Cyto-histological correlations in primary, recurrent, and metastatic bone and soft tissue osteosarcoma. Institut Curie's experience.

To determine diagnostic cytomorphologic features of osteosarcoma on fine-needle aspiration materials, we reviewed the cytologic material and corresponding histologic slides of 126 tumors in 107 patients. Fifty-five (43.6%) tumors were primary, 31 (24.6%) were recurrent, and 40 (31.8%) were metastatic. Review of original cytology reports revealed that 120 (95.3%) tumors were diagnosed as malignant. Six (4.7%) cases were reported as suspicious, false-negative, or unsatisfactory samples. Our findings showed that osteoblastic roundish cells, spindle-shaped cells, reactive giant cells, and osteoid were the most consistent features representative of osteosarcoma. Periosteal reactions, fractures with callous formation, giant cells of osteoclastic type in various conditions, chondrosarcoma with enchondral ossification are entities to consider in the differential diagnosis.

Cyto-histological correlations in primary, recurrent and metastatic rhabdomyosarcoma: the institut Curie's experience.

To determine diagnostic cytomorphologic features of rhabdomyosarcoma (RMS) on fine-needle aspiration (FNA) material, the cytologic material and corresponding histologic slides of 180 tumors obtained from 109 patients were reviewed. Fifty eight (32.2%) tumors were primary, 34 (18.9%) recurrent, and 88 (48.9%) metastatic. A review of original cytology reports revealed that 176 of 180 (97.8%) tumors were either diagnosed accurately or as round cell sarcoma, while 3 (1.7%) were reported as suspicious. In one case (0.5%), the material was unsatisfactory. No false negative samples were seen. When FNA morphology was correlated with different histological subtypes, the alveolar subtype RMSs were more cellular than the nonalveolar ones (91.4% vs. 64.9%). Similarly, alveolar subtype RMSs compared with nonalveolar ones exhibited more rhabdomyoblastic cells (77.1% vs. 52.7%), alveolar structures (67.6% vs. 10.8%), giant, multinucleated cells (22.9% vs. 6.7%), mitotic figures (57.1% vs. 18.9%), and cyto-nuclear atypia (77.1% vs. 43.2%). Inversely, spindle-shaped cells were more frequently seen in nonalveolar versus alveolar RMSs (37.8% vs. 20.9%).

Cytohistologic correlations in schwannomas (neurilemmomas), including "ancient," cellular, and epithelioid variants.

Schwannoma accounts for one of the most common benign mesenchymal neoplasms of soft tissues. Although it is well defined in the cytology literature, particular histologic subtypes such as "ancient," cellular and epithelioid variants could be a source of diagnostic difficulties. We have reviewed cytology aspirates and corresponding histologic sections from 34 schwannomas diagnosed at Institut Curie. Histologically, 24 cases were classic, 5 were "ancient," 4 were cellular, and 1 was epithelioid schwannomas. No example of melanotic schwannoma was recorded. Original cytologic diagnosis was schwannoma in 13 (38.2%) cases, benign soft tissue tumor in 11 (32.4%), pleomorphic adenoma in 2 (6%) cases, angioma in 1 (2.9%) case, nodular fasciitis in 1 (2.9%) case, suspicious in 3 (8.8%) cases, and not satisfactory in 3 (8.8%) cases. There were no major differences between classical, "ancient," cellular, and epithelioid variants on cytology smears. Myxoid stroma, mast cells, and intranuclear inclusions were limited to classical subtype. Similarly, cyto-nuclear atypia was more frequent in classical subtype than in other subtypes. Schwannoma should be differentiated from well-differentiated malignant peripheral nerve sheath tumor, neurofibroma, and pleomorphic adenoma, in the last instance particularly for head and neck lesions.

[Low grade fibromyxoid sarcoma: a clinico-pathologic analysis of 7 cases]. / Sarcome fibromyxoïde de bas grade: une étude clinico-pathologique de 7 cas.

