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Pseudopapillary solid cystic tumor arising from an extrapancreatic site.

Pseudopapillary solid cystic tumor (PSCT) is a distinctive tumor of the pancreas that usually occurs in adolescent girls and young women. (1-8) The tumor is histologically characterized by a combination of solid and pseudopapillary growth patterns of tumor cells with abundant pale-to-eosinophilic cytoplasm. Patients with this tumor have favorable prognoses after surgical resection. This type of tumor rarely arises in extrapancreatic sites, such as the retroperitoneum, mesocolon, and liver. (1,3,7,8) A case of PSCT arising in the omentum of a 46-year-old woman is presented with immunohistochemical, ultrastructural, and flow cytometric analyses because the tumor caused problems in diagnosis.

REPORT OF A CASE

A 46-year-old Japanese woman was incidentally noted to have an abdominal mass by an echogram during an annual examination. She had neither abdominal pain nor fever. Laboratory data showed no abnormalities. Laparotomy revealed a well-circumscribed, rubbery mass measuring 5.2 x 4.0 x 4.0 cm, which was located in the omentum and attached to the serosa of the gastric antrum and the second portion of the duodenum. The mass, which was not associated with the pancreas, was excised, and the pancreas showed no abnormality. Extensive systemic examination failed to find any other primary sites. No further therapy was administered. The patient was well without recurrence for the 3 months of follow-up.

PATHOLOGIC FINDINGS

Macroscopically, the excised abdominal lesion, measuring 5.2 x 4.0 x 4.0 cm, was a well-circumscribed, encapsulated, rubbery mass. On cut surface, it showed a yellowish to tan-brown solid tumor with a central uniloculated cyst that measuring 3.0 cm in greatest diameter and contained bloody serous fluid (Figure 1).

[FIGURE 1 OMITTED]

Microscopically, the tumor had a fibrous capsule. It showed a combination of solid and pseudopapillary growth patterns (Figure 2). In both patterns, the tumor cells were characterized by round-to-oval nuclei with fine chromatin and inconspicuous nucleoli and abundant pale-to-eosinophilic cytoplasm. The cytoplasm was negative for periodic acid-Schiff, Alcian blue, and Grimelius stains. Nuclear atypia was mild, and mitotic figures were rarely observed. The stroma was fibrous with hyalinization and vascular rich. Clusters of foamy histiocytes were scattered (Figure 2). Extensive samplings failed to find ectopic pancreatic tissue within or adjacent to the tumor.

[FIGURE 2 OMITTED]

Immunohistochemical and flow cytometric studies were performed using formalin-fixed, paraffin-embedded sections. The avidin-biotin-peroxidase complex technique and the peroxidase-antiperoxidase technique were used. The tumor cells were weakly and diffusely positive for vimentin (monoclonal, 1:100, Amersham, Little Chalfont, Buckinghamshire, UK). A total of 20% to 30% of tumor cells were positive for epithelial membrane antigen (monoclonal, 1:100, Dakopatts, Glostrup, Denmark) and [alpha]1-antichymotrypsin (polyclonal, 1:500, Dakopatts) (Figure 3). A few cells expressed cytokeratin, CAM 5.2 (monoclonal, 1:1, Becton Dickinson, Mountain View, Calif), and chromogranin A (polyclonal, 1:100, Incstar, Stillwater, Minn). The tumor cells were uniformly negative for desmin (polyclonal, 1:50, BioScience, Emmenbucke, Switzerland), [alpha]-smooth muscle actin (monoclonal, 1:100, Dakopatts), muscle actin, HHF-35 (monoclonal, 1:50, Enzo Biochemical, New York, NY), myoglobin (polyclonal, 1:800, Dakopatts), CD117 (c-kit, polyclonal, 1:50, Dakopatts), S100 protein (polyclonal, 1:100, Dakopatts), synaptophysin (polyclonal, 1:25, EuroDiagnostica, Apeldoom, Netherlands), [gamma]/-neuron-specific enolase (polyclonal, 1:150, Dakopatts), [alpha]-antitrypsin (polyclonal, 1:500, Dakopatts), CD68 (KP1, polyclonal, 1: 100, Dakopatts), HMB-45 (monoclonal, 1:50, Dakopatts), CD31 (monoclonal, 1:20, Dakopatts), and estrogen (monoclonal, 1:20, Novocastra, Burlingame, Calif) and progesterone receptors (monoclonal, 1:50, Novocastra). Appropriate positive and negative control experiments were also performed.

[FIGURE 3 OMITTED]

Formalin-fixed material was processed for electron microscopy. Ultrastructurally, the tumor cells had round nuclei with a narrow rim of marginated heterochromatin. The cytoplasm contained moderate amounts of mitochondria, rough endoplasmic reticulum, electron-dense granules of variable sizes, most likely representing lysosomes, and thin filaments (Figure 4). Poorly developed cell junctions were rarely observed.

[FIGURE 4 OMITTED]

Flow cytometric analysis indicated that the tumor was diploid, with 16% of S-phase fractions and 4.3% of the coefficients of variation.

COMMENT

The present tumor was macroscopically and microscopically similar to PSCTs of the pancreas. (1-8) It showed a solid and pseudopapillary growth pattern, and the tumor cells were characterized by round-to-oval nuclei and abundant pale-to-eosinophilic cytoplasm. The ultrastructural features were identical to those of previously reported cases. (6-8) Most conspicuous are tumor cells containing electron-dense granules of variable sizes (500 to 3000 nm), most likely representing lysosomes. (5,6) The immunohistochemical profiles in the present tumor were somewhat different from those of the reported cases. (6-8) Some tumor cells in the current case were positive for epithelial membrane antigen and [alpha]1-antichymotrypsin. This may be due to the differences of sensitivity and applied antibodies and immunohistochemical methods.

