Pathologic quiz case: a mass of the spleen. (Residents' Pages).
[FIGURE 1 OMITTED]
The spleen was submitted for intraoperative pathologic evaluation. It weighed 245 g and contained a well-circumscribed, centrally necrotic, tan, fleshy mass that measured 7 x 6 x 6 cm (Figure 2). Frozen section of the mass showed a spindle cell neoplasm with no obvious features of malignancy. Permanent sections demonstrated that the splenic architecture was entirely effaced by the' lesion. A fibrous capsule of varying thickness separated the mass from the adjacent spleen. The histology varied from zones of spindle cells with angulated nuclei, vesicular chromatin, and a single conspicuous nucleolus (Figures 3 and 4), admixed with plasma cells, lymphocytes, neutrophils, and eosinophils, to areas of dense sclerosis and collagen accumulation. There were prominent deposits of hemosiderin- and lipid-laden macrophages. The central area of the tumor was completely necrotic and consisted of amorphous eosinophilic material. No Reed-Sternberg cells, acid-fast organisms, fungi, parasites, or foreign material were identified, and mitoses were sparse. Flow cytometry did not reveal a monoclonal population. Ultrastructurally, the tumor consisted of plasma cells, lymphocytes, histiocytes., and fibroblasts with abundant collagen. Immunohistochemical stains documented that the spindle cells were positive for vimentin, weakly positive for smooth muscle actin, and negative for cytokeratin and desmin. Immunophenotyping showed a mixed lymphoid population of T and B cells, while plasma cells expressed both [kappa] and [lambda] light chains. The uterus contained leiomyomata, and the fallopian tubes and ovaries were unremarkable.
[FIGURES 2-4 OMITTED]
What is your diagnosis?
Pathologic Diagnosis: Inflammatory Myofibroblastic Tumor of the Spleen
Inflammatory myofibroblastic tumor (IMT) is a benign lesion composed primarily of proliferating myofibroblastic spindle cells admixed with inflammatory cells. While initially recognized in the lung, this tumor has been described in virtually all major organs. Many synonyms, such as plasma cell granuloma, inflammatory pseudotumor, and inflammatory myofibroblastoma, have been used to describe this rare entity. (1)
Cotelingam and Jaffe (2) described the first patient with IMT in the spleen, and since then only 43 additional patients with IMT have been described in the literature. Inflammatory myofibroblastic tumor in the spleen is usually an incidental finding, although it may present as a mass. Weight loss, malaise, anemia, or thrombocytopenia may be rare presenting features. (3) Most commonly, IMT occurs in adults, although a 5-year-old boy has been affected. (4)
As seen in the patient described here, IMT may have a spectrum of histologic findings. The most common feature is spindle cell proliferation admixed with inflammatory cells, mostly plasma cells and lymphocytes. A zonal distribution with central necrosis, foamy histiocytes, granulomas, and giant cells is quite characteristic. In general, the most common microscopic pattern of IMT is a myxoid/vascular pattern, although compact spindle cells and a hypocellular fibrous pattern are seen also, depending on the stage of development of the tumor.
The concept of IMT has evolved together with the history of the myofibroblast. Myofibroblasts are the basic cellular elements of tissue repair, as well as the cell of origin of various benign and malignant neoplasms with apparent myofibroblastic differentiation. Included in this latter group are nodular fasciitis, fibromatoses, angiomyofibroblastoma, sarcomas with a prominent myofibroblastic component, and malignant fibrous histiocytoma. (1) So far, it is generally agreed that the myofibroblast is a ubiquitous cell that is present in a variety of tissues and organs. When tissue is injured, fibroblasts undergo transformation and become a "hybrid" cell with features of the fibroblast and the smooth muscle cell.
