proliferative myositis and fasciitis : a light and electron microscopic, cytologic, dna-cytometric...

APMIS 100: 437448, 1992

Proliferative myositis and fasciitis A light and electron microscopic, cytologic, DNA-cytometric and

immuno his t ochemical study

LARS LUNDGREN’, LARS-GUNNAR KINDBLOM’, JAN WILLEMS2, URSULA FALKMER2 and LENNART ANGERVALL

‘Departments of Pathology, Sahlgren Hospital, University of Gothenburg, Gothenburg and *Karolinska Hospital, Stockholm, Sweden

Lundgren, L., Kindblom, L-G., Willems J., Falkmer, U. & Angervall, L. Proliferative myositis and fasciitis. APMIS 100: 437-448, 1992.

Two cases of proliferative myositis, four cases of proliferative fasciitis and one mixed form of proliferative myositis and fasciitis have been analyzed in terms of cell differentiation and DNA content. Light microscopically, the lesions were characterized by a mixture of proliferating spindle- shaped cells and uni-, bi- or occasionally multinucleated ganglion cell-like cells. The spindle cells showed ultrastructural features and immunohistochemical properties, including an immunoreactivity for smooth muscle-specific actin, indicative of a myofibroblastic differentiation. The ganglion cell- like cells displayed some resemblance to active osteoblasts ultrastructurally and differed immunohistochemically from the spindle cells by being non-immunoreactive for smooth muscle-specific actin. None of the two cell types showed immunoreactivity for desmin, myoglobin or factor VIII RAG. It is suggested that the two cell types represent different lines of cell differentiation. The cytologic features in smears, as seen in two cases of proliferative fasciitis and one case of proliferative myositis, are considered to be characteristic of these lesions and to permit the diagnosis to be made by fine- needle aspiration. In two of the cases, the lesion was diagnosed only cytologically and thereafter disappeared spontaneously within a month. Cytometric DNA measurements, using two different image analysis systems on Feulgen-stained sections and smears, revealed a “diploid” spindle-shaped cell population with a variable proportion of cells with scattered DNA values. The ganglion cell-like cells differed from the spindle cells by having a broad DNA peak in the diploid region and additional peaks in the tetraploid region, as well as a higher proportion of cells with scattered DNA values compared with those of the spindle-shaped cells. The results of the quantitative DNA analysis are well in keeping with the benign and proliferative nature of these lesions. However, with the technique used here, quantitative DNA analysis, does not distinguish these pseudosarcomatous fibrous lesions from diploid and tetraploid soft tissue sarcomas.

Key words: Cytology; DNA analysis; fine-needle aspiration; immunohistochemistry; proliferative fasciitis; proliferative myositis; pseudosarcoma; ultrastructure.

Lars Lundgren, Department of Pathology, Sahlgren Hospital, S-413 45 Gothenburg, Sweden.

Proliferative myositis (2 1) and proliferative fasciitis (8) are closely related lesions within the group of so-called pseudosarcomatous lesions of soft tissues and have many features in common with nodular fasciitis, the most common form of pseudosarcomatous lesion (1 1). The

Received July 7, 1991. Accepted October 21, 1991

lesions differ mainly in location; proliferative myositis is intramuscular, while proliferative fasciitis involves the fascia and interlobular fibrous septa of the subcutaneous fat (15). Mixed forms have also been reported (1 1). Light microscopically, proliferative myositis and proliferative fasciitis are lesions characterized by the predominance of large, usually mono- or binu- cleated ganglion cell-like cells and proliferating spindle cells. The ganglion cell-like cells have

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been the subject of interest since their origin is uncertain and they may be misinterpreted as being malignant. It has been suggested that these cells are of myogenic origin because of their cytoplasmic fuchsinophilia when using tri- chrome staining (21). It has also been suggested that they represent fibroblasts or fibroblasts act- ing as facultative histiocytes (8, 14). The few ultrastructural and immunohistochemical studies of proliferative fasciitis and proliferative myositis which have been conducted have not solved this problem; the ganglion cell-like cells have been reported to show histiocytic, fibroblastic or myofibroblastic features ( 5 , 8, 9, 19, 26, 29, 32, 34). The fine-needle aspiration cytology has previously been described in two cases of proliferative myositis (28).

