Section 4 -

FNAB of Bone and soft tissue tumors: Case presentations Ayoub Nahal Adel Assaf

Introduction: In multidisciplinary tumor centers, bone lesions can be diagnosed - even subclassified - with high accuracy by combining information from radiographic images and cytology preparation interpreted by bone radiologists and cytopathologists possessing expertise in musculoskeletal tumors [1, 2, 4]. To further enhance the diagnostic accuracy, specimen adequacy must be highly respected and the material be considered optimal only if the cytologic findings correlate with the clinicopathologic/radiographic picture. Because of the simplicity, low morbidity, and economical benefits, FNAB is recommended as a first step in the diagnosis of a bone lesion. Likewise, FNAB of soft tissue tumors in the hands of experienced cytopathologists – and more so with on-site adequacy assessment - in conjunction with ancillary techniques can obtain high levels of accuracy in diagnosing benign versus malignant tumors [4]. Subtyping, however, remains more difficult especially in the spindle and myxoid categories, but some authors have considered it not only possible but reliable as well with good correlation with final histology [3]. The role of MR imaging in the diagnosis of bone and soft tisuue tumors has become extremely important in the past ten years. Patient age, radiographic appearance, and clinical history remain essential for accurate diagnosis. However, early detection of lesions and preoperative characterization of benign and malignant tumors with MRI is a useful practice. MR imaging is superior to bone scintigraphy in detection of marrow lesions. Tumors of bone, marrow infiltration and myeloproliferative disorders replace normal bone marrow resulting in focal or diffuse decrease in signal intensity on T1-weighted pulse sequences. MRI can sometimes provide the exact diagnosis in certain soft tissue masses such as hemangioma or lipoma. However, its prime role is and should remain as the principal modality used in the staging of musculoskeletal neoplasms. If local excision is being considered, the exact margin of the tumor may be assessed accurately with MR imaging, hence helping in limb salvage in cases of malignant lesions. T2-weighted sequences provide high contrast between the lesion and the surrounding muscle. The most sensitive technique however, combines IV gadolinium enhancement with fat suppression. Case 1: Aneurysmal Bone Cyst(ABC) Aneurysmal bone cyst is a benign bone lesion composed of blood filled spaces separated by variably cellular connective tissue septa containing fibroblasts, osteoclast-type giant cells and reactive woven bone. In up to 50% of lesions, an underlying bone tumor can be identified, typically a Giant cell tumor of bone, Chondroblastoma, Fibrous Dysplasia, or other benign entities. Less commonly, ABC can be seen in malignant bone tumors. Recent molecular studies have determined a recurrent translocation t(16;17) in primary ABC while lacking in secondary ABC [5]. This suggests that despite its morphological similarity with primary ABC, secondary ABC represents a nonspecific morphologic pattern occurring in many bone tumors. Radiographically, it presents as a multiloculated, lytic, metaphyseal-centered dilation of the bone, well circumscribed with a sclerotic rim and occasional periosteal new bone formation. The presence of fluid-fluid levels is a helpful feature. Fine needle aspiration biopsy generally yields scant material with a few stromal fragments of benign fibroblasts and reactive myofibroblasts, pigmented histiocytes, and osteoclast-type giant cells in a bloody background. The giant cells are sparse and relatively small with fewer nuclei than the ones seen in Giant cell tumor of bone. Since many secondary ABC's mask an underlying bone tumor, the cytology interpretation should be placed in the context of the radiographic presentation and a definite diagnosis of primary versus secondary ABC deferred to the final curetted specimen. Case 2: Myxoid Liposarcoma FNAB specimens of myxoid liposarcoma can vary in cellularity depending on the amount of the myxoid stroma and whether a round cell component is present. In the absence of a round cell component, the predominant finding is the presence of small fragments of myxoid matrix rich with arborizing thin wall capillaries [6]. The neoplastic cells are seen within and outside the myxoid stroma. They have uniform round small nuclei with dark chromatin and inconspicuous nucleoli. The diagnostic univacuolated lipoblasts are rarely seen [7]. Round cell liposarcoma yields specimens more cellular than typical myxoid liposarcoma, and are composed of significantly larger population of round cells with hyperchromatic nuclei and conspicuous nucleoli. Typically, they are discohesive with many single cells scattered in the background. The amount of myxoid stroma in round cell liposarcoma is related to the percentage of the round cell component within the tumor. When the round cells predominate, minimal stroma may be detected. Low grade myxoid liposarcomas can be distinguished from other myxoid neoplasms by their complex network of thin capillaries and their uniform round nuclei that display mild cytoatypia. At the opposite