Horseshoe kidney

* Primary carcinoid tumor, especially that arising in a mature teratoma of the kidney, is extremely rare; only 3 cases have been reported in the world literature to date. Because of the rarity of the lesion, its histogenesis and prognosis are unknown. We report a case of primary renal carcinoid tumor occurring in a mature teratoma in a 30-year-old woman. A computed tomographic scan of the abdomen revealed a mass in the left kidney containing dense calcification with minimal contrast enhancement. Histologically, the tumor was composed of trabecular and anastomosing ribbonlike nests, identical to the features of carcinoid tumors of other sites. Immunohistochemical stainings were positive for cytokeratin, neuron-specific enolase, and chromogranin. In addition, there were mature teratoid tissues, such as columnar epithelium, smooth muscle, and bone. The carcinoid tumor was under and closely apposed to the lining of the cysts. The patient did not have clinical manifestations of the carcinoid syndrome and had an uneventful recovery.

(Arch Pathol Lab Med. 2002;126:979-981)

Although carcinoid tumors are found most commonly in the gastrointestinal tract, they are also found in the respiratory, hepatobiliary, and genitourinary systems. A significant number of carcinoid tumors occurring in teratomas of the ovary have been reported.1 However, primary renal carcinoid tumors that are intimately associated with a teratoma are extremely rare. Since this association was first described by Kojiro et al2 in 1976, only 2 additional cases have appeared in the literature. Because of the rarity of this entity, we present a new case of a carcinoid tumor arising in a mature teratoma of the kidney.

REPORT OF A CASE

A 30-year-old woman presented with acute abdominal pain. She had microscopic hematuria and a body temperature of 38 deg C. Results of other laboratory studies were within normal limits. No symptoms related to carcinoid syndrome were reported. Radiographic study results of the chest were normal. Computed tomographic scan of the abdomen revealed a mass in the left kidney containing dense calcification with minimal contrast enhancement (Figure 1). No extension into the inferior vena cava and renal veins was detected. No other lesions were recognized in the gastrointestinal tract or elsewhere in the body. Angiographies revealed the mass to be hypovascular. The patient underwent left radical nephrectomy, and her postoperative course was uneventful. No serum or urine samples were obtained preoperatively for hormonal or polypeptide evaluation. Further investigations, including bone scanning, upper gastrointestinal endoscopy, colonoscopy, and urinary 5-hydroxyindoleacetic acid (5-- HIAA), were performed and results turned out to be normal. She remained asymptomatic 3 months postoperatively with normal abdominal findings on ultrasonography.

METHODS

Representative samples were fixed in 10%io neutral buffered formalin, dehydrated, and embedded in paraffin. Sections were stained with hematoxylin-eosin. Immunohistochemical studies were performed on deparaffinized sections using the avidin-biotin-peroxidase complex technique. The primary antibodies used were pan-cytokeratin (Immunotech, Marseille, France), polyclonal antibodies raised in rabbits against neuron-specific enolase (Signet Pathology Systems, Inc, Dedham, Mass), and a mouse monoclonal antibody against chromogranin (Signet Pathology Systems, Inc). Tissue sections that had been shown to be positive or negative were used as controls.

PATHOLOGIC FINDINGS

The tumor, present at the lower pole of the kidney, had a well-circumscribed, tan-pink, glistening, focally hemorrhagic, primarily solid appearance and measured 3.5 cm in maximum diameter (Figure 2, A). There was no infiltration into the surrounding perinephric fat. The renal artery, vein, and ureter were free of tumor. Microscopically, the tumor was composed of anastomosing ribbons intermixed with solid nests (Figure 2, B). Foci of rosettelike arrangements were present. The tumor cells were monotonous, small, polygonal epithelial cells, uniform in size with only slight variation in nuclear size and shape. The nuclei were round to oval and finely stippled with inconspicuous nucleoli. Focal areas of hemorrhage were identified. However, neither necrosis nor mitotic activity was appreciated. Immunohistochemical studies for cytokeratin, neuron-specific enolase, and chromogranin demonstrated diffuse strong cytoplasmic positivity (Figure 2, B). These findings are characteristic of a carcinoid tumor. Moreover, there were small cystic cavities filled with mucinous material and lined by a mucinous tall columnar epithelium (Figure 2, C). The cyst wall demonstrated foci of the carcinoid proliferation. Other teratomatous components included smooth muscle and bone (Figure 2, D). All elements were mature and well differentiated. These features are consistent with the diagnosis of a carcinoid tumor arising in a mature teratoma.

COMMENT

Carcinoid tumors of the kidney are rare, both in their pure form and as a component of teratoma; to date, only 31 cases have been reported in the literature.2-10 The most common presenting symptoms in these cases were abdominal pain and weight loss followed by gross hematuria. Carcinoid syndrome was infrequently reported. Most laboratory tests were noncontributory for diagnosis. The radiological features of these tumors were hypovascular or avascular on renal angiograms, hyperechoic on ultrasonography, and nonenhancing with low attenuation on bolus-enhanced computed tomography.8,9 No correlation has been established between the histologic patterns of the tumor and patient prognosis in the previously reported cases. However, the degree of cellular atypia and mitotic counts, if any, seem to correlate with patient outcome. Raslan et al6 described tumor stage at presentation to be an important prognostic factor. Minimal cellular atypia, lack of mitosis, and stage I cancer in our patient indicate a rather favorable prognosis.

