BLOG: A rare case of acinar cell cystadenoma in a 15 year-old adolescent

Natalie Cosgrove, MD, is a second year gastroenterology fellow at Thomas Jefferson University.  She completed her undergraduate training at Bucknell University. She graduated with a medical degree from Temple University and completed a residency in internal medicine at the University of Virginia.  She plans to pursue a career in academic advanced endoscopy.

Abstract

This report describes a rare pancreatic cystic lesion called an acinar cell cystadenoma (ACA) occurring in an adolescent male who presented with abdominal pain.  The cyst was initially identified on ultrasound and cross-sectional imaging. His diagnosis remained uncertain despite additional analysis including endoscopic ultrasound with fine needle aspiration.  The patient underwent successful laparoscopic excision for definitive diagnosis and management with an unremarkable postoperative course.  Although there are no formal recommendations for postoperative monitoring and his risk of recurrence is unknown, we recommended every other year MRI/ magnetic resonance cholangiopancreatography (MRCP) for postresection surveillance due to the theoretical risk of recurrence with malignant transformation.

Background

Incidental pancreatic cystic lesions are becoming increasingly common with more widespread use of cross-sectional imaging.  Pancreatic acinar cell cystadenocarcinoma and ACAs account for less than 5% of these lesions.  ACAs are rare pancreatic cysts that have been described in several case reports.  ACAs typically arise from a background of normal pancreatic parenchyma and may be focal or diffuse in distribution.  ACA may be unilocular or multilocular, with larger locules harboring internal septations.  Unilocular ACAs are predominantly lined by well-differentiated acinar epithelium without atypia and scattered ductal cells, while patches of ductal epithelium within a background of acinar epithelium are more typical of multilocular ACAs.

ACAs occur predominantly in females (61%-88% female), with the age of diagnosis ranging from 9 to 66 years and mean age of onset in the fourth decade.  Cysts may be incidental or symptomatic.  When symptomatic, the most common presentation is pain.  We describe a case of this rare cystic lesion occurring in a healthy adolescent male presenting with abdominal pain.

Case Report

A previously healthy 14-year-old male presented to an emergency room with 3 to 4 days of diarrhea and abdominal pain in November 2014.  Abdominal X-ray demonstrated dilated loops of bowel consistent with gastroenteritis.  His serum AST was slightly elevated at 65 units/L (ULN 37), however his remaining hepatic function panel, complete blood count, lipase and amylase were normal.  An abdominal ultrasound suggested a cystic structure medial to the left kidney with thickened internal septations.  Despite repeating the abdominal ultrasound in multiple planes, it remained unclear if the structure represented a distended fluid-filled loop of colon or a unique cystic lesion.  Subsequent computerized axial tomography (Figure 1) revealed a multiseptated cystic structure in the pancreatic tail measuring 3.5 x 4 x 5 cm with peripheral hyperdensities compatible with extrapancreatic calcifications.  Several of the cystic components demonstrated thickened walls with mild enhancement.  The pancreatic parenchyma and pancreatic duct appeared normal. No other pancreatic lesions were identified.  Multiple mildly dilated fluid-filled loops of large and small bowel with air-fluid levels compatible with gastroenteritis were also noted, which were felt to be the likely etiology of his symptoms.

 
Figure 1. Computer tomographic scan of abdomen.  Multiseptated cystic structure in the pancreatic tail (3.5 x 4 x 5 cm).