end, high grade round cell liposarcomas are easily diagnosed as malignant and can be distinguished from other malignant round cell neoplasms by their uniform large round nuclei with large nucleoli and relatively fine chromatin. Necrotic debris and cell karyorrhexis is usually not seen. Helpful clues to the diagnosis reside in the identification of lipoblasts and myxoid stroma. Determining the amount of round cell component in a myxoid liposarcoma (and therefore the grade) on FNA is very difficult [8] as this requires the documentation of 5>% round cells in a given tumor. This assessment can only be reliable in large representative tissue sections. Case 3: Well Differentiated Liposarcoma, inflammatory type The diagnosis of atypical lipomatous tumors and well differentiated liposarcomas are not easily established by FNAB, particularly in the absence of a cell block. The diagnostic lipoblasts and the atypical stromal cells are rarely present on the smears, a typical reflection to their minor contribution in the diagnostic architecture appreciated on tissue biopsy. Therefore, if atypical cells are seen, FNA of a mature appearing tumor may suggest a liposarcoma. However, in the absence of atypia, an atypical lipomatous tumor/well differentiated liposarcoma can not be usually excluded. A core or open biopsy then should be performed, if clinically indicated. A cytologic diagnosis can become even more difficult in the sclerosing and inflammatory variants. In the sclerosing variant, aspiration may yield scant cells due to the firm fibrosing nature of the tumor. In the inflammatory variant, lymphocytes may predominate and mask the scattered atypical stromal cells causing a misdiagnosis with a lymphoid process. The role of immunohistochemistry in the diagnosis of well differentiated liposarcoma was limited before the advent of the commercially available MDM2 and CDK4, the 2 oncogenes expressed specifically in the atypical nuclei of ALT/WDLS [9]. These stains are reliable and can be used in cell blocks. Their positive expression favors a liposarcoma. Atypical stromal cells can also be seen in pleomorphic lipomas. Often, these are small superficial lesions in the head and neck region of the elderly and most likely not aspirated. If immunohistochemistry is feasible, these atypical stromal cells are usually positive for CD34 [10] and negative for MDM2 and CDK4 [9]. Case 4: Low Grade Fibromyxoid Sarcoma (LGFMS) Although the histologic features of low grade fibromyxoid sarcoma are well established, there are less than handful individual case reports in the literature describing the cytologic features of this tumor by fine-needle aspiration. In all these reported cases, the final diagnosis was rendered on histologic grounds and the cytologic features studied in context of the final diagnosis [11]. The recognition of this lesion is important because of its indolent but metastasizing nature. The aspirate is relatively cellular with a myxoid background; the neoplastic cells are distributed singly with complete loss of cohesion and show no discernible cytoplasm. They overlap with a feathery appearance. The nuclei are oval, angulated to spindle shaped with minimal pleomorphism, dark chromatin and absent nucleoli. No capillaries are usually identified. The differential diagnosis of mildly atypical spindle cell proliferation includes among many, schwannoma, deep fibromatosis, synovial sarcoma and low grade myxofibrosarcoma. The cells of LGFMS can be distinguished from the characteristic myofibroblasts of Desmoid tumor, the wavy nuclei of Schwannoma that are arranged in clusters, the elongated and more atypical and pleomorphic cells of myxofibrosarcoma, and the more cohesive nature of the neoplastic fragments of synovial sarcoma. Even if more common spindle cell neoplasms are excluded, due to the striking subtle cytoatypia, a definitive diagnosis based on FNAB alone may be difficult; however, correlating the cytologic and clinical findings can narrow the range of diagnosis. In the presence of a cell block, histologic architecture may be the only additional clue since no specific immunohistochemical marker expression is known yet to exist. Case 5: Nodular Fasciitis Nodular fasciitis is a reactive myofibroblastic lesion with rapid growth occurring in a short time frame. In the early proliferative phase, the lesion is cellular and accompanied by a variably myxoid stroma. In the late regressive phase, the stroma is mature and fibrous and the cellularity diminished. In both ends of the spectrum, the lesional cell is an activated myofibroblast that is reliably recognized by its long spindle tapered shape, round vesicular nucleus with fine chromatin and conspicuous single nucleolus. The cytoplasm is often abundant and basophilic. FNAB of nodular fasciitis in a proliferative phase yields cellular smears of discohesive clusters to individual spindle myofibroblasts resembling a tissue culture pattern [14]. Myxoid background can be appreciated more so in Diff-Quick preparation and occasional osteoclast-type giant cells are commonly seen. A lymphoplasmacytic infiltrate is also a common feature. These cytologic features are characteristic of nodular fasciitis. Therefore, FNAB in the right clinical context