OBJECTIVES: Low-grade fibromyxoid sarcoma (LGFMS) is a malignant soft tissue tumor. Despite bland histologic features, a significant number of these tumors metastasize. We describe the clinicopathologic features of 7 new cases of LGFMS including one case of dedifferentiation in a recurrence. MATERIALS AND METHODS: 7 cases obtained from the surgical files of the CHUQ, L'Hôtel-Dieu de Québec or from the consultation files were studied. RESULTS: The patients' age (5 male and 2 female) ranged from 16 to 55 years old. The tumors were located in the thigh (4), the deltoid muscle (2) and in the mesentery (1). They measured from 2.3 to 15 cm (greatest diameter). Histologically, the tumors were characteristically more fibrous than myxoid. Tumors cells were bland, oval to spindle shape, and arranged, at least in part, in a storiform or whorled growth pattern. Cellularity was most prominent in fibrous areas and there were small, sometimes curvilinear vessels in the myxoid areas. Mitotic figures were uncommon. Follow-up of patients ranged from 3 (1/2) months to 22 years. Four patients showed recurrence. One of them demonstrated an area of dedifferentiation into a high grade pleomorphic sarcoma, malignant fibrous histiocytoma (MFH) type. The same patient also had a pulmonary metastasis. CONCLUSION: Differential diagnosis of LGFMS should include intramuscular myxoma, myxoid liposarcoma, myxoid variant of dermatofibrosarcoma protuberans and low grade myxofibrosarcoma. The chimeric FUS/CREB3L2 gene seems to be specific for LGFMS and its expression in the t(7;16)(q33p11) is a useful tool for the differential diagnosis. We report a unique case with areas of high grade sarcoma, MFH type, and areas similar to sclerosing epithelioid fibrosarcoma.

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.

Atypical lipomatous tumor/well-differentiated liposarcoma (ALT-WDLPS) and dedifferentiated liposarcoma (DDLPS) may be difficult to distinguish from benign adipose tumors and from poorly differentiated sarcomas, respectively. Genetically, they are characterized by amplification of MDM2 and CDK4 genes on chromosome 12q13-15. We examined a series of 559 soft tissue tumors (44 ALT-WDLPS, 61 DDLPS, 49 benign adipose tumors, and 405 non-ALT-WDLPS/DDLPS sarcomas) for MDM2 and CDK4 expression using immunohistochemistry. MDM2 and CDK4 immunoexpressions were compared with gene amplification status (as assessed by quantitative PCR and/or comparative genomic hybridization) in 241 neoplasms. Most ALT-WDLPS/DDLPS expressed MDM2 (97%) and CDK4 (92%) as opposed to few benign adipose tumors (MDM2, 5%; CDK4, 2%) and a limited number of non-ALT-WDLSP/DDLPS sarcomas (MDM2, 19%; CDK4, 6%). The sensitivity and specificity of MDM2 and CDK4 immunostainings in identifying ALT-WDLPS/DDLPS among other soft tissue tumors were 97% and 92%, and 83% and 95%, respectively. MDM2 and CDK4 immunostainings were particularly useful to separate ALT-WDLPS from the large group of differentiated adipose tumors, and to distinguish DDLPS from poorly differentiated sarcomas. A strong correlation was observed between MDM2 and CDK4 stainings and gene amplification status. In conclusion, MDM2 and CDK4 immunostainings, which correlate with gene amplification, are helpful adjuncts to differentiate ALT-WDLPS from benign adipose tumors and to separate DDLPS from poorly differentiated sarcomas.

Prognostic significance of lymphovascular invasion in surgically cured rectal carcinoma.

BACKGROUND: Surgery is considered curative in Dukes' B rectal cancer; however, many patients present with early relapse. To identify additional staging information, venous and lymphatic invasion were evaluated as potential prognostic factors. METHODS: Patients with Dukes' B or C rectal disease treated between 1976 and 2001 at a single institution were compared. Patient and treatment characteristics and vascular invasion were documented. The impact of vessel invasion was determined using Cox proportional hazards model. RESULTS: There were 256 Dukes' B patients and 74 Dukes' C cases without vascular invasion. Five-year survival was 76.5% for Dukes' B and 57.1% for Dukes' C patients. Vessel involvement increased the risk of recurrence (hazard ratio [HR] = 3.27, P = .0003) and death (HR = 3.11, P = .002) in B2 patients. The magnitude of these associations were comparable to that of C1 patients for recurrence (HR = 2.81, P = .004) and death (HR = 3.05, P = .005), as well as C2 patients for recurrence (HR = 3.45, P = .0008) and death (HR = 3.87, P = .0005). CONCLUSION: Vascular invasion may be useful in characterizing patients with aggressive Dukes' B disease, who might benefit the most from adjuvant systemic therapy.