The differential diagnosis includes gastrointestinal stromal tumor, (9) paraganglioma, and newly described clear cell myomelanocytic tumor of the falciform ligament or ligamentum teres. (10) Gastrointestinal stromal tumor is histologically characterized by fascicular and/or epithelioid arrangements of spindle-to-oval cells and immunohistochemical expression of c-kit and CD34. It lacks pseudopapillary growth patterns. The present tumor was composed of round cells and was negative for c-kit and CD34. Paraganglioma is positive for neuroendocrine markers, such as synaptophysin and chromogranin A, and contains S100 protein-positive sustentacular cells. It lacks pseudopapillary proliferations and staining of vimentin and [alpha]1-antichymotrypsin. Clear cell myomelanocytic tumor of the falciform ligament or ligamentum teres, which is a perivascular epithelioid cell family of tumors, occurs in or immediately adjacent to the ligamentum teres and falciform ligament of children and young adults. The tumor consists of clear-to-faintly eosinophilic spindle cells arranged in fascicular and nest patterns. It expresses smooth muscle actin, myosin, and HMB-45. Although the present tumor histologically resembled a clear cell myomelanocytic tumor, the patient age, tumor site, and immunohistochemical features were different.

To the best of my knowledge, 8 extrapancreatic PSCTs have been reported, (1,3,7,8) a few cases in the retroperitoneum (1,3) and one each in the liver (8) and mesocolon. (7) Some of them were considered to arise from an ectopic pancreas. (1,7,8) There was no definitive evidence that the present tumor originated from an ectopic pancreas. Kosmahl et al (3) mentioned that the occurrence of a few PSCTs in the retroperitoneal space outside the pancreas can be related to the localization of the genital ridge during embryogenesis (1,3,7,8) and speculated that PSCTs might originate from genital ridge-related cells that were incorporated into the pancreas during organogenesis.

Reported flow cytometric studies of PSCTs showed that 17 of 21 cases were diploid and that the remaining 4 were aneuploid, 2 of which were malignant. (2,4) The present case was diploid with a high S-phase fraction. The prognostic significance of ploidy analysis of PSCTs remains unclear because of the paucity of the cases. Further studies are needed.

It is important to include PSCT, which shows epithelioid arrangements of tumor cells with clear-to-pale eosinophilic cytoplasm, in the differential diagnosis of omentary and mesenchymal tumors.

I thank Yokihiro Takeuchi, Naoko Yamada, Takashi Honma, Kuniko Kobayashi, Kazuya Sakurai, and Toshihisa Toda for their technical assistance and Michiko Takaki for her preparation of the photographs.

References

(1.) Kloppel G, Maurer R, Hofmann E, et al. Solid-cystic (papillary-cystic) tumours within and outside the pancreas in men: report of two patients. Virchows Arch A Pathol Anat. 1991 ;418:179-183.

(2.) Pettinato G, Manivel JC, Ravetto C, et al. Papillary cystic tumor of the pancreas: a clinicopathologic study of 20 cases with cytologic, immunohistochemical, ultrastructural, and flow cytometric observations, and a review of the literature. Am J Clin Pathol. 1992;98:478-488.

(3.) Kosmahl M, Seada LS, Janig U, Harms D, Kloppel G. Solid-pseudopapillary tumor of the pancreas: its origin revised. Virchows Arch. 2000;436:473-480.

(4.) Nishihara K, Nagoshi M, Tsuneyoshi M, Yamaguchi K, Hayashi I. Papillary cystic tumors of the pancreas: assessment of their malignant potential. Cancer. 1993;37:82-92.

(5.) Klimstra DS, Wenig BM, Heffess CS. Solid-pseudopapillary tumor of the pancreas: a typical cystic carcinoma of low malignant potential. Semin Diagn Pathol. 2000:17:66-80.

(6.) Solecia E, Capella C, Kloppel G. Tumors of the Pancreas. Washington, DC: Armed Forces Institute of Pathology; 1997:120-144. Atlas of Tumor Pathology; 3rd series, fascicle 20.

(7.) Ishikawa O, Ishiguro S, Ohhigashi H, et al. Solid and papillary neoplasm arising from an ectopic pancreas in the mesocolon. Am J Gastroenterol. 1990; 85:597-601.

(8.) Kim YI, Kim ST, Lee GK, Choi BI. Papillary cystic tumor of the liver: a case report with ultrastructural observation. Cancer. 1990;65:2740-2746.

(9.) Kindblom LG, Remotti HE, Aldenborg F, Meis-Kindblom JM. Gastrointestinal pacemaker cell tumor (GISPCT): gastrointestinal stroma tumors show phenotypic characteristics of the intestinal cells of Cajal. Am J Pathol. 1998;152:1259-1269.

(10.) Folpe AL, Goodman ZD, Ishak KG, et al. Clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres: a novel member of the perivascular epithelioid clear cell family of tumors with a predilection for children and young adults. Am J Surg Pathol. 2000;24:1239-1246.

Accepted for publication April 17, 2001.

From the Department of Pathology, The Jikei University School of Medicine, Tokyo, Japan

Reprints: Masaharu Fukunaga, MD, Department of Pathology, The Jikei Daisan Hospital, 4-11-1, Izumihoncho, Komaeshi, Tokyo, 201-8601, Japan (e-mail: maasafu@jikei.ac.jp).
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Author:Fukunaga, Masaharu
Publication:Archives of Pathology & Laboratory Medicine
Geographic Code:1USA
Date:Oct 1, 2001
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