Giant Pelvic Solitary Fibrous Tumor Obstructing Intestinal and Urinary Tract: A Case Report and Literature Review

By Yi, Bing Bewtra, Chandra; Yussef, K; Silva, Edibaldo

We are reporting a giant pelvic neoplasm, a rare solitary fibrous tumor that presented with a large bowel obstruction and bilateral ureteral obstruction because of its size and location. Preoperative diagnosis required complex pathological studies to exclude a high- grade sarcoma suspected clinically. Complete resection was required for resolution of obstructive symptoms. Prognosis for solitary fibrous tumors is usually good after complete resection. Recurrence and metastasis may be related to rare aggressive histological features, including nuclear atypia, hypercellularity, greater than four mitoses/10 high power fields, and necrosis. Because histology is not always a reliable predictor of prognosis, careful long-term follow-up is necessary for this tumor. Solitary fibrous tumors (SFTs) are rare spindle cell neoplasms most likely arising from mesenchymal cells. SFTs were originally described in the pleura, the most common site for this tumor; however, extrathoracic SFTs are seemingly diagnosed with increased frequency. We report a case of a giant pelvic SFT that required complicated clinical management. Case Report

A 65-year-old man with an 80-pack per year smoking history presented with significant urinary retention and intermittent diarrhea alternating with constipation, early satiety, and a 30- pound weight loss. Physical examination was unremarkable except for fullness of the lower abdomen. Abdominal CT showed a giant pelvic mass measuring 17 x 13 cm that completely occupied the pelvis (Fig. 1). Interestingly, a single horseshoe kidney was found with significant bilateral hydronephrosis. The urinary bladder was nearly completely displaced out of the pelvis, as the Foley catheter balloon could be identified in the extrapelvic left lower abdomen. Metastatic work-up revealed no distant metastases. CT-guided core- needle biopsy rendered a preliminary diagnosis of a low-grade sarcoma. This suggested a very limited potential for response to chemotherapy or radiation as preoperative maneuvers to shrink this bulky tumor. Similarly, an angiogram was performed to look for large feeding vessels to embolize in an attempt to shrink the tumor or diminish the potential hemorrhagic complications at surgery. Unfortunately, no significant feeding vessels or perforators were found.

The patient’s obstructive symptoms worsened and he was explored to divert his fecal stream. At exploration, the tumor was found to fill the pelvis completely. Thus, a loop ileostomy and subsequent percutaneous nephrostomies were performed for urinary obstruction. This staged approach allowed time to improve the patient’s nutrition and pulmonary status. The patient was re-explored 5 months later and the tumor, which was firmly adherent to the pelvic side walls and vasculature, was resected en bloc, sparing his midline horseshoe kidney. His postoperative course was unremarkable, and his nephrostomy tubes and loop ileostomy were reversed several months later. The patient is doing well, with no evidence of recurrent tumor or obstructive symptoms in over 1 year.

Pathology

The 17-cm mass appeared well encapsulated. The cut surface was firm and white, with an area of hemorrhage from the preoperative biopsy (Fig. 2, left). Microscopic examination showed monomorphic spindle-shaped fibroblasts with no significant nuclear atypia or pleomorphism. The mitotic count was 2 per 10 high power field (HPF; Fig. 2, right). Multiple immunoperoxidase stains showed tumor cell positivity with vimentin, CD-34, CD-99, and bcl-2. Other markers for muscle, epithelial, or neural differentiation were all negative, including desmin, SM, s-100, myoglobin, melan A, factor XIII, S-IOO A6, and pan cytokeratin. Low (1%-2%) proliferation marker (Ki-67) positivity inferred the low-grade nature of the tumor. Ultrastructural examination of the lesion showed fibroblast-type cells in a dense collagenous background. Notably, the cells showed no microvilli, melanosomes, or neurosecretory granules (picture not shown). These ultrastructural findings are consistent with solitary fibrous tumor. As noted, cytogenetic studies were attempted but were not possible because no metaphases were seen in cultures established from the specimen, although cellular proliferation was identified.

FIG. 1. Giant pelvic tumor completely occupied the true pelvis. The bladder is displaced to left lower quadrant (Foley in the bladder).

Discussion

Extrathoracic solitary fibrous tumors (SFTs) have been recognized in almost all body sites, although most frequently in the head and neck.1 The histogenesis of SFTs has been debated for years, and current immunohistochemical and ultrastructural studies strongly point to a mesenchymal origin, maybe fibroblast.2 Pathologically, SFTs are characterized by unique microscopic, immunohistochemical, and ultrastructural findings.