The use of clustering software for the classification of comparative genomic hybridization data. an analysis of 109 malignant fibrous histiocytomas.

Malignant fibrous histiocytoma (MFH) is considered the most frequent soft-tissue sarcoma of late adult life. Nevertheless, the validity of this entity has been recurrently questioned by pathologists. Preliminary analyses by comparative genomic hybridization (CGH) of series of MFH have suggested that this tumor group is heterogeneous at the genomic level, and that at least two main genetic subgroups exist. We report an analysis by CGH of a large series of 109 MFH and on the use of clustering software for an objective classification of these tumors. We confirm our preliminary CGH results and demonstrate that two main clusters of tumors are present in the series analyzed.

A subgroup of malignant fibrous histiocytomas is associated with genetic changes similar to those of well-differentiated liposarcomas.

Increasing clinical and pathological evidence suggests that malignant fibrous histiocytomas (MFH) comprise a heterogeneous tumor group. In a series of 108 MFH tested by comparative genomic hybridization, we found in 22 tumors high-level coamplification of the 12q14 approximately q15 chromosome region with other loci, a genetics strongly reminiscent of what has been observed for well-differentiated liposarcomas. Nevertheless, these MFH differ from liposarcomas by a high recurrence of coamplified partners because coamplified loci were seen at 1p32 in nine cases, 6q23 in seven cases, and 12q24 in six cases. The same recurrence was observed in a series of dedifferentiated liposarcomas, but not in a series of well-differentiated liposarcomas. These observations demonstrate that a subgroup of MFH share a genetic partner very similar to that observed in liposarcomas, and suggest that the undifferentiated status of these tumors is closely related to the amplifications of specific chromosome loci.

Fine-needle aspiration of primary and recurrent benign fibrous histiocytoma: classic, aneurysmal, and myxoid variants.

There is a limited number of correlative cytopathological studies of fibrous histiocytoma (FHC). To better define cytopathological criteria of diagnosis, we have reviewed fine-needle aspirates (FNA) from 36 FHCs (32 classical, 1 myxoid, and 3 aneurysmal variants on corresponding histological sections). Original cytological diagnoses were benign in 33 (91.7%) cases (22 accurate) and false positive in 3 (8.3%) cases. All smears were surprisingly homogenous and composed of histiocytic cells with finely vacuolated cytoplasm in 27 (75%) cases, small regular spindle cells in 25 (69%) cases, and giant cells in 17 (47%) cases. Histiocytic cells were attached to vascular structures in 9 (25%) cases. Slight cytonuclear atypia was seen in five (14%) cases. Three (8.3%) cases showed numerous siderophages. In two (5.6%) cases, there were abundant inflammatory backgrounds and in one (3%) case there was a scant myxoid background. Storiform patterns, round cells, prominent atypia, necroses, or mitotic figures were not seen. FHC should be differentiated from other benign, low- and intermediate-grade spindle-cell neoplasms such as low-grade fibrosarcoma, dermatofibrosarcoma protuberans, nodular fasciitis, spindle-cell malignant melanoma, and monophasic synovial sarcoma. Some cases may be misinterpreted as malignant, especially in cases of recurrence or in patients with a cancer history.

Fine-needle aspiration in liposarcoma: cytohistologic correlative study including well-differentiated, myxoid, and pleomorphic variants.

We have reviewed cytopathology and the corresponding histopathology material of 86 liposarcomas (55 patients) seen at Institut Curie. The liposarcomas (LS) were well differentiated in 14 cases (9 pure, 2 dedifferentiated, 3 sclerosing), 64 myxoid, and 8 pleomorphic. Twenty-four tumors were primary, 34 recurrent, and 28 secondary. Smears in LS were composed in different proportions of round, spindle cells, lipoblasts, and myxoid and vascular arborizing structures. Pure well-differentiated LS were frequently composed of lipoblasts, and round or spindle cells were occasionally seen. Dedifferentiated and sclerosing liposarcomas were composed of spindle or round cells, but lipoblasts were also occasionally present. Myxoid or vascular arborizing structures were absent. Myxoid LS (including round and spindle cell LS) frequently showed a myxoid background and less frequently vascular arborizing structures. Tumor cells were round or spindle. Lipoblasts were also seen. Pleomorphic LS were composed of an admixture of all cellular and stromal elements. Well-differentiated LS should be distinguished from hibernoma and spindle cell lipoma, and myxoid LS from myxoma, myxoid chondrosarcoma, chordoma, myxoid leiomyosarcoma, and myxoid malignant fibrous histiocytoma. The demonstration of the specific translocation t(12;16)(q13;p11) of myxoid LS is very helpful to establish the diagnosis. Pleomorphic LS should be differentiated from other high-grade sarcomas, whenever possible.

