Inflammatory pseudotumor of the spleen

Introduction
Inflammatory pseudotumor (IPT) is a lesion of unknown etiology that has been reported in numerous anatomic sites, including the spleen (7, 12, 13, 16, 18). By definition, the tumor is composed of a dominant spindle cell proliferation with a variable inflammatory component (5, 9, 15). Recent studies have demonstrated the spindle cells are myofibroblasts, prompting the currently preferred designation of inflammatory myofibro-blastic tumor (IMT) (5, 3, 15). Long considered a benign reactive proliferation, investigators have demonstrated the presence of chromosomal abnormalities and documented cases showing aggressive behavior (16, 20), supporting the theory that IMTs are true neoplasms.

Case report
A 23-year old male visited our hospital complaining of vague right upper quadrant pain. Physical examination was unremarkable and laboratory data ranged within normal limits including a leukocyte count of 8.000 /ml and an erythrocyte sedimentation rate (ESR) of 35 mm/h. Past history was significant only for a minor abdominal trauma occurring 10 years ago.
Sonography revealed a hypoechoic mass 2.5 cm in diameter located in the lower pole of a normal size spleen. Plain CT confirmed the presence of an iso-hypodense splenic mass. There was no evidence for invasion of surrounding structures or lymphadeno-pathy. Images obtained after i.v. contrast administration showed a mild to moderate homogeneous enhancement of the mass in a delayed phase. MRI of the upper abdomen utilizing a T1-weighted spin echo (SE) series (TR/TE=360 ms/ 20 ms) and a T2-weighted fast SE (FSE) series (TR/TE = 3200 ms/100 ms and TR/TE = 5400 ms/105 ms) demonstrated the splenic mass in greater detail. T1-weighted SE images showed an iso-intense mass while T2-weighted images showed a hypo-intense mass in comparison with the normal spleen. A central low intensity stellate area and a peripheral hypo-intense rim was better demonstrated on T2-weighted FSE images. Contrast enhanced T1-weighted images showed a mild to moderate hetero-geneous enhancement in the early phase and a more homogeneous enhancement of the mass in the delayed phase. No enhancement of the central stellate area and of the peripheral rim was noted.
The patient refused at first the recommended fine-needle aspiration biopsy and splenectomy and had a 30-month follow up. During this time there was a gradual increase in size of the mass reaching finally 7.8 cm in diameter. The last few months before surgery the patient suffered epigastric and left upper quadrant discomfort while laboratory investigation revealed an increased ESR (100 mm/h), leukocytosis (25.500 WBL/ml), microcytic hypochromic anemia (hemoglobin 8.5-9.5 G/dl) and a mild hypocalcemia. All tumor markers were negative. The imaging characteristics of the mass, except for its size, remained all the same. A CT-guided FNA was performed. Direct smears stained by May-Grünwald-Giemsa and cell block preparations stained by Hematoxyline-Eosin were analyzed. The smears contained a mixed cellular population. The most prominent cells were lymphocytes, immunoblasts and plasma cells (Fig. 1). The cell block preparations showed spindle or strap-shaped cells with elongated nuclei, surrounded by pale gray cytoplasm (Fig. 2). A few cells contained one or two bean-shaped nuclei with conspicuous nucleoli. Polymorphonuclear leukocytes and macrophages were abundant. The cytologic findings suggested a benign lesion, but there was a possibility of a malignant lymphoreticular neoplasm (i.e., dendritic cell tumor); malignant fibrous histiocytoma (inflammatory type) was also taken into consideration.
Splenectomy was finally performed and the patient was discharged on the 7th post-operative day in excellent condition. The spleen measured 13 cm X 13 cm X 6 cm and weighted 365 gr. The serosal surface was smooth. On cut sections a well-circumscribed firm, tan-gray tumor, was located at the lower pole of the organ with a maximum diameter 8 cm (Fig. 3). The specimen was fixed in 10% neutral-buffered formaldehyde, embedded in paraffin, cut at 5 µm, and stained with the conventional histological stains including hematoxylin and eosin, Giemsa, and periodic-acid Schiff (PAS). Additional studies for microorganisms were performed including Grocott methanamine silver, Brown-Brenn Gram, Brown-Hopps Gram, Ziehl-Neelsen, Warthin-Starry, and Fites stains.
Histologically the tumor was composed partly of spindle or strap-shaped cells, showing slight cellular and nuclear pleomorphism and partly of a mixed inflammatory infiltrate. The proportion of each of these elements varied but the spindle cell pattern was the dominant finding. The spindle cells were loosely arranged, or formed ill-defined fascicles, with a whorled or "featherlike" appearance. Focally, in the more cellular parts, these cells were tightly packed in well-defined, crossing fascicles and had abundant eosinophilic or amphophilic cytoplasm often extending to pointed ends. Some of the strap-shaped cells resembled rhabdomyoblasts, but cross-striations were not present. Mitotic figures were occasionally identified, but no atypical mitotic figures were present. The inflammatory cell component was composed of neutrophils, eosinophils, plasma cells, foamy histiocytes, and mature small lymphocytes. Occasional large lymphoid cells with vesicular nuclei and prominent nucleoli, consistent with immunoblasts, were identified. Collagenous stroma was identified in central areas of the tumor. The collagenous stroma resembled amyloid, but Congo red stain was negative. Foci of necrosis, hemorrhage, hemosiderin deposition, lymphoid follicles with reactive germinal centers or epithelioid granulomas, were not detected. The surrounding fibrous band which was separating the tumor from the remaining splenic parenchyma was composed of spindle cells, dense collagen, and small blood vessels.
Additional slides were stained with several monoclonal and polyclonal antibodies that are reactive in paraffin sections for immunohistochemical studies. An antigen-retrieval method using a pressure cooker was performed before immunohistochemical staining (17). The staining consisted of a first-stage incubation with the following primary monoclonal antibodies: CD79a (clone JCB117); CD20 (L26); CD15 (C3D1); CD21 (1F8); CD30 (BerH2); CD34 (QBEnd); anaplastic large cell lymphoma kinase (ALK-1); CD68 (PG-M1); smooth muscle actin, vimentin, desmin, S-100P, cytomegalovirus, and the latent membrane protein of Epstein-Barr virus (LMP-1). Polyclonal antibodies were used to test the expression of CD23 antigen and of the Ig chains k, l, m, g, d, and a. The antibodies were made visible with an indirect immunoperoxidase method for the antibodies for the heavy and light chains of the Ig molecule, whereas the alkaline phosphatase antialkaline phosphatase method was used to demonstrate the binding of the remaining antibodies (6). Antibodies were obtained from either DAKO (Glostrup, Denmark) or Novocastra (Newcastle-upon-Tyne, England). Standard positive and negative controls were used throughout.