Four of the previously reported renal carcinoid tumors occurred in horseshoe kidneys.3,8,10 The horseshoe kidney carries an increased risk of other renal neoplasms, such as Wilms tumor and renal pelvis cancer.10 Horseshoe kidneys have been proposed to be the result of teratogenic factors, which may also account for the increased risk of malignant tumors. Therefore, the presence of horseshoe kidney on radiographic evaluation should lead to careful investigation. Our patient had both kidneys in normal configuration.

A teratoma is an uncommon neoplasm containing a variety of cell types representative of more than 1 germ cell layer. Teratoma of the kidney is exceptionally infrequent.2 Most cases in which this diagnosis has been considered represent either retroperitoneal teratomas with renal extension or Wilms tumors with teratoid features. Carcinoids have rarely been reported to occur in association with teratomas; we identified a total of 3 cases in the medical literature.2,3,10 A summary of the reported cases is presented in the Table. All 3 of the previously described tumors occurred in men (age range, 23-65 years with a mean age of 42 years). The tumors ranged in size from 2 to 17 cm. Two patients had horseshoe kidneys. In the present case, intestinal epithelium-lined small cysts with smooth muscle and bone within the tumor may be taken as evidence of a preexisting teratoma from which the carcinoid tumor has arisen. Our patient therefore represents the fourth case of a renal carcinoid tumor in a teratoma. As in most of the reported cases, our patient did not have symptoms of a carcinoid syndrome.

The pathogenesis of renal carcinoid tumor is a matter of speculation. It has been proposed that neural crest tissue entrapped in the kidney during embryogenesis or renal pelvis cells undergoing intestinal metaplasia may be the origin of the primary renal carcinoid. Most authors believe the tumor derives from multipotential primitive stem cells capable of neuroendocrine differentiation.5-7,10 Carcinoid tumors occurring in ovarian and, less frequently, testicular teratomas are thought to derive from neuroendocrine cells of the gastrointestinal or respiratory epithelium, which are components of these lesions.1 The coexistence of renal abnormalities, mainly horseshoe kidneys and/or teratoma, strongly suggests that the development of this tumor may be related to predisposing embryological factors.

Owing to the rarity of these lesions, incomplete documentation of their clinicopathologic features, and lacking, inadequate, or short-term follow-up in many reports, the prognosis. and clinical behavior of these tumors remain unclear. Although primary renal carcinoid tumors appear to be more indolent than renal cell carcinomas, metastases to the regional lymph nodes, liver, kidneys, lungs, and bone have been described, often with a malignant course. Therefore, primary renal carcinoid tumors should be managed by radical nephrectomy and, when possible, retroperitoneal lymphadenectomy. When a renal carcinoid tumor is diagnosed, a search should be conducted for a possible primary elsewhere.

References

1. Sens M, Levenson TB, Metcalf JS. A case of metastatic carcinoid arising in an ovarian teratoma. Cancer. 1982;49:2541-2546.

2. Kojiro M, Ohishi H, Isobe H. Carcinoid tumor occurring in cystic teratoma of the kidney. Cancer. 1976;38:1636-1640.

3. Fetissof F, Benatre A, Dubois MP, Lanson Y, Arbeille-Brassart B, Jobard P. Carcinoid tumor occurring in a teratoid malformation of the kidney. Cancer. 1984;54:2305-2308.

4. Juma S, Nickel JC, Young I. Carcinoids of the kidney: case report and literature review. Can J Surg. 1989;32:384-386.

5. Unger PD, Russell A, Thung SN, Gordon RE. Primary renal carcinoid. Arch Pathol Lab Med. 1990;114:68-71.

6. Raslan WF, Ro JY, Ordonez NG, et al. Primary carcinoid of the kidney. Cancer. 1993;72:2660-2666.

7. Rudrick B, Nguyen G, Lakey WH. Carcinoid tumor of the renal pelvis: report of a case with positive urine cytology. Diagn Cytopathol. 1995;12:360-363.

8. Kurl S, Rytkonen H, Farin P, Ala-Opas M, Soimakallio S. A primary carcinoid tumor of the kidney: a case report and review of the literature. Abdom Imaging. 1996;21:464-467.

9. Sahin A, Demirbas M, Ozen H, et al. Primary carcinoid of the kidney. Scand J Urol Nephrol. 1996;30:325-327.

10. Lodding P, Hugosson J, Hansson G. Primary carcinoid tumor with ossification masquerading as calyx stone in a horseshoe kidney. Scand/ Urol Nephrol. 1997;31:575-578.

Jinyoung Yoo, MD, PhD; Sonya Park; Hee Jung Lee, MD; Seok Jin Kang, MD, PhD; Byung Kee Kim, MD, PhD

Accepted for publication October 31, 2001.

From the Department of Pathology, St Vincent's Hospital, Catholic University, South Korea.

Reprints: Seok Jin Kang, MD, PhD, Department of Pathology, St Vincent's Hospital, Catholic University, Suwon, Kyungkido, South Korea 442-723 (e-mail: sjkang@vincent.cuk.ac.kr).

Copyright College of American Pathologists Aug 2002
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