Fine-needle aspiration of primary and recurrent dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans (DFSP) is a nodular cutaneous mesenchymal tumor of intermediate malignancy. Studies on fine-needle aspiration of DFSP are extremely rare; to our knowledge, only 33 cases have been reported. We have reviewed 14 examples of DFSP in 13 patients. Ten primary tumors were aspirated before surgical biopsy and four recurrent lesions (all from superficial lesions) were also investigated by fine-needle aspiration. All smears were surprisingly homogeneous and composed of isolated spindle cells in all cases (one unsatisfactory smear is excluded). Tissue fragments with a stroriform pattern were seen in 11 cases, fibrillary stromal fragments in 10 cases, naked nuclei in 8 cases, slight to moderate cytonuclear atypia in 5 cases. Mitotic figures, myxoid background, mast cells, and dispersed adipocytes were rare. Giant cells, necrosis, or marked cytonuclear atypia were not seen. DFSP shares morphological characteristics of some low-grade spindle-cell neoplasms. It should be differentiated from other benign low- and intermediate-grade spindle neoplasm such as low-grade fibrosarcoma, fibromyxosarcoma, low-grade malignant peripheral nerve sheath tumor, benign peripheral nerve sheath tumor, nodular fasciitis, and fibrous histiocytoma.

Fine-needle aspiration of leiomyosarcoma: a correlative cytohistopathological study of 96 tumors in 68 patients.

To better define the cytological features of various leiomyosarcoma (LMS) variants, we reviewed the fine-needle aspiration material and the corresponding histologic sections of 96 tumors in 68 patients. Histological variants of LMS were as follows: 80 (83.3%) were of the classical/usual, seven (7.3%) were epithelioid, and nine (9.4%) were myxoid. Review of original cytology reports showed that 23 (24%) tumors were diagnosed as LMS and 69 (71.8%) as other types of malignancies. Two (2.1%) cases were reported as suspicious and two (2.1%) were unsatisfactory. The classical variants of LMS were characterized cytologically by various proportions of spindle-shaped, cohesive, small- or large-sized cells arranged in parallel alignment. Large spindle, round, binucleated, giant cells with intracytoplasmic granulations were frequently seen. Blunt-ended nuclei, intranuclear inclusions and mitotic figures were occasionally seen, as well as stromal fragments. The epithelioid tumors were composed of an admixture of small and large, spindle-shaped and round cells, also arranged in parallel alignment. Tumor cells with granular cytoplasm, blunt-ended nuclei, intranuclear inclusions, mitotic figures, fibrous or myxoid stroma were not observed. The myxoid tumors disclosed large amounts of background myxoid matrix containing large spindle-shaped and giant cells. Entities such as leiomyoma, malignant peripheral nerve sheath tumor, monophasic synovial sarcoma, and malignant fibrous histiocytoma should be considered in the differential diagnosis of LMS of the classical type. Epithelioid leiomyoma may share similar cytological features with epithelioid LMS. The cytological features of the myxoid variant of LMS can be easily confused with other types of benign and malignant mesenchymal tumors depicting degenerative myxoid changes and/or a myxoid matrix component.

Fine-needle sampling in malignant phyllodes tumors: clinicopathologic study of 22 cases seen at the Institut Curie.

The preoperative cytological diagnosis of malignant phyllodes tumor (MPT) is challenging due to the heterogeneity of its clinical, radiological, and morphological presentation. To better define the cytopathological characteristics of MPT, we reviewed 22 examples seen at the Institut Curie. The original cytologic diagnosis was benign breast tumor in four cases (18.2%), suspicious in seven cases (31.8%) (low-grade phyllodes tumor in six cases needing histological evaluation, suspicious of sarcoma in one case), and malignant in 11 cases (50%). Smears were composed of different proportions of clusters of epithelial cells (68.2%), phyllodes fragments (31.8%), spindle cells within stromal tissue (31.8%), isolated spindle-shaped or round cells (45.5%), and bipolar naked nuclei (22.7%). Giant cells and mitotic figures were also occasionally seen. The cytological findings on smears were correlated with histopathological observations. One of the difficulties to reach an accurate cytological diagnosis for MPT is the frequent overwhelming of clearly malignant sarcomatous cell by the presence of largely predominant clusters of epithelial cell.