Immunohistochemical profile
The spindle cells were most frequently immunoreactive for smooth muscle actin (Fig. 4) and vimentin. The immunohistochemical control for lymphoid markers showed a mixed B- and T-cell population. The plasma cells showed an equal mixture of kappa- and lambda- positive cells. Immunohistochemistry for cytomegalo-virus and Epstein-Barr virus were negative. CD68 (PG-M1) marked focally numerous histiocytes. CD34 highlighted the vascular pattern. CD15, CD30, and ALK-1 stains were negative. Special stains for myco-bacteria and fungi were negative.
Our findings established a diagnosis of inflammatory pseudotumor of the spleen.
Polymerase Chain Reaction (PCR)
DNA was extracted after dewaxing from 20-µm thick paraffin sections of both splenic samples (tumor and parenchyma) employing QIAEX (Qiagen, Hilden, Germany), according to the manufacturers' recommendations. A nested polymerase chain reaction (PCR) for rearrangements of Ig heavy chain gene and T-cell? receptor gene was performed as described previously (8). The results showed germline configuration of both T-cell receptor ? and immunoglobulin heavy chain genes.
Inflammatory pseudotumors are unusual lesions. They are recognizable from morphologic features as nonneoplastic lesions of uncertain origin and pathogenesis. The cellular composition can be remarkably hetero-geneous (9). In our case the smears revealed a plasmacellular population and transformed lymphocytes with an admixture of eosinophils and polymorphonuclear cells. Even though this background favored a mixed cellular type of Hodgkin's lymphoma, it was excluded since the search for diagnostic Reed-Sternberg cells did not produce results. Numerous mature and transformed lymphocytes and plasma cells militated against clonal lymphoid proliferation (2). The polyclonality of the lymphoid population was against non-Hodgkin's lymphoma. Although a fibroblastic proliferation was prominent and inflammatory cells abundant, storiform formations were absent. Mitotic activity was inconspicuous. Therefore, the inflammatory variant of malignant fibrous histiocytoma was excluded (21). On histologic grounds it is impossible to distinguish follicular dendritic cell tumors from inflammatory pseudotumors (4, 10, 11, 14, 19). These tumors share cytomorphologic features with myofibroblasts and histiocytes. They are characterized by CD21 and CD35 reactivity. Ultrastructural studies revealed characteristic elongated processes with complex interdigitation and desmosomal junctions. Furthermore, the association with EBV and dendritic tumors is suggested (1, 10). Since all EBV markers were negative, the possibility of dendritic cell tumor was excluded.
In our case one can assume that trauma played an initial role and that the presence of myofibroblasts, plasma cells, macrophages, and lymphocytes could represent a cell-mediated response.
Our patient recovered from the operation and is in excellent health.

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