP (assistant loco pilot) are normal or just slightly increased.
How Is Caroli Disease Diagnosed?
Imaging:
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Ultrasound is often the first imaging and is ideal for suggesting diagnosis, follow-up, and interventions. The confirmation of this disease is mainly done by ERCP (endoscopic retrograde cholangiopancreatography) or MRCP (magnetic resonance cholangiopancreatography). MRCP has the additional benefit of being non-invasive and can visualize extra-luminal findings, too. However, ERCP is the gold standard due to its higher resolution than MRCP and also allows immediate therapeutic intervention if required. CT (computed tomography) and/or MRI (magnetic resonance imaging) help to detect developing cholangiocarcinoma (ten percent risk). Abdominal X-rays are often done, but provide no specific information other than bulging flanks accompanied by prominent and enlarged hepatic shadow.
Findings:
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Enlargement of the liver and spleen are most frequently identified.
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Focal, segmental, or diffuse dilatation of the intrahepatic biliary tree is the core finding and is seen in all imaging modalities. The dilated tree demonstrates communication with the rest of the biliary system and has the same appearance as bile on all imaging modalities (differentiates from biliary hamartoma). Gross dilatation may produce the appearance of large multiloculated cystic lesions.
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The central dot sign is quite a characteristic of Caroli disease. It constitutes a normal-diameter portal radicle surrounded by a dilated bile duct. The bile duct shows no enhancement after administration of IV (intravenous) contrast, nor does it show any color flow on Doppler ultrasound studies. In contrast, the portal radicle containing the vessels exhibits both color flow on Doppler as well as contrast enhancement on CT or MRI images.
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The gall bladder may be dilated in some cases, while the kidneys, pancreas, and other organs exhibit no abnormal findings.
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Intraductal echogenic septations and/or distension of the gall bladder or common bile duct may also be found in some cases.
What Are the Complications of Caroli Disease?
The abnormally dilated biliary channels may develop intraductal sludge or calculi in up to 95 percent of cases, which can be seen as fluid-debris levels on ultrasound, CT, and MRI.
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Cholangitis: The dilated channels and branches may become inflamed or infected. This is seen on ultrasound as irregular contour and wall-thickening of the biliary tree. These may also be accompanied by internal fluid-fluid or fluid-debris levels, which appear echogenic on ultrasound and may show contrast enhancement on CT or MRI scans.
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Cholangitis Abscess: The infections can turn into localized pus collections along the bile ducts. This would appear as erratic wall-thickening along the intrahepatic biliary channels, interspersed with multiple loculated fluid collections that show strong peripheral enhancement after administration of IV (intravenous) contrast.
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Cholangiocarcinoma: Ten percent of patients with Caroli disease may eventually suffer from cholangiocarcinoma. On CT or MRI, it would be frequently identified as a luminal mass that shows moderate heterogeneous contrast enhancement with delayed washout. This may be accompanied by thickening and focal enhancement of the duct wall.
What Are the Various Conditions Associated With Caroli Disease?
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Medullary Sponge Kidney (80 percent): There may be ectopic renal tubules with calculi, as well as calcification or calcinosis involving the renal medullae.
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Polycystic Kidney (80 percent): It is an inherited disorder in which multiple cysts are formed in the kidney. They can grow very large in size and are usually non-cancerous.
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Hepatic Fibrosis (Caroli Syndrome):
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Dysmorphic liver.
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Left lobe hypertrophy and right lobe atrophy.
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Enlarged and abnormal branching of hepatic arteries.
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Dilated splenic and portal veins.
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Scarred and atrophic kidneys with less than ten cysts (polycystic).
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What Are the Radiological Differential Diagnoses of Caroli Disease?
The differential diagnosis is as follows:
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Simple Cyst, Hydatid Cyst, or Polycystic Liver Disease (Autosomal Dominant)
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Cysts do not show any direct or indirect communication with the biliary system. The biliary tree is normal in such cases.
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Cysts have the appearance of clear fluid and not the same appearance as bile. Cysts are obscured in sequences like MRCP, ERCP, PTC (percutaneous transhepatic cholangiography), and hepatobiliary scintigraphy.
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Multiple Abscesses (Pyogenic or Amoebic)
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On ultrasound, these are seen as having thick walls with internal septation and debris.
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On CT or MRI, the thickened walls are also enhancing and accompanied by internal septation and debris.
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Frequently, there may be associated pleural effusion or atelectasis, which is not present in the case of Caroli’s disease.
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Choledochal Cyst
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By definition, as well as Todanis’s classification, choledochal cysts affect the extrahepatic biliary tree, except type IV a.
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There is also no associated renal disease in the case of choledochal cysts.
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Cystic or Necrotic Metastases
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On imaging, it shows enhancing mural nodules but not discrete dilated biliary channels.
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Rather, surrounding vessels and bile ducts may be distorted or disfigured by the malignant process.
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Primary Sclerosing Cholangitis
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It shows multiple alternating strictures and dilations involving both intrahepatic as well as extrahepatic biliary channels. This produces the characteristic beaded appearance on ultrasound, CT, or MRI.
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It is frequently associated with ulcerative colitis (70 percent) or other inflammatory bowel disease.
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Recurrent Pyogenic Cholangitis
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It also involves both intrahepatic as well as extrahepatic biliary channels.
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The stones that are formed have the characteristic of being cast-like and filling the ductal lumen (stones of Caroli’s disease do not fill the ductal lumen).
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Biliary Hamartoma
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Greater than 0.6 inches in diameter.
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No communication with the biliary tree.
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How Is Caroli Disease Treated?
The approach to treatment largely depends on the extent of involvement. Lobectomy or segmentectomy would suffice if the disease is confined within a lobe or segment. Patients having more diffuse involvement are candidates for liver transplantation. Until then, they may find some benefit in oral intake of bile salts and by biliary decompression, either by external drainage (percutaneous transhepatic biliary drainage) or internally by biliary-enteric anastomosis.
Conclusion
Caroli disease is a rare inherited disorder, and it is managed medically by an interprofessional team of doctors. The prognosis usually depends upon the extent of underlying medical or genetic abnormality and also the different organ systems involved. Therefore, to improve the prognosis outcome of this condition, timely surgical intervention may show long-term excellent outcomes.