Cytohistologic correlations in angiosarcoma including classic and epithelioid variants: Institut Curie's experience.

To characterize the cytological features of angiosarcomas, we reviewed the fine-needle aspiration material and corresponding histologic sections of 29 tumors in 23 patients. Histologically, 24 tumors were of the classic type, and 5 were epithelioid angiosarcomas. The original corresponding cytologic diagnoses were as follows: angiosarcoma, 17 cases; sarcoma not otherwise specified, 8 cases; and rhabdomyosarcoma, 1 case. Three samples were cell-poor and were considered suspicious of malignancy. The review of cytology samples showed that smears were cell-rich in 17 tumors and cell-poor in 12 tumors. A hemorrhagic background was present in 9 cases. Tumor cells were polymorphous, including spindle-shaped, round to oval, and polygonal epithelioid cells and giant cells in different proportions. Erythrophagocytosis was seen in 12 tumors. Smears of classic angiosarcomas were polymorphous and lacking specific characteristics, whereas smears of epithelioid tumors were morphologically similar and composed of round to oval and polygonal, epithelial cells frequently arranged in clusters, and showing erythrophagocytosis. The wide spectrum of cellular components of angiosarcomas accounts for the difficulty in establishing accurate tumor typing, particularly with cell-poor samples and low-grade classic angiosarcoma. Entities to consider in the differential diagnosis are carcinoma, epithelioid sarcoma, pleomorphic rhabdomyosarcoma, and malignant melanoma.

Cytohistologic correlations in 56 synovial sarcomas in 36 patients: the Institut Curie experience.

Synovial sarcoma (SS) is a high-grade malignant soft tissue tumor that manifests different phenotypic subtypes that may render their cytologic evaluation challenging. Although several cytologic studies of SS have been published, correlative studies of cytologic and corresponding histologic features are limited. To better define the cytological features of various SS forms, we reviewed the cytologic and the corresponding histologic material of 56 tumors from 36 patients. Classical patterns were defined as dispersed or small clusters of cells with bland chromatin, inconspicuous nucleoli, oval to spindle-shaped cytoplasm and branching tumor tissue fragments, vessel stalks, acinar structures in scant mucin background, seen in all 53 (94.7%) cellular cases. Epithelial, squamous, round cells, mast cells, necrosis, comma-like nuclei, marked nuclear atypia, secretory mucin, and rosette-like structures were also occasionally observed. Comparing the histological subtype we noted that epithelial cells and secretory mucin were restricted to biphasic SS, round cells to poorly differentiated SS, and comma-like nuclei to monophasic fibrous SS. We conclude that the classical pattern is highly suggestive of SS of all three monophasic, biphasic, or poorly differentiated subtypes. These characteristics, along with molecular genetic studies, may improve the cytologic diagnosis of SS.

Cytohistologic correlations of 24 malignant peripheral nerve sheath tumor (MPNST) in 17 patients: the Institut Curie experience.

Cytomorphological patterns of malignant peripheral nerve sheath tumor (MPNST) are insufficiently documented in the literature. Cytological and histological specimens in 24 tumors in 17 patients were correlated. The review of the original cytology reports showed that four (16.6%) tumors were correctly diagnosed, eight (33.3%) were diagnosed as sarcoma not otherwise specified, four (16.7%) as fibrosarcoma, three (12.5%) as synovial sarcoma, three (12.5%) as leiomyosarcoma, and one (4.2%) case each as malignant fibrous histiocytoma and rhabdomyosarcoma. At the review tumors were histologically reclassified as well-differentiated MPNST in 11 (45.9%) cases, anaplastic MPNST in 11 (45.9%) cases, and epithelioid MPNST and malignant Triton tumor in one (4.2%) case each. Cytologically, well-differentiated MPNST were composed of polymorphous oval to round cells, small spindle-shaped cells with wavy and comma-like naked nuclei, and a fibrillary, delicate stroma. Anaplastic MPNST, moreover, were composed of anaplastic giant and polymorphous cells. The malignant Triton tumor was composed of oval to round rhabdomyoblastic cells with eccentric nuclei and the epithelioid MPNST of polymorphous and round, epithelial-like cells. The cytological diagnosis of MPNST may be difficult, especially in anaplastic tumors. The correlation between the cytological features and the clinical information--origin of the tumor from a nerve trunk, a preexisting neurofibroma, patients with known history of neurofibromatosis 1--could be indicative of an MPNST diagnosis.