is diagnostic, and the lesion should be managed nonsurgically first, with close clinical follow-up. If regression does not occur within four to eight weeks, surgery should then be performed [12, 13]. Case 6: Extraskeletal Ewing's Sarcoma Small round cell malignant tumors (SRCMT) in adults comprise a heterogeneous group of neoplasms that share a common morphologic appearance but treated with divergent therapeutic agents. Based on cytomorphology alone, a specific diagnosis is extremely difficult to render with certainty. The advances in immunohistochemistry and molecular biology have facilitated the diagnosis not only in large tumor samples but also in small cytologic preparations. In adult soft tissue tumors, the differential diagnosis of SRCMT includes with decreasing frequency: Lymphoma, Extraskeletal Ewing's/PNET, Round cell liposarcoma, Alveolar Rhabdomyosarcoma, Mesenchymal Chondrosarcoma, Desmoplastic round cell tumor, and poorly differentiated form of Synovial sarcoma. In bone, Small cell variant of Osteogenic sarcoma, Ewing's sarcoma, and lymphoma are among the most common possibilities. The finding of SMRCT of bone, as in cytologic findings of any bone tumor, needs to be strongly correlated with the imaging studies. Osteoid matrix production favors osteogenic sarcoma over lymphoma and Ewing's. While the same advises apply to SMRCT in soft tissue, the radiographic information is often less characteristic. On FNAB, Ewing's Sarcoma can be easily established if sufficient material is obtained for ancillary studies. The smears are markedly cellular and composed of mostly individually dispersed cells with possible clustering that is usually due to hypercellularity. A necrotic background accompanied by a high karyorrhectic debris is the exception rather than the rule. The tumor cells are generally uniform with monomorphic round nuclei and fine evenly distributed chromatin and inconspicuous nucleoli. Nuclear membranes are smooth and the nuclear cytoplasmic ratio is extremely high [16]. Cytoplasmic vacuoles and Homer Wright rosettes are rarely appreciated, but when present are highly suggestive [18]. While typical Ewing's sarcoma shows little variation among tumor cells, it exists several atypical variants where larger cell size, prominent nucleoli, mild pleomorphism and slight spindling can be accepted [15]. These features differ from usual large cell lymphomas which tend to show more complex nuclear membranes, vesicular to coarse chromatin with small nucleoli. The background is almost always necrotic. Lymphoglandular bodies are commonly seen, and their presence is always indicative of lymphoid malignancies [19]. Cytogenetics and immunohistochemistry performed on cell blocks - if the material permits - can help confirming the diagnosis of Ewing's Sarcoma. Over 90% of Ewing's sarcomas express CD99 (O13), and 70-90% express Fli-1. The Cautious interpretation of the two latter stains is advised as CD99 is known to lack specificity and Fli-1 sensitivity. Neuroendocrine and neuroectodermal markers (S100, CD57, Synaptophysin and NSE) are variably expressed when neuroectodermal differentiation is present and their inclusion in the immunopanel can be of significant help. Molecular confirmation of the fusion transcripts EWS/FLI-1, ERG can further confirm the diagnosis and can be performed either by FISH of PCR. References Introduction: Soderland V, et al: Combined radiology and cytology in the diagnosis of bone lesions: a retrospective study of 370 cases. Acta Orthop Scand 2004 Aug;75(4):492-9. Jorda M, et al: Fine-needle aspiration cytology of bone: accuracy and pitfalls of cytodiagnosis. Cancer 2000 Feb 25;90(1):47-54. Palmer HF, et al: Subgrouping and grading of soft-tissue sarcomas by fine-needle aspiration cytology: a histopathologic correlation study. Diagn Cytopathol 2001 May;24(5):307-16. Singh HK, et al: Fine needle aspiration biopsy of soft tissue sarcomas: utility and diagnostic challenges. Adv Anat Pathol. 2004 Jan;11(1):24-37. Case 1: Aneurysmal Bone Cyst Oliveira AM, Perez-Atayde AR, Inwards CY, Medeiros F, Derr V, Hsi BL et al. USP6 and CDH11 oncogenes identify the neoplastic cell in primary aneurysmal bone cysts and are absent in so-called secondary aneurysmal bone cysts. Am J Pathol 2004; 165(5):1773-1780. Case 2: Myxoid Liposarcoma: Kilpatrick SE, et al: The value of fine-needle aspiration biopsy in the differential diagnosis of adult myxoid sarcoma. Cancer 2000 Jun 25;90(3):167-77. Layfield LJ: Logistic regression analysis of myxoid sarcomas: a cytologic study. Diagn Cytopathol 1998 Nov;19(5):355-60. Palmer HF, et al: Subgrouping and grading of soft-tissue sarcomas by fine-needle aspiration cytology: a histopathologic correlation study. Diagn Cytopathol 2001 May;24(5):307-16. Case 3: Well Differentiated Liposarcoma Binh MB: MDM2 and CDK4 immunostainings are useful adjuncts in diagnosing well-differentiated and dedifferentiated liposarcoma subtypes: a comparative analysis of 559 soft tissue neoplasms with genetic data. Am J Surg Pathol 2005 Oct;29(10):1340-7. Suster S: Immunoreactivity for the human hematopoietic progenitor cell antigen (CD34) in lipomatous tumors. Am J Surg Pathol. 1997 Feb;21(2):195-200. 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