The diffuse infiltrative growth, high cellularity, mitotic activity and the presence of ganglion cell-like giant cells have led to the mis- interpretation of proliferative fasciitis and myositis as rhabdomyosarcoma, ganglioneuroblas- toma and other types of malignant neoplasms (15): It has been suggested that quantitative DNA analysis may be of value when it comes to distinguishing between benign and malignant soft tissue tumors on the assumption that sarcomas are often aneuploid (22). There are, however, soft tissue sarcomas of moderate and high grade which are diploid and tetraploid (1, 13, 22,27,3 l), and so far no systematic DNA analysis of pseudosarcomatous lesions of soft tissues has been performed.

The present investigation aims to further characterize the two cell types of proliferative fasciitis and myositis by a light and electron microscopic and immunohistochemical study and quantitative DNA analysis, and to describe the fine-needle aspiration cytology findings of these lesions.

MATERIALS AND METHODS

Four cases of proliferative fasciitis and one case of proliferative myositis were accrued from the files of the Department of Pathology at Sahlgren Hospital, Gothenburg and Karolinska Hospital, Stockholm, Sweden between 1972 and 1990. Another case of proliferative myositis and one case of a mixed form of proliferative fasciitis and myositis were obtained

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from a Swedish national series of tumors reported to the Swedish Cancer Registry during the years 1958 to 1976 as soft tissue sarcomas. Both cases of proliferative myositis and one of the cases of proliferative fasciitis had been initially diagnosed as rhabdomyosarcoma. Data were obtained from clinical rec- ords.

For light microscopy, 4-pm sections were cut from the paraffin blocks and stained with van Gieson tri- chrome and hematoxylin-eosin.

Fine-needle aspiration for the preoperative diagnosis was performed on two of the patients with proliferative fasciitis and on one patient with proliferative myositis. Some of the smears were air-dried and May-Griinwald-Giemsa (MGG) stained, while others were fixed in 95% methanol prior to Papanicolaou (Pap) staining. In one case of proliferative fasciitis and in the case of proliferative myositis, the lesions were not removed surgically as the masses rapidly diminished in size after the fine-needle aspiration. Both lesions disappeared spontaneously within a month. In the other case of proliferative fasciitis, an inconclusive cytologic diagnosis was rendered prior to the light microscopic examination of a surgical specimen.

Three cases of proliferative fasciitis, one case of proliferative myositis and the case with a mixed appearance of proliferative fasciitis and myositis were studied ultrastructurally. In three cases the material for electron microscopy was initially fixed in 4% formaldehyde. Small pieces of this tissue were rinsed in buffer for 24 h and then postfixed with 1% osmium tetroxide for one h, dehydrated in ethanol and embedded in epoxy resin. In the other two cases only paraffin-embedded material was available. Small pieces of tumor tissue from selected areas of the paraffin blocks were cut out and thereafter processed for electron microscopy (30, 36). One pm-thick sections were stained with toluidine blue and ultrathin sections cut on an LKB Ultrotome 111 were contrast stained with uranyl acetate and lead citrate and examined under a Philips 400 electron microscope.

For the immunohistochemical analysis the avidin- biotin complex (ABC) method was applied to formalin-fixed and paraffin-embedded tissues (20). Prior to staining the paraffin sections were deparaffinized in xylene. For factor VIII RAG and desmin the sections were predigested with 0.05% trypsin (type III- S, Sigma Chemical Company, St Louis, USA) in 0.05 M TBS, pH 7.8, for 20 min at 37°C. All sections were then treated with 0.5% H202 in methanol in order to reduce endogenous peroxidase activity. The ABC method was performed using the VectastainB ABC kits (Vectastain, Vector Labs, Burlingame, CA, USA) according to the instructions except for a prolonged incubation time for the primary antisera (1 6 h at 4 ) as previously described (25). The end products were visualized by treating the sections with a freshly made solution of 0.05% diaminobenzidine hydrochloride

PROLIFERATIVE MYOSITIS AND FASCIITIS

with 0.02% H,Oz in TBS, pH 7.4. The specifications of the primary antisera used are given in Table 2.