Comparative fine-needle aspiration and pathologic study of malignant fibrous histiocytoma: cytodiagnostic features of 95 tumors in 71 patients.

To determine diagnostic cytomorphologic features of malignant fibrous histiocytoma (MFH) on fine-needle aspiration (FNA) materials, we reviewed the cytologic material and corresponding histologic slides of 95 tumors in 71 patients. Forty-four (46%) tumors were primary, 38 (40%) were recurrent, and 13 (14%) were metastatic. Histological variants of MFH were as follows: 52 (54.7%, 43 patients) were of the storiform/pleomorphic, seven (7.4%, five patients) were giant cells, four (4.2%, four patients) were inflammatory, and 31 (33.7%, 19 patients) were myxoid type. Review of original cytology reports showed that only 23 (24.2%) tumors were diagnosed as MFH and 68 (71.6%) as other types of malignancies. Four (4.2%) cases were reported as unsatisfactory/suspicious. Our findings showed that spindle-shaped, round, giant cells, osteoclastic-like giant, and inflammatory cells were the most consistent features that allow identification of the storiform/pleomorphic, giant cell, and inflammatory variants of MFH. The myxoid tumors had marked myxoid background matrix with spindle-shaped cells and, less frequently, round and giant cells. Pleomorphic leiomyosarcoma and dedifferentiated liposarcoma should be considered in the differential diagnosis of stroriphorm/pleomorphic, giant cells, and inflammatory variants of MFH. However, myxoid MFH may resemble their leiomyosarcoma and liposarcoma counterparts.

[Does malignant fibrous histiocytoma exist?]. / Requiem pour l'histiocytome fibreux malin?

Malignant fibrous histiocytoma (MFH) has come to be regarded as the most common malignant neoplasm of the mesenchymal soft tissues. It designates a spectrum of tumors which share morphologic features that allow their inclusion in a distinct clinicopathologic setting, although being not uniform in their histogenesis and pathogenesis. Clinicopathologic variants include the following: the storiform-pleomorphic form of MFH, the myxoid type of MFH, the giant cell type of MFH and the inflammatory type. The latter group, the angiomatoid variant, has been reclassified within the fibrohistiocytic tumors of low malignant potential. Tissue culture, ultrastructural and immunohistochemical studies have both endorsed or refuted the validity of the concept. As a whole, these morphologic studies which attempted to characterize MFH were not able to delineate specific markers or to describe the phenotype of this sarcoma of supposed fibrohistiocytic lineage. There is growing evidence that MFH is a second component in another sarcoma and represents a morphologic modulation resulting from tumor progression. Recent cytogenetic and molecular genetic investigations are consistent with that hypothesis: a comparative analysis between the most frequent genomic imbalances observed in series of MFH and leiomyosarcomas (LMS) demonstrated that both tumors had similar recurrent imbalances. Immunohistochemical and molecular biologic investigations have shown similar targets of chromosome deletions in both tumors. A new classification of soft tissue sarcoma based on molecular parameters is nevertheless premature. The morphologic characterization of MFH and its sub-types provides the clinician with unique information in the management of these tumors, by identifying a spectrum of tumors with well-recognized clinical profiles.

[Unusual parosteal osteochondromatous proliferation or Nora's tumor. A clinicopathological analysis of 4 cases]. / Prolifération ostéocartilagineuse parostéale bizarre ou tumeur de Nora. A propos de quatre observations.

Nora's lesion, also known as bizarre parosteal osteochondromatous proliferation (B.P.O.P.), involves mostly the small tubular bones of the hands and feet. Histologically, it is characterized by a proliferation of chondroid, bony and fibrous tissues, sometimes with high cellular density, bizarre chondrocytes but is devoid of cellular atypia and necrosis. Distinct blue color is noted at the interface of bone and cartilage. The most important lesions that present differential diagnostic problems are chondrosarcoma, parosteal osteosarcoma and florid reactive periostitis. The lesion is benign but may recur locally in as many as 55%. The clinical and pathological findings of four cases of Nora's lesion are presented.