FIG. 2. Left, Cut section of gross specimen; right, Light microscopy (hetnatoxylin and eosin section, 400 x ; see “Case Report” description for details).

Microscopic examination shows spindle cells dispersed among elongated dense collagen fibers in a “patternless” pattern3 or a great variability of growth pattern.4 Foci of short fascicular or storiform arrangement of the spindled cells are typically seen. The nuclei are usually bland and mitoses are rare (<1-2 mitoses per 10 HPFs) in the average case.2,3 Atypia, hypercellularity, necrosis characters are also described, but are not always consistent to prognosis.

As noted, this “patternless pattern” of SFTs may mimic many other tumors, including synovial sarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumor, dedifferentiated liposarcoma, dermatofibrosarcoma protuberans, gastrointestinal stromal sarcoma, hemangiopericytoma, desmoplastic mesothelioma, spindle cell thymoma, and spindle cell carcinoma.5 Therefore, immunohistochemical studies play an important role in the differential diagnosis. CD34, a vascular endothelial marker,1,6 and more recently, bcl-2,7, 8 have been found to be the only marker consistently positive in this tumor, although marked diminution or complete loss of CD34 expression has been shown in high-grade foci of recurrent tumor.9 It has been proposed that CD34 and bcl-2 can be used together with typical microscopic findings in the diagnosis of SFTs.10 In addition, SFTs always express vimentin, which is the marker of mesenchymal cells such as fibroblasts. Pancytokeratin is used to rule out epithelial origin, and desmin is used to rule out muscle cells. S-100 and melan A are markers of melanoma, which are normally negative in SFTs.

Ultrastructural features in these tumors suggest a myofibroblastic/fibroblastic nature. The tumor consists of polygonal to spindle fibroblastic cells encompassed by abundant collagen fibrils. The neoplastic cells have spindle or oval euchromatic nuclei with irregular contours. The relatively scant cytoplasm contains inconspicuous but focally dilated or branching rough endoplasmic reticulum and prominent Golgi apparatus. In cellular clusters, the slender interdigitating cytoplasmic processes are joined by occasional rudimentary cell junctions. Some tumor cells may display myofibroblastic differentiation characterized by cytoplasmic microfilaments with focal densities and pinocytotic vesicles at the periphery and minimal basal lamina surrounding the neoplastic cells. Tumor cells do not show any microvilli, cell junctions, melanosomes, or neurosecretory granules, thus ruling out other potential tumors, befitting the clinical presentation.

The clinical presentation is often caused by the compression of adjacent organs and tissues. Most lesions remain asymptomatic and are only picked up as an incidental finding on radiologie examinations. The syndrome of hypoglycemia is seen in less than 5 per cent of cases (the so-called Doege-Potter syndrome), and the associated tumors are large with a high mitotic rate. The cause of hypoglycemia is related to the insulin-like growth factors produced by these tumors.11 Complete local excision is the treatment of choice, and this is curative in most cases. Chemotherapy or radiation therapy may be options for recurrent, metastatic, or nonresectable tumors.12 Although most SFTs have benign histologie features, nuclear atypia, hypercellularity, greater than four mitoses/10 HPFs, and necrosis may be seen in up to 10 per cent of extrathoracic SFTs, and are associated with aggressive clinical behavior.5 However, the histology is not always predictive of clinical behavior. Some tumors with benign cytomorphology do recur,5,9 whereas some tumors with cellular atypia and increased mitotic activity (>4/10 HPF) may follow a benign course.9,13 Therefore, careful long-term follow-up is recommended for all patients with solitary fibrous tumors.

In short, a giant solitary fibrous tumor with aggressive clinical features (obstructive bowel and urinary tract symptoms) was found to be resectable with clear margins despite preoperative imaging suggestive of the contrary. Characteristic pathologic features confirmed the preoperative diagnosis. Complete resection with curative intent was performed, but long-term follow-up is required. This report serves as a reminder that SFTs should be included in the differential diagnosis of well-circumscribed large spindle cell tumors in the pelvis. REFERENCES

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BING YI, M.D.,* CHANDRA BEWTRA, M.D.,[dagger] K. YUSSEF, M.D,[double dagger] EDIBALDO SILVA, M.D., PH.D.*

From the Departments of * Surgery, [dagger] Pathology, and [double dagger] Radiology, Creighton University Medical Center,

Omaha, Nebraska

Address correspondence and reprint requests to Edibaldo Suva, M.D., Associate Professor of Surgery, Creighton University Medical Center, 601 North 30th Street, Omaha, NE 68131.

Copyright Southeastern Surgical Congress May 2007

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