DNA measurements were made in four cases of proliferative fasciitis and two cases of proliferative myositis by means of image cytometric DNA assessments of paraffin sections. This technique has previously been described in detail (2,4,7,23). The 4 pm- thick sections of the originally formaldehyde-fixed paraftin-embedded specimens were cut, deparaffinized and refixed in neutral-buffered 4% formaldehyde solution before staining according to the Feulgen technique (with acid hydrolysis in 5 N HCl at room temperature for 60 min) (17). The air-dried fine- needle aspiration biopsy specimens were fixed and stained in the same manner. The original May- Griinwald-Giemsa-stained smear specimens were destained as previously described (16), refixed, and stained according to the procedure described above. Cytometric DNA assessments were made using two different image analysis systems. All the specimens were measured using a rapid scanning and integrating microspectrophotometer (6, 7) and an image analysis system, based on a video-CCD camera (3). For each specimen, the two different cellular components of the proliferative lesions, i.e. the spindle cells and the ganglion cell-like cells, were measured separately. The integrated optical density of at least 100 structurally well-preserved cell nuclei was measured at a wave- length of 546 nm, avoiding nuclei lying too close together or overlapping one another, as well as nuclei showing obvious nuclear membrane damage (most probably cutting artefacts). As an internal standard, at least 20 nuclei of endothelial cells or lymphocytes were assessed concomitantly; their median density value was adopted as the “diploid” DNA value. All the specimens were measured twice and indepen- dently by two of us (LL and JW). The DNA histograms which were obtained were classified as “diploid”, “tetraploid”, or “aneuploid”, using the modal value (MV) of the internal control cells (2). “Diploid” histograms were characterized by a single distinct peak with an MV of < 2.5 c. “Tetraploid” histograms often had two peaks: a distinct one in the diploid region and an additional one in the tetraploid region, i.e. between 3.5 c and 4.5 c. The cell population was defined as “tetraploid” when the tetraploid peak contained > 20% of all cells counted in the histogram. “Aneuploid” DNA histograms show distinct peaks at any position outside the diploid and tetraploid range or one diploid andlor one tetraploid peak in combination with > 15% of the cells measured as scattered DNA values outside these peaks.

RESULTS

Data on the age and sex of the patients, tumor site and size, treatment and follow-up are summarized in Table 1.

Light microscopic appearance The three cases of proliferative fasciitis had a

similar appearance; they all presented poorly circumscribed lesions within the subcutaneous tissue extending along fibrous septa of the adi- pose tissue. In an additional case, the lesion also involved the underlying muscle fascia and superficial parts of the muscle, i.e. a mixed form of proliferative myositis and fasciitis. The lesions were characterized by mostly haphaz- ardly arranged, slender, fibroblast-like spindle cells and numerous large cells with one or two vesicular nuclei with a prominent nucleolus, giving them a ganglion cell-like appearance (Fig. IA). The cytoplasm of such cells was rounded, polygonal or occasionally elongated, and dense and basophilic in the hematoxylin-eosin-stained sections. The matrix was mostly loose with varying amounts of mucosubstance and collagen, and contained numerous radiating capillaries in areas. The mitotic activity in the lesions varied between 3 and 8 mitoses per mm2 (median 6), evenly distributed between spindle cells and ganglion cell-like cells. In one case a tripolar mitosis was seen.

The surgically removed lesion of proliferative myositis was superficially located in the muscle and was characterized by similar proliferating fibroblast-like spindle cells and ganglion cell- like giant cells. These cells appeared within the epimysium, perimysium and endomysium with uninvolved or atrophic muscle fibers in between (Fig. lB), giving the lesion a network appearance when examined at low magnification. There were mitotic figures among both fibroblast-like and ganglion cell-like cells.

Immunohistochemical analysis The results of the immunohistochemical

analysis are summarized in Table 2. The spindle cells and the ganglion cell-like

cells generally showed a strong immunoreactivity for vimentin (Fig. IE). The ganglion cell-like cells were either intensely stained throughout the cytoplasm or contained fairly well-demarcated segments with concentrated immunoreactivity contrasting with non-immunoreactive areas of the cytoplasm. The endothelium and also parts of the smooth muscle of vessels displayed immunoreactivity for vimentin, whereas the skeletal muscle was non-immunoreactive. Almost all the

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TABLE 1. Clinical data for four cases of proliferative fasciitis (PF) , two cases of proliferative myositis ( P M ) and one case of a mixed form of proliferative fasciitis and myositis (PF&PM).

