Abdominal cystic lymphangioma

* Pancreatic lymphangiomas, which occur predominantly in women, are rare and account for only 1% of all lymphangiomas. The characteristic histologic features include multiple cysts lined by endothelial cells, irregularly distributed smooth muscle cells, and lymphoid aggregates in the wall of the cyst. We describe a 36-year-old woman with lymphangioma of the pancreas with "ovarian-like" mesenchymal stroma in the wall. This stroma, composed of uncommitted mesenchymal cells, has not been described previously in the wall of pancreatic lymphangiomas. Multiple small lymphatic channels that are found in this stroma recapitulate the development of lymphatic channels in the embryo. Lymphangioma of the pancreas may arise from distension of these lymphatic channels. Pancreatic lymphangioma may, therefore, be a developmental anomaly rather than a true neoplasm.

Lymphangiomas are uncommon benign neoplasms that are most often seen in the head, neck, and axilla. Intra-abdominal lymphangiomas, which are found in the mesentery, omentum, mesocolon, and retroperitoneum, form only 5% of all lymphangiomas.1 Pancreatic lymphangiomas occur predominantly in women, are exceedingly rare, and account for only 1% of all lymphangiomas.2 In the only histologic study of pancreatic lymphangiomas reported in the literature to date,3 the characteristic histologic features include multiple cystic spaces lined by flattened endothelial cells, irregularly distributed smooth muscle cells, and lymphoid aggregates in the walls of the cysts. In that study of 10 patients, an "ovarian-like" mesenchymal stroma was not described. Compagno and Oertel4 were the first to describe ovarian-like mesenchymal stroma in the wall of mucinous cysts of the pancreas. The presence of ovarian-like mesenchymal stroma in cystic lesions of the pancreas in women has raised many questions regarding the pathogenesis of these lesions. We report a case of pancreatic lymphangioma with ovarian-like mesenchymal stroma and propose a histogenesis for these unusual lesions.

REPORT OF A CASE

A 36-year-old woman presented to the hospital with complaints of abdominal pain of 4 months' duration. The pain was a dull, waxing and waning epigastric pain that radiated to the back, sometimes exacerbated by food. She reported a 9-kg (20-lb) weight loss. She underwent a laparoscopic cholecystectomy, but the abdominal pain continued. Computed tomography showed a cystic mass in the tail of the pancreas with mild thickening of the cyst wall (Figure 1). A distal pancreatectomy and splenectomy were performed.

PATHOLOGIC FINDINGS

Gross Findings

The specimen was a spleen and a portion of distal pancreas. The distal pancreas measured 8 x 5 x 1.5 cm. A unilocular cyst measuring 1.5 x 1.2 x 0.7 cm and containing serous fluid was found in the tail of the pancreas. The wall of the cyst was fibrous and measured 0.1 to 0.2 cm in thickness. The lining of the cyst was smooth with focal granularity. No other abnormalities were identified in the rest of the pancreas. The spleen weighed 195 g and was unremarkable.

Microscopic Findings

Although the lymphangioma appeared unilocular on gross examination, on microscopic examination it consisted of 1 large cyst and multiple smaller adjacent cysts lined by flat endothelial cells. A variably dense collagenous wall lined the cysts. Just beyond the collagenous wall, a densely cellular, ovarian-like spindle cell stroma of varying thickness was seen (Figure 2). Small and dilated lymphatic channels were also seen in the ovarian-like spindle cell stroma and in the adjacent pancreatic parenchyma (Figure 3). Scattered or small aggregates of lymphocytes were noted in the cyst wall. The pancreatic tissue adjacent to the cyst was atrophic. The rest of the pancreas was unremarkable. The lining cells did not stain with periodic acid-Schiff, with or without diastase pretreatment, or with mucicarmine stains.

Immunohistochemical studies were performed using formalin-fixed, paraffin-embedded tissue sections of the cyst wall. A standard avidin-biotin peroxidase complex technique was used in an automated immunostaining system (Ventana Medical Systems, Inc, Tucson, Ariz) with monoclonal antibodies directed against factor VIII-related antigen (Figure 4), CD31 and CD34, broad-spectrum cytokeratin, estrogen (Figure 5) and progesterone receptors (Figure 6), vimentin, smooth muscle actin, desmin, and HMB-45. The results of immunohistochemical staining are shown in the Table.