The patient’s symptoms resolved shortly following his emergency room visit, with normalization of his stools and resolution of his abdominal pain.  After careful review of his images, his pancreatic lesion was felt to represent a cystic pancreatic mass and less likely a pseudocyst or a solid pseudopapillary tumor with cystic components.  He was referred for an endoscopic ultrasound (EUS) to further characterize his lesion.  An EUS (Figure 2) performed December 2014 noted a 2.2 x 2.2-cm thick walled pancreatic tail lesion with a hypoechoic center and several adjacent anechoic lesions, the largest of which was 2.3 x 1.3 cm.  The pancreas otherwise appeared normal.  Fine needle aspiration of the largest anechoic lesion was performed using a 22g Expect needle (Boston Scientific).  One milliliter of pink tinged nonviscous fluid was aspirated.  Cyst fluid analysis revealed CEA 7.1 ng/mL and amylase 633 U/L.  Aspirate cytology was nondiagnostic with rare small groups of mildly atypical epithelial cells, benign acinar cells, ductal cells and fragments of fibrous tissue and debris.  RedPath PathFinderTG integrated diagnosis was also indeterminate, due to lack of polymerase chain reaction amplifiability from low DNA quantity and poor DNA quality.  

Figure 2. Endoscopic ultrasound image of a 2.3 x 1.3 cm anechoic lesion adjacent to the pancreatic tail.

The patient felt generally well and remained active in several sports, but continued to have episodes of recurrent abdominal pain.  Repeat contrast enhanced abdominal CT in July 2015 demonstrated a persistent pancreatic cystic lesion measuring  2.6 x 3.1 x 1.8 cm, with prior imaging not available for comparison at that time.  Although a definitive diagnosis had not been established, due to his recurrent pain and persistent lesion, the patient underwent laparoscopic excision in July 2015.  The patient tolerated the procedure well.  The lesion was easily dissected from the pancreas. Macroscopically, it was noted to have four cystic components, ranging in size from 0.8 x 0.7 x 0.4 cm to 2.6 x 1.6 x 1 cm.  Each cyst contained a white smooth wall filled with white, cloudy, watery fluid.  Microscopically, the cysts were lined by a single layer of cuboidal to columnar epithelium with focal acini, with one cyst demonstrating internal concretions (Figure 3).  No cytologic atypia or mitoses were present.  These features were consistent with a multilocular ACA.  

Figure 3. High powered magnification of cysts lined by a single epithelial layer of cuboidal to columnar epithelium with focal acini.

Discussion

We have described a case of a young adolescent male with a multilocular ACA who underwent successful cyst excision. To our knowledge, he is the second youngest patient to have been reported with this lesion. Additionally, while nearly all previously reported cases of ACA resulted in extensive pancreatic resections including pancreaticoduodenectomy, lateral pancreatectomy, and total pancreatectomy, we have described a case with successful cyst excision without pancreas resection.  Postoperatively, we have recommended every other year MRI/MRCP surveillance for this patient.  Whether or not this is warranted or beneficial, especially given this patient’s young age at diagnosis, is unclear.

It has been proposed that ACAs originate from non-neoplastic acinar dilatation that expand into and incorporate ducts and ductules, eventually forming large cystic lesions as secretions accumulate.  Ductal-to-acinar metaplasia has also been a theoretical explanation.  More recently, however, pancreatic ACA has been described as an adenoma.  While it has been suggested that this lesion is a precursor to acinar cell cystadenocarcinoma, the true malignant potential of this lesion remains unclear.  To our knowledge, no case report or case series  has reported evidence of malignant transformation of ACA with up to 7.8-year follow-up, regardless of whether or not the lesion was completely resected. 

Although ACAs lack atypia and mitotic activity which seem to favor a non-neoplastic lesion,  the discovery of multiple chromosomal gains on comparative genomic hybridization that contain a few cancer-associated genes and genomic instability suggest the lesion is preneoplastic.  Additionally, a case of ACA with low-grade dysplasia was recently reported.

We know from previous studies that ACA are likely to grow over time.  In a case series of 10 patients, 4 of whom underwent sequential imaging, all 4 cysts showed interval enlargement over time with a mean increase of 1.5 cm over 2.9 years.  No postoperative recurrences have been reported.  Until the course of ACA is better established, however, we believe these lesions should be aggressively monitored, with strong consideration for surgical resection to reduce the theoretical risk of malignant transformation.  Given the rarity of these cysts, future studies to support this will likely be limited.

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