Case Diag- Age, Sex Size, Location Cytology Diagnostic procedure Follow-up nosis years cm & treatment PF&PM 69

PF 60

PF 55

PF 54

PM 75

PF 46

PM 68

M

F

M

F

F

F

F

2.5 x 2.5 Subcutaneous and superficial in the right pect. muscle

5 x 5 Subcutaneous, abdo- minal wall

4 x 1 Subcutaneous, left breast, adjacent to the pect. muscle

1.5 x 1.5 Subcutaneous, left groin

3.5 x 3.5 Intramuscular, ad- ductor muscle of left thigh

3 x 3 Subcutaneous, back

5 x 5 Intramuscular, left sternocleidomastoid muscle

Primary local excision, followed by re- moval of the pect. muscle and axillary lymph nodes

X FNA, radiotherapy followed by local excision Local excision

Local excision

Local excision

X FNA, disappeared

X FNA, disappeared spontaneously

spontaneously

15 years, alive and well

14 years, alive and well

Two years, alive and well

Two years, alive and well No data

Three years, alive and well One year, alive and well

spindle cells harbored actin (N 350), whereas the actin immunoreactivity of the ganglion cell- like cells varied considerably (Fig. 1F). Many of these cells showed no immunoreactivity at all, whereas some of them displayed immunoreactive staining in segments of the cytoplasm and a few were strongly stained throughout the cytoplasm. In all the lesions, a varying proportion of spindle cells harbored immunoreactivity for smooth muscle-specific actin, whereas the ganglion cell-like cells were non-immunoreac-

tive (Fig. 1G). In the surrounding tissue, the smooth muscle of vessels displayed immunoreactivity; the skeletal muscle cells did not. Both the spindle cells and the ganglion cell-like cells were non-immunoreactive for desmin and myoglobin, whereas the skeletal muscle fibers in- cluded in the same sections displayed immunoreactivity for both antigens. The two cell types were also non-immunoreactive for factor VIII RAG, whereas the endothelium of the abundant capillaries harbored this immunoreactivity.

Fig. I . A. Proliferative fasciitis. Characteristic area composed of a mixture of slender spindle cells and larger cells with a densely stained abundant cytoplasm and one or two vesicular nuclei with prominent nucleoli, giving them a ganglion cell-like appearance (H&E), x 80. B. Proliferative myositis. Spindle cells and ganglion cell-like cells similar to those seen in proliferative fasciitis can be seen between split-up atrophic muscle fibers (H&E), x 40. C & D. Smears from a case of proliferative fasciitis showing spindle cells and mono- and binuclear ganglion cell-like cells. May-Grunwald-Giemsa stain (C) and Papanicolaou stain (D), x 160. E. Spindle cells and ganglion cell-like cells positively stained for vimentin, x 40. F. The spindle cells are positive for actin, while the positivity of the ganglion cell-like cells varies, x 80. G. Spindle cells are positively stained for smooth muscle-specific actin, while ganglion cell-like cells are negative. (E, F and G: ABC technique with hematoxylin counterstaining.) x 40.

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TABLE 2. Result of the irnmunohistochemical analysis in five cases of proliferative myositis and fasciitis and specijkation of antibodies used

Antibody Spindle cells Ganglion cell-like cells Positive internal control Anti-vimentin V9'" + + + +++ Fibroblasts, endothelium Anti-desmin D 33" - - Smooth and striated muscle Anti-actin N 350(3)* + + + + t o ++ Smooth muscle and endothelium of vessels,

Anti-aSMl-a~tin'~) + t o + + - Smooth muscle of vessels, pericytes Myoglobin MG-l(5) - - Striated muscle FVIII RAG'') - - Endothelium + + + all cells positive; + + many cells positive; + a few cells positive; - no positivity. * Somewhat disturbing background staining. 1 . Dakopatts, Copenhagen, Denmark; 2. Sanbio, Nistelrode, Holland; 3. Amersham, Buckinghamshire, En- gland; 4. Gift from Prof. G. Gabbiani, Geneva, Switzerland; 5. Bio-Yeda, Rehovat, Israel.

fibroblasts*

Electron microscopic appearance The large ganglion cell-like cells had a similar

appearance in all the cases. The cells were mostly rounded, oval or polygonal with one or two central nuclei. Occasionally the cells were elongated with a peripheral nucleus. The nuclei were mostly rounded with smooth outlines, but they were sometimes deeply clefted with cytoplasmic pseudoinclusions (Fig. 2A). The chromatin was evenly distributed and finely dispersed with a thin zone of heterochromatin along the nuclear membrane. The large nucleoli were very dense or reticular, and occasionally with a marginal location. The abundant cytoplasm of these cells was dominated by rough endoplasmic reticulum (RER) and cytofilaments. The RER formed both narrow arrays and dilated cisternae which were filled with granular dense material and intimately associated with mitochondria (Fig. 2B). The mitochondria varied considerably in size; many of them were long and slender. The cytofilaments were of intermediate type and formed a network throughout the cytoplasm of most cells and also densely packed whorled structures which completely occupied parts of the cytoplasm in many cells (Fig. 3). Sparse amounts of thin filaments of actin type arranged in parallel along the cytoplasmic membrane were identified in some cells, but there were no elongated condensations. Single dense fibers or bundles of these fibers were found in a few cells, sometimes showing the cross-banded structure of mature collagen, thereby indicating intracytoplasmic collagen formation. The cytoplasmic membrane formed numerous projections (Fig. 2A) and, especially in areas where several cells were grouped closely together, they inter-