COMMENT

Pancreatic lymphangiomas occur predominantly in women, with a female-male ratio of approximately of 2:1. This tumor can be seen at any age, but the average age at presentation is 25.6 years. The clinical presentation is variable; abdominal pain, nausea, vomiting, and abdominal mass are the most common presenting symptoms, but these tumors may be silent and discovered as an incidental finding. On gross examination, the tumors are multi-cystic, typically ranging from 3 to 20 cm and affecting all regions of the pancreas.3 The lymphangioma described in this report appeared unilocular on gross examination. The reason for the discrepancy between the tumors described in the literature and the current tumor may be explained by the smaller size (1.5 x 1.2 cm) of the tumor we examined. On microscopic examination, however, multiple smaller cysts were noted adjacent to the larger cyst. A multiloculated cystic structure would have resulted with the enlargement of these smaller cysts. Flattened endothelial cells lining the cyst establish the diagnosis of lymphangioma. Demonstration of factor VIII-related antigen and CD31 in the lining cells confirms that the cysts are lined by endothelial cells.3 The wall of the cyst contains collagenous connective tissue, irregular fibers of smooth muscle, and few adipocytes and lymphocytes. As demonstrated in this case, the wall may also contain a dense ovarian-like mesenchymal stroma. Small lymphatic channels are found in this stroma and in the adjacent atrophic pancreatic tissue. Hemangioma of the pancreas, a rarely reported lesion, should be considered in the differential diagnosis, especially when there is significant hemorrhage. CD34 is focally and weakly expressed in endothelial cells of a lymphangioma, whereas it is strongly expressed in the endothelial cells of a hemangioma.5

The differential diagnosis of cystic pancreatic lesions includes both nonneoplastic and neoplastic lesions. Nonneoplastic cysts of the pancreas include pseudocyst, retention cyst of the pancreatic duct, mucinous nonneoplastic cyst of the pancreas, echinococcal cyst, and congenital cysts associated with von Hippel-Lindau disease and inherited polycystic kidney disease. Of these, the pseudocyst is the most common lesion, accounting for more than 75% of all pancreatic cysts. It is a unilocular cyst lined by fibrin and granulation tissue. The adjacent pancreatic tissue may show acute pancreatitis. Retention cysts of the pancreas are small cysts (

Neoplastic cystic lesions of the pancreas include mucinous cystic tumors, serous cystic tumors, acinar cell cyst-adenoma, and lymphoepithelial cyst. In general, histologic demonstration of an epithelial lining in these cystic tumors excludes a diagnosis of lymphangioma. Mucinous cystic neoplasm occurs predominantly in middle-aged women, with an average age at presentation of 44.5 years. It is a multiloculated cystic tumor in the pancreatic body and tail.9 The cyst is lined by columnar, mucin-producing epithelium with a ovarian-like mesenchymal stroma in the wall. More than half of a series of 130 patients with mutinous cystic tumor had epithelial stratification, complex papillary projections, and atypia. These tumors are considered cystadenocarcinoma with low malignant potential because of the cellular atypia of the lining cells and the tendency for tumor recurrence in patients who are treated by drainage alone.4,9

Serous cystic tumors are uncommon and classified into 2 groups: the serous microcystic adenoma and the oligocystic serous adenoma. The serous microcystic adenoma occurs predominantly in women with an average age at presentation of 66 years. On gross examination, it consists of a multicystic spongelike lesion arranged around a central scar. The cysts are lined by a single layer of cuboidal or flat epithelial cells with clear, glycogen-containing cytoplasm.10 The serous oligocystic adenoma has no sex predilection and is much less common than the microcystic adenoma. It is characterized by the presence of few but large cysts, lined by the same type of epithelium as the microcystic adenoma.6

Acinar cell cystadenoma is a recently described benign cystic pancreatic neoplasm affecting women predominantly, in which the lining cells demonstrate acinar differentiation. The tumors may be unilocular or multilocular.11 The lymphoepithelial cyst of the pancreas is reported predominantly in men, with an average age of 55 years at presentation. The average size of the lesion is 4.6 cm, and they may be unilocular or multilocular. The cyst is lined by stratified squamous epithelium and contains dense lymphoid tissue with lymphoid follicles in the wall.12

