Pancreatic cystosis

Pancreatic cystosis is a rare abdominal manifestation of cystic fibrosis characterized by the presence of multiple epithelium-lined macroscopic cysts that replace the pancreatic parenchyma in patients with cystic fibrosis. It is typically an asymptomatic incidental imaging diagnosis and the cysts are generally considered benign. Management is typically conservative, except when symptomatic or in rare cases of mass effect on adjacent structures.

Epidemiology

The condition typically develops in cystic fibrosis patients in the second decade of life ¹. It has been estimated that pancreatic macrocysts are incidentally present in 8% of children and young adults with cystic fibrosis, while in 3% the pancreatic parenchyma is completely replaced by macrocysts ². Prevalence in adults with cystic fibrosis is not well established ^ref.

Diagnosis

The diagnosis is typically made on the basis of a known diagnosis of cystic fibrosis, and the presence of multiple pancreatic macrocysts (defined as >1 cm in diameter), following the exclusion of other possible causes of the cystic transformation of the pancreas (see Differential diagnosis below) ^ref.

Confirmatory biopsy is considered unnecessary in patients with cystic fibrosis ^ref.

Clinical presentation

Many patients are asymptomatic, while cystosis can be described in patients with multiple gastrointestinal symptoms including abdominal discomfort, nausea, fullness and poor quality of life ³. Given the prevalence of these symptoms in patients with cystic fibrosis, the contribution of pancreatic cystosis to an individual patient’s symptoms can be difficult to ascertain.

Pathology

Pancreatic macrocysts are true cysts, lined by an epithelial layer. Defective transmembrane ion transport results in hyper-concentrated or inspissated pancreatic secretions. This increases intraluminal pressure in the pancreatic ducts, resulting in ductal ectasia and eventual formation of cysts of various sizes ⁴.

Radiographic features

Macrocysts are typically distributed throughout the gland and are of various sizes. They are >1 cm in size by definition, and parenchymal cystic replacement with cysts up to 12 cm have been reported ^1,3,5. In many cases, there is complete replacement of the pancreatic parenchyma.

Cross-sectional imaging can be useful in cases of very large cysts to assess for mass effect on adjacent viscera and vascular structures.

Ultrasound

• sharply-circumscribed hypoechoic structures, often with posterior acoustic enhancement

• no mural nodules or solid foci

• typically uniloculated, but some may be multiloculated

• may be separated by hyperechoic pancreatic parenchyma; in some cases the parenchyma may be completely replaced by macrocysts ²

CT

• well-defined homogenous lesions with thin, smooth walls

• the majority are isodense (<20 HU) or slightly hyperdense relative to water (20-33 HU)

• no mural calcifications

MRI

Macrocysts typically follow water signal on all sequences, except in atypical cases of hemorrhage or high internal protein content ⁶.

Signal characteristics

• T1

  • homogenous low signal intensity

  • high signal only if hemorrhage or high protein content

• T2

  • homogenous high signal, similar to CSF

  • fluid-fluid level if hemorrhage

  • MRCP often does not demonstrate communication with the pancreatic duct ^[6], and the pancreatic duct may be of normal caliber in young patients ^[2]

• T1 C+ (Gd): does not enhance following administration of gadolinium

Treatment and prognosis

To date, no case has been reported of malignant transformation of a cystic fibrosis-related pancreatic macrocyst ^1,2,6. As such, management is generally conservative, except in cases of persistent symptoms attributable to the cysts. These include chronic abdominal pain, obstructive gastrointestinal symptoms and poor quality of life related to the cysts ³.

For the uncommon cysts causing mass effect, management may be endoscopic (including cystogastrostomy) or surgical, where the treatment is partial or total pancreatectomy ⁴.

Differential diagnosis

In the absence of a known history of cystic fibrosis, the radiological differential diagnosis includes other causes of cystic transformation and enlargement of the pancreas ^ref:

• pancreatic pseudocyst

  • suggested by a history of pancreatitis or trauma

  • typically fewer cysts

• polycystic kidney disease (PCKD)

  • pancreatic cystic transformation differs pathologically from CF-related cystosis in that the main pancreatic ducts form multilocular cavities, with the acini remaining intact

  • distinction is made on clinical history

  • kidneys will appear abnormal

  • radiologically these entities can be otherwise indistinguishable

• von Hippel Lindau disease: similar to PCKD above, diagnosis is suggested by clinical history and abnormal appearance of the kidneys

• serous cystadenoma

  • demographic is typically elderly women

  • may have T2 hypointense central fibrous scar, and fibrous septa may enhance on post-contrast T1-weighted MRI

• mucinous cystic neoplasm

  • middle-aged women

  • cysts are often more heterogenous and may have septations; cysts may have higher T1 signal due to presence of mucin

• pancreatic lymphangioma

  • lobulated and multiseptated

  • cysts may show hemorrhage