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digitated and were occasionally connected by tight junctions, desmosomes or hemidesmoso- mes. The irregularly contoured cytoplasmic membrane sometimes formed deep invaginations filled with collagen bundles. There was no external lamina surrounding the cells.

The spindle cells of both the proliferative myositis and fasciitis had fibroblastic and myofibroblastic features. The oval nuclei of these cells had a denser chromatin texture than the nuclei of the ganglion cell-like cells and they sometimes revealed a prominent nuclear fibrous lamina. The cytoplasm was dominated by RER. In addition, the spindle cells contained a network of intermediate cytofilaments, albeit less conspicuous and lacking the dense filament whorls seen in the ganglion cell-like cells. There were spindle cells with abundant thin filaments which formed bundles arranged along the cytoplasmic membrane (Fig. 4). Poorly developed elongated condensations were identified within these filament bundles (Fig. 5) . Pinocytotic vesicles along the cytoplasmic membrane were a prominent finding and an incomplete external lamina could occasionally be identified.

Cytologic appearance Fine-needle aspirates from two cases of pro-

liferative fasciitis and one case of proliferative myositis showed a dual composition of cells. One type was large, oval and ganglion cell-like with a cytoplasm which was dense in the center of the cell, while a zone with minute, optically empty vacuoles was seen at the periphery (Fig. 1C). The round or oval nuclei were located pe- ripherally and varied somewhat in size from cell to cell, but in cells with two, or occasionally

PROLIFERATJVE MYOSJTIS AND FASCIITIS

Fig. 2. A & B. Ganglion cell-like cells with a rounded nucleus with smooth or convoluted contours and an abundant cytoplasm dominated by RER, partly forming wide cisternae filled with granular material (c). The cytoplasmic membrane forms numerous projections. A x 3500, B x 9000.

more, nuclei they were of equal size. The nuclei contained prominent nucleoli and revealed a f i - nely granulated chromatin which varied in stainability. The nuclear membrane stood out sharp- ly, especially in Pap-stained smears (Fig. 1D).

The second type of cell was spindle-shaped and fibroblast-like with a single, oval or elongated nucleus with one or more minute nucleoli. The chromatin was mostly moderately granular, but in a few cells the nucleus was enlarged and hyperchromatic. In the smears from the case of proliferative myositis there were also many dispersed fragments of striated muscle cells. In one case of proliferative fasciitis, the background consisted of a small amount of mucous material which stained slightly pink in MGG- stained smears.

Cytometric DNA analysis The DNA histograms obtained using the two

different sets of equipment produced essentially the same results, as did the repeated measurements performed by each of two pathologists. In all the specimens of proliferative myositis and fasciitis, the DNA patterns of the spindle- shaped cells displayed a main peak in the diploid region. The percentage of cells with scattered DNA values varied, < 15%, and some cells had DNA values in the tetraploid region (Fig. 6A). The coefficient of variation (CV) (2) of the diploid peaks ranged from 8.0% to 14.3%, with a mean of 11.2%. The histograms of the nuclei of the spindle-shaped cells in the cytodiagnostic smears showed essentially the same DNA distri- butions as those in the cut sections. Moreover,

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LUNDGREN et al

Fig. 3. Cytoplasmic area of a ganglion cell-like cell dominated by whorls of intermediate filaments. x 19000.

the CVs of their main histogram peaks were not significantly lower.