Lymphangiomas, regardless of their location, are all benign lesions, and it is not clear if they are neoplasms, hamartomas, or lymphangiectasias. However, most investigators regard lymphangiomas as malformations arising from sequestered lymphatic channels or acquired lesions due to obstruction caused by fibrosis of lymph channels. There are 2 theories regarding the development of lymphatic channels in the fetus. One theory favors formation of lymphatic channels from budding of endothelium-lined channels from the 5 fetal lymph sacs. In the second theory, the lymphatic channels start as spaces within primitive mesenchyme. The mesenchymal cells bordering these spaces form the endothelium. These spaces then coalesce to form long continuous lymphatic channels. The main lymphatic trunk then forms the thoracic duct.13 In the current case, several small lymphatic channels are present in the ovarian-like mesenchymal stroma. The ovarian-like mesenchymal stroma was at first thought to be ectopic ovarian tissue, but recent studies have shown that this stroma consists of uncommitted mesenchymal tissue cells and may therefore represent an embryonic mesenchymal rest.14 It is therefore not surprising to find small lymphatic channels in this primitive stroma. Distention of these sequestered lymphatic channels due to gradual accumulation of lymph leads to the formation of a lymphangioma. The reason for the female predominance of this lesion is not known. The presence of estrogen and progesterone receptors in the stromal cells may promote and maintain the mesenchymal stroma and may explain the development of this lesion in young women. The pancreatic lymphangioma should therefore be regarded as a developmental anomaly, occurring due to distension of sequestered lymphatic channels within primitive mesenchyme rather than a true neoplasm.

References

1. Galifer RB, Pous JG, Juskiewenski S, et al. Intraabdominal cystic lymphangiomas in childhood. Prog Pediatr Surg. 1978;11:173.

2. Daltrey IR, Johnson CD. Cystic lymphangioma of the pancreas. Postgrad Med J. 1996;72:564-566.

3. Paal E, Thompson LD, Hatfess CS. A clinicopathologic and immunohistochemical study of ten pancreatic lymphangiomas and a review of the literature. Cancer. 1998;82:2152-2157.

4. Compagno J, Oertel J. Mucinous cystic neoplasms of the pancreas with overt and latent malignancy (cystadenocarcinoma and cystadenoma): a clinicopathologic study of 41 cases. Am J Clin Pathol. 1978;69:573-580.

5. Ramani P, Shah A. Lymphangiomatosis: histologic and immunohistochemical analysis of four cases. Am J Surg Pathol. 1993;17:329-335.

6. Solcia E, Capella C, Kloppel G. Tumors of the Pancreas. Washington, DC: Armed Forces Institute of Pathology; 1997:37-39, 220-221. Atlas of Tumor Pathology, 3rd series, fascicle 20.

7. Kosmahl M, Egawa N, Schroder S, Carneiro F, Luttges J, Kloppel G. Mucinous nonneoplastic cyst of the pancreas: a novel nonneoplastic cystic change? Mod Pathol. 2002;15:154-158.

8. Yorganci K, Iret D, Sayek I. A case of primary hydatid disease of the pancreas simulating cystic neoplasm. Pancreas. 2000;21:104-105.

9. Thompson L, Robert B, Przygodzki R, Adair CF, Haffess C. Mucinous cystic neoplasm (mucinous cystadenocarcinoma of low-grade malignant potential) of the pancreas: a clinicopathologic study of 130 cases. Am J Surg Pathol. 1999;23: 1-16.

10. Compagno J, Oertel J. Microcystic adenomas of the pancreas (glycogenrich cystadenomas): a clinicopathologic study of 34 cases. Am J Clin Pathol. 1978; 69:289-298.

11. Zamboni G, Terris B, Scarpa A, et al. Acinar cell cystadenoma of the pancreas: a new entity? Am J Surg Pathol. 2002;26:698-704.

12. Adsay NV, Hasteh F, Cheng JD, et al. Lymphoepithelial cysts of the pancreas: a report of 12 cases and a review of the literature. Mod Pathol. 2002;15: 492-501.

13. Gray SW, Skandalakis JE. The lymphatic system. In: Embryology for Surgeons: The Embryological Basis for the Treatment of Congenital Defects. Philadelphia, Pa: WB Saunders Co; 1972:695-697.

14. Subramony C, Herrera GA, Turbat-Herrera E. Hepatobiliary cystadenoma: a study of five cases with reference to histogenesis. Arch Pathol Lab Med. 1993; 117:1036-1042.

Lizhen Gui, MD, PhD; Steven A. Bigler, MD; Charu Subramony, MD

Accepted for publication June 9, 2003.

From the Department of Pathology, University of Mississippi Medical Center, Jackson.

Reprints: Charu Subramony, MD, Department of Pathology, University of Mississippi Medical Center, 2500 N State St, Jackson, MS 39216-4505 (e-mail: csubramony@pathology.umsmed.edu).

Copyright College of American Pathologists Nov 2003
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