Clinical History

A 38-year-old female with a history of hypertension presented to the emergency department with complaints of nausea, vomiting, and back pain. MRI showed a T1 hypointense, T2 hyperintense, nonenchancing cystic lesion at the tail of the pancreas, which caused mass effect upon the spleen and stomach. A distal pancreatectomy was subsequently performed. The patient is currently being followed with no evidence of recurrence or malignant transformation.

Macroscopic Description
Grossly, there was a well-circumscribed 11.5 x 10 x 3.7 cm cyst at the tail of the pancreas containing cloudy, milky fluid (Figure 1). The lining of the cyst was smooth, without papillary projections or solid areas. There was no communication between the cyst and the main pancreatic duct.

Figure-1. Gross photograph of the cystic lesion at the tail of the pancreas

 Histologic/Cytologic Features 
Microscopic pictures of the cyst wall are shown in Figures 2 – 4. Sections show a unilocular cyst lined by 1-2 cell layers of bland cuboidal epithelium with abundant eosinophilic granular apical cytoplasm and basally oriented nuclei consistent with acinar differentiation. There was  little intervening ductal differentiation (mucin-containing ductal epithelium). No substantial nuclear atypia or mitotic activity was present. The cyst was surrounded by a thick fibrous pseudocapsule, which was composed of dense collagen with scattered fibroblasts. No ovarian type stroma was identified.

Figure-2. H&E stain low power view of the cyst wall
Figure-3. H&E stain median power view of the cyst wall
Figure-4. H&E stain high power view of the cyst wall
 


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Answer: Acinar cystic transformation of the pancreas


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Final diagnosis:  

Acinar cystic transformation of the pancreas

Educational Objectives and Discussion:

Educational Objectives

  1. To understand the clinicopathologic features of the acinar cystic transformation of the pancreas.
  2. To understand the molecular alterations of the acinar cystic transformation of the pancreas.
  3. To discuss the differential diagnoses of the acinar cystic transformation of the pancreas.

Discussion

Acinar cystic transformation of the pancreas, also called acinar cell cystadenoma, is currently considered a non-neoplastic cystic pancreatic lesion that is lined by benign-appearing acinar and ductal epithelium. These lesions can occur throughout the pancreas, but they are more common in the pancreatic head. Some examples may diffusely involve the entire organ. Acinar cystic transformation commonly occurs in adults (mean age 43 years old) and shows female predominance (F:M=3:1) (1-9). Clinically it can present as recognized macroscopic lesions or incidental microscopic lesions. Patients can present with abdominal pain, dyspepsia or palpable mass. Some cases are completely asymptomatic. The etiology is unknown, but some cases may be related to obstruction. The size of these lesions can range from 1.5 cm – 19.7 cm (mean 5.8 cm) and cysts may be unilocular or multilocular with a smooth cyst lining and rare communication with the main pancreatic duct.

Microscopically, acinar cystic transformation is characterized by cysts of variable sizes lined by bland cuboidal eosinophilic epithelium with both acinar and ductal differentiation, cytoplasmic zymogen rich granules and without significant nuclear atypia, mitotic figures, necrosis, or infiltrative growth pattern.

The apical zymogen granules stain positively for the periodic acid-Schiff (PAS) stain and are resistant to diastase (Figures 5 & 6). Immunohistochemical labeling for the pancreatic enzymes trypsin (Figure 7), chymotrypsin, and lipase is seen in the lining epithelial cells, and cytokeratins (such as cytokeratin 7) are also detectable in the lining epithelium.

Molecular studies have been done on a few cases with one showing chromosomal gains of 1p, 3p, 5q, 6p, 7q, 8, 10q, 11, 14, 20, and X by array comparative genomic hybridization (10). However, another study performed X-chromosome inactivation analysis on 5 cases and showed that these lesions have a random X-chromosome inactivation pattern (11), supporting a non-neoplastic process.

Figure-5. PAS stain of the cyst wall
Figure-6. PAS-D stain of the cyst wall
Figure-7. Immunohistochemical stain for trypsin

Differential diagnosis:

Serous cystadenoma of the pancreas is a benign epithelial cystic neoplasm that is composed of uniform cuboidal, glycogen-rich pale pink to clear cells that often form cysts containing serous fluid. Immediately underlying the clear epithelium is an interweaving network of capillaries that is challenging to see on H&E but can be highlighted by CD31 stain. A central scar can be present, which consists of hyalinized stroma. Owing to the presence of abundant intracytoplasmic glycogen, PAS staining is positive in tumor cells but PAS-D staining is negative. Serous epithelium is immunoreactive for inhibin and Glut-1.

Mucinous cystic neoplasm (MCN) is another differential that is also characterized by pancreatic cysts of the body/tail that do not communicate with pancreatic duct. Cysts are characteristically lined by mucinous/non-mucinous epithelium with underlying entity defining ovarian-type stroma. Acinar epithelial lining is not a feature of MCN.

Squamoid cysts of the pancreatic duct are not neoplastic and are lined by epithelium with squamous or transitional differentiation instead of acinar and ductal differentiation.

Acinar cell cystadenocarcinoma is exceedingly rare. The epithelium of acinar cell cystadenocarcinoma is more complex than that of acinar cystic transformation and the acinar cells are less well polarized, and show significant nuclear atypia, including pleomorphism and prominent nucleoli. Areas of necrosis, solid nests of neoplastic cells, easily identifiable mitoses, and infiltration into the surrounding stroma support a malignant diagnosis.


References:

1. Zamboni G, Terris B, Scarpa A, et al. Acinar Cell Cystadenoma of
the Pancreas: A New Entity? Am J Surg Pathol. 2002, 26(6): 698-704.
2. Albores-Saavedra J. Acinar Cystadenoma of the Pancreas: A
Previously Undescribed Tumor. Ann Diagn Pathol. 2002, 6(2): 113-5.
3. Chatelain D, Paye F, Mourra N, et al. Unilocular Acinar Cell
Cystadenoma of the Pancreas an Unusual Acinar Cell Tumor. Am J Clin
Pathol. 2002, 118(2): 211-4.
4. G Klöppel. Pseudocysts and Other Non-Neoplastic Cysts of the
Pancreas. Semin Diagn Pathol. 2000 Feb; 17(1); 7-15.
5. McEvoy MP, Rich B, Klimstra D, et al. Acinar Cell Cystadenoma of
the Pancreas in a 9-year-old Boy. J Pediatr Surg. 2010, 45(5): e7-9.
6. Wolf AM , Shirley LA, Winter JM, et al. Acinar Cell Cystadenoma of
the Pancreas: Report of Three Cases and Literature Review. J
Gastrointest Surg. 2013l,17(7): 1322-6.
7. Singhi AD, Norwood S, Liu TC, et al. Acinar Cell Cystadenoma of the
Pancreas: A Benign Neoplasm or Non-Neoplastic Ballooning of Acinar and
Ductal Epithelium. Am J Surg Pathol. 2013, 37(9): 1329-35.
8. Wang G, Ji L, Qu FZ, et al. Acinar Cell Cystadenoma of the
Pancreas: A Retrospective Analysis of Ten-Year Experience From a
Single Academic Institution. Pancreatology, 2016, 16(4): 625-31.
9. Zhang X, Zhu H, Yang X, et al. Post-obstructive Cyst Formation in
Pancreas and Cystic Acinar Transformation: Are They Same? Pathol Res
Pract 2017, 213(8): 997-1001.
10. Khor TS, Badizadegan K, Ferrone C, et al. Acinar cystadenoma of
the pancreas: a clinicopathologic study of 10 cases including
multilocular lesions with mural nodules. Am J Surg Pathol.
2012;36(11):1579‐1591.
11. Singhi AD, Norwood S, Liu TC, et al. Acinar cell cystadenoma of
the pancreas: a benign neoplasm or non-neoplastic ballooning of acinar
and ductal epithelium? Am J Surg Pathol. 2013;37(9):1329‐1335.


 

Case contributed by:

Yue Xue, MD, PhD

Rebecca C. Obeng, MD, PhD

Department of Pathology and Laboratory Medicine

Northwestern University, Chicago, IL 60611, USA

Conflict of Interest: NO

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