The DNA distribution patterns of the individ- ual nuclei of the ganglion cell-like cells in the specimens of proliferative myositis and fasciitis differed from those obtained for the spindle cells (Fig. 6B). Most cytometric DNA histograms showed broad peaks in the diploid region and additional peaks in the tetraploid region. The CVs were higher than the CVs of the peaks in the DNA histograms of the nuclei of the spindle- shaped cells (from 11.7% to l6.8%, mean 14.8%). The bi-or occasionally multinucleated ganglion cell-like cells showed tetraploid or even octaploid nuclear DNA values. The percentages of cells with scattered values outside the peaks appeared to be somewhat higher than those found in the DNA histograms of the nuclei of the spindle-shaped cells. These values were not actually calculated as a result of the relatively high CVs of the main peaks. There were no

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Fig. 4. Spindle cell with prominent bundles of thin filaments of actin type and a moderate amount of RER. x6400.

DNA histograms of "aneuploid" type in this series.

DISCUSSION

All seven lesions in this series were clinically and light microscopically characteristic cases of proliferative myositis and fasciitis; one of them was a mixed form and all of them showed an abundance of ganglion cell-like cells. The light and electron microscopic and immunohistochemical analysis did not reveal any difference between the cells of proliferative myositis and fasciitis. The demonstrations of vimentin and smooth muscle-specific actin but not of desmin, myoglobin and factor VIII in the spindle-shaped cells indicates that they are of myofibroblastic origin. Furthermore, the ultrastructural findings of actin filament bundles with elongated condensations, occasional external laminae par-


Fig. 5. Cytoplasmic projections of spindle cells with bundles of thin filaments concentrated beneath the cytoplasmic membrane. Some longitudinal condensations are seen. x 30000.

tially enclosing the cells, perinuclear fibrous laminae and pinocytotic vesicles further support their myofibroblastic differentiation.

On the basis of the abundance of RER and thin filaments of actin type, it has been suggested that the ganglion cell-like cells represent modified fibroblasts (9, 15, 34). In the present study, these cells were found to differ from the spindle cells electron microscopically and also immunohistochemically by being irregularly immunoreactive for actin and non-immunoreactive for smooth muscle-specific actin. Cells with features intermediate to those of the spindle cells and the ganglion cell-like cells were not identified. The mitotic activity among both cell types militates against the idea that the ganglion cell- like cells represent an end-stage of a modified fibroblast. Ultrastructurally, these cells had some features of active osteoblasts. They there- fore showed an abundance of RER, forming

2c 4c 6c DNA (relunits)

aQ

2c 4c 6c

DNA (rel.units) Fig. 6. Image cytometric DNA histograms, obtained on 4 pm-thick paraffin sections from specimens of proliferative myositis and fasciitis. A. The DNA histogram of the spindle-shaped cells shows a broad peak in the 2c region with some (< 15%) scattered values between the 2c (the “diploid”) and 4c (the “tetraploid”) region, indicating the presence of proliferating DNA-‘‘diploid’’ cells. B. The DNA histogram of the ganglion cell-like cells shows, in addition to the main “diploid” peak with “scattered cells”, a high fraction of DNA values also in the 4c region, indicating the presence of proliferating DNA-“diploid” cells with an accumulation of cells in the G2 phase, i.e. polyploidization.

both narrow parallel arrays and cisternae filled with dense material, and prominent cytoplasmic projections, and were intimately associated with collagen. Intracytoplasmic collagen production, as seen in some of the ganglion cell-like cells, has been found in a large variety of cells, including osteoblasts (18, 24, 34). Bearing in mind the resemblance to osteoblasts, it is interesting to

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LUNDGREN el al.

note that proliferative myositis may produce osteoid and bone at times (10, 15). It has been suggested that the eosinophilic inclusions described in some ganglion cell-like cells represent collagen within the cells (15). In view of the very sparse amount of intracytoplasmic collagen seen in a few cells, it seems more likely that the inclusions represent collagen material within the numerous deep cytoplasmic invaginations seen in many of the cells at the electron microscopic examination. Furthermore, the finding of factor XIIIa in the ganglion cell-like cells, considered by Ushigome et al. and co-workers to support a fibroblastic nature, has also been demonstrated in osteoblasts (34).

The cytologic findings in the fine-needle aspirates of proliferative fasciitis and proliferative myositis were comparable in part to those of nodular fasciitis (12), but differed in the prominent component of large ganglion cell-like cells. The cytology in our cases is also in accordance with two cases described previously (28), and we believe that the cytologic appearance in smears from proliferative myositis and proliferative fasciitis is fairly charcteristic and permits a definite diagnosis, as long as the clinical findings are in accordance with the diagnosis. As a result of cellularity, mitotic activity and the presence of large ganglion cell-like cells there is a risk that these lesions may be confused cytologically with malignancy, especially the pleomorphic variