Pancreas

Acinar cell lesions

Acinar cystic transformation


Editorial Board Member: Xiaoyan Liao, M.D., Ph.D.
Deputy Editor-in-Chief: Aaron R. Huber, D.O.
Vidya Arole, M.D.
Wei Chen, M.D., Ph.D.

Last author update: 19 December 2023
Last staff update: 19 December 2023

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PubMed search: Acinar cystic transformation pancreas

Vidya Arole, M.D.
Wei Chen, M.D., Ph.D.
Page views in 2024 to date: 471
Cite this page: Arole V, Chen W. Acinar cystic transformation. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/pancreasacinarcellcystadenoma.html. Accessed March 19th, 2024.
Definition / general
  • Rare, nonneoplastic cystic lesion of the pancreas lined by benign appearing acinar and ductal epithelium
Essential features
  • First described in 2002; recognized by WHO in 2010 (Am J Surg Pathol 2002;26:698)
  • Clinically indolent; no cases of metastasis have been reported
  • Most cases found incidentally; though may be symptomatic
  • Cyst epithelium of acinar cystic transformation (ACT) consists of bland acinar and ductal epithelium, without mitoses, atypia and necrosis
Terminology
  • Other names include acinar cell transformation and acinar cell cystadenoma
ICD coding
  • ICD-11: DC30.0 - cyst of pancreas
Epidemiology
  • Rare; so far < 130 cases reported in the literature (J Clin Pathol 2023;76:740)
  • Female predominance (65.3%) with no age predilection
Sites
  • Found in all sites of the pancreas; can diffusely involve the gland
  • More common in head of pancreas
Pathophysiology
Etiology
  • Unknown; some may occur due to obstruction
  • No longer thought to represent the benign counterpart to acinar cell cystadenocarcinoma
Clinical features
  • Often found incidentally on imaging
  • Abdominal pain (42.1%), weight loss (4.9%), pancreatitis (4.9%), palpable mass (3.3%), jaundice (2.5%) (J Clin Pathol 2023;76:740)
Diagnosis
  • Requires clinical, radiologic and pathologic correlation
Radiology description
  • Nonspecific but the presence of 5 or more cysts, clustered peripheral small cysts, presence of cyst calcifications and absence of communication with the main pancreatic duct are supportive (Eur Radiol 2014;24:2128)
Prognostic factors
  • Clinically benign; there is no evidence of recurrence, malignant transformation or association with acinar cell carcinoma
  • Minority of cases involve controversial / high risk histomolecular features, including intralesional pancreatic intraepithelial neoplasia (PanIN) (4%), chromosomal gains and somatic mutations of KRAS and SMO genes (J Clin Pathol 2023;76:740)
Case reports
Treatment
  • Benign; no need of surgical resection (J Clin Pathol 2023;76:740)
  • Some are resected for symptomatic relief or to exclude other cystic neoplasms associated with malignancy
Gross description
Gross images

Contributed by Wei Chen, M.D., Ph.D.
Unilocular ACT

Unilocular ACT



Images hosted on other servers:
Multiple cystic lesions

Multiple cystic lesions

Raw specimen and fixed and cut specimen

Raw specimen
and fixed and
cut specimen

Microscopic (histologic) description
  • Cysts of variable sizes lined by bland flattened cuboidal acinar cells with apical granular eosinophilic cytoplasm and dense basophilic basal cytoplasm
  • Ductal epithelium can be admixed with the acinar cells
  • May contain corpora amylacea-like dense eosinophilic lamellar concretions
  • Multilocular cyst often demonstrates incomplete septa and club-like pseudopapillae
  • Low Ki67 proliferation (≤ 3%) and nuclear atypia is minimal
  • Cyst lining may show focal mucinous or clear cell change
  • Negative for ovarian type stroma, necrosis or infiltrative growth
  • References: J Clin Pathol 2023;76:740, Am J Surg Pathol 2023;47:379, Esposito: Pathology of the Pancreas, 1st Edition, 2022
Microscopic (histologic) images

Contributed by Vidya Arole, M.D. and Wei Chen, M.D., Ph.D.
Incidental microscopic ACT

Incidental microscopic ACT

Multilocular cystic structure

Multilocular cystic structure

Club-like pseudopapillae

Club-like pseudopapillae

Microscopic ACT CK19 immunostain

Microscopic ACT CK19 immunostain

Microscopic ACT trypsin immunostain

Microscopic ACT trypsin immunostain


Large unilocular ACT

Large unilocular ACT

ACT cyst epithelium

ACT cyst epithelium

Large ACT CK7 immunostain

Large ACT CK7 immunostain

Large ACT trypsin immunostain

Large ACT trypsin immunostain

Cytology description
  • Lesional epithelium indistinguishable from normal acinar and ductal cells
  • Smears usually low cellularity, containing cells resembling benign acinar or ductal epithelial cells
  • Smears / FNA specimens often interpreted as benign or nondiagnostic
  • Eosinophilic concretions can mimic mucinous secretions
Positive stains
Negative stains
Molecular / cytogenetics description
  • Single report of array comparative genomic hybridization (CGH) reported the following chromosome gains: 1p, 3p, 5q, 6p, 7q, 8, 10q, 11, 14, 20 and X (Am J Surg Pathol 2012;36:1579)
  • Random X chromosome inactivation observed in 5/5 cases, favoring nonneoplastic origin (Am J Surg Pathol 2013;37:1329)
  • In molecular analysis of 4 ACT cases, all cases had wild type status for KRAS and CTNNB1 genes (Oncol Lett 2014;8:852)
  • Next generation sequencing (NGS) performed on 9 ACT cases demonstrated driver mutations in 2 cases: one case a likely pathogenic mutation in SMO gene and the other a pathogenic mutation in KRAS gene (Am J Surg Pathol 2023;47:379)
Sample pathology report
  • Distal pancreas and spleen, distal pancreatectomy and splenectomy:
    • Acinar cystic transformation, 3.8 cm, pancreatic tail (see comment)
    • Proximal pancreatic resection margin is uninvolved
    • Benign spleen with no diagnostic abnormality
    • Comment: Sections show a multilocular cyst lined by bland cuboidal cells with granular cytoplasm. Eosinophilic concretions are present in the cyst. On immunohistochemical staining, the cyst epithelium is positive for both trypsin and CK19. The findings support the diagnosis of acinar cystic transformation.
Differential diagnosis
Board review style question #1

This is an incidental cyst found in the distal pancreas. On immunohistochemical staining, the cyst epithelium is positive for both CK19 and trypsin. Ki67 proliferation is low (< 3%). What is the diagnosis?

  1. Acinar cystic transformation
  2. Cystic acinar cell carcinoma
  3. Cystic solid pseudopapillary neoplasm
  4. Intraductal papillary mucinous neoplasm
Board review style answer #1
A. Acinar cystic transformation. The photograph demonstrates a cystic lesion lined by bland nonmucinous epithelium and filled with eosinophilic concretions. The positive CK19 and trypsin indicate ductal and acinar differentiation. The overall histomorphology and immunoprofile support the diagnosis of acinar cystic transformation of the pancreas. Answer D is incorrect because the cyst epithelium is nonmucinous. Answer B is incorrect because acinar cell carcinoma would have a much higher proliferation rate than 3%. Answer C is incorrect because solid pseudopapillary neoplasm should be negative for trypsin.

Comment Here

Reference: Acinar cystic transformation
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