The pathogenesis of the IMT remains unclear. Griffin et al (5) found a clonal chromosomal aberration of chromosome 2p23 in 2 IMTs. Su et al (6) provided more evidence supporting the clonal origin of this tumor. The most recent work by Lawrence et al (7) confirmed the clonal origin, reporting that activation of the ALK-receptor tyrosine-kinase locus region is a recurrent oncogenic event in IMT. Epstein-Barr virus was detected by in situ hybridization in 60% of cases of IMT of the spleen. The role of increased interleukin-6 secreted by plasma cells and myofibroblastic proliferation similar to that seen in Castleman disease should be considered. (8)
Radiologically, IMT may mimic a malignant tumor with a differential diagnosis of lymphoma, metastatic carcinoma, or splenic hamartoma. (9) The pathohistologic differential diagnosis includes monoclonal hematopoietic neoplasms, such as large cell lymphoma, Hodgkin lymphoma, and plasmacytoma. Those neoplasms are ruled out by the lack of monoclonality in the mononuclear cells of IMT. Spindle cell neoplasms, such as malignant fibrous histiocytoma, are included in the differential diagnosis as well. The large atypical polygonal cells with prominent nucleoli and brisk mitotic activity should, however, differentiate between the two. Benign lesions, such as granulomas, are excluded by routine histology and stains for acid-fast bacilli or fungi.
Follicular dendritic cell tumor is an extremely rare malignant neoplasm with a microscopic' appearance similar to that of IMT, but few cases have been described in the spleen. (10) Unlike the IMT, a follicular dendritic cell tumor is rarely positive for smooth muscle actin, but does show positivity for CD21 and CD35. Severe cytologic atypia and frequent mitoses are present also.
In conclusion, IMT is a rare neoplasm of the spleen in which the preoperative clinical and morphologic diagnosis is difficult, especially in patients with symptoms of a malignancy, such as weight loss, anemia, and thrombocytopenia, or deep venous thrombosis as in the patient described. The behavior of these tumors in the spleen is that of a benign neoplasm, and no recurrences or metastatic disease has been found after splenectomy. Fine-needle aspiration is not specific and carries a high risk of bleeding. Intraoperative frozen section is recommended for the differentiation of IMT from primary and metastatic neoplasms. Final diagnosis requires a detailed morphologic examination and additional immunohistochemical stains. The lesion, although benign and rare, is important because it may have clinical and pathologic features similar to several malignancies.
(1.) Coffin CM, Dehner LP, Meis-Kindblom JM. Inflammatory myofibroblastic tumor, inflammatory fibrosarcoma and related lesions: an historical review with differential diagnostic considerations. Semin Diagn Pathol. 1998;15:102-110.
(2.) Cotelingam JD, Jaffe ES. Inflammatory pseudotumor of the spleen. Am J Surg Pathol. 1984;8:375-380.
(3.) Thomas RM, Jaffe ES, Zarate-Osorno A, Medeiros LJ. Inflammatory pseudotumor of the spleen: a clinicopathologic and immunophenotypic study of eight cases. Arch Pathol Lab Med. 1993;117:921-926.
(4.) Aru GM, Abramowsky CR, Ricketts RR. Inflammatory pseudotumor of the spleen in a young child. Pediatr Surg Int. 1997;12:299-301.
(5.) Griffin CA, Hawkins AL, Dvorak C, et al. Recurrent involvement of 2p23 in inflammatory myofibroblastic tumors. Cancer Res. 1999;59:2776-2780.
(6.) Su LD, Atayde-Perez A, Sheldom S, et al. Inflammatory myofibroblastic tumor: cytogenetic evidence supporting clonal origin. Mod Pathol. 1998;11:364-368.
(7.) Lawrence B, Perez-Atayde A, Hibbard MK, et al. TPM3-ALK and TPM4-ALK oncogenesis in inflammatory myofibroblastic tumors. Am J Pathol. 2000;157: 377-384.
(8.) Arber DA, Weiss LM, Chang KL. Detection of Epstein-Barr virus in inflammatory pseudotumor. Semin Diagn Pathol. 1998;15:155-160.
(9.) Hayasaka K, Soeda S, Hirayama M, et al. Pseudotumor of the spleen: US and MRI findings. Radiat Med. 1998;16:47-50.
(10.) Perez-Ordones B, Rosai J. Follicular dendritic cell tumor: review of the entity. Semin Diagn Pathol. 1998;15:144-154.
Accepted for publication April 5, 2001.
From the Departments of Pathology and Laboratory Medicine (Drs Mosunjac and Majmudar) and Surgery (Dr Feliciano), Emory University, Grady Memorial Hospital, Atlanta, Ga.
Reprints not available from the authors.
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|Title Annotation:||inflammatory myofibroblastic tumor of the spleen|
|Author:||Mosunjac, Marina B.; Feliciano, David V.; Majmudar, Bhagirath|
|Publication:||Archives of Pathology & Laboratory Medicine|
|Date:||Dec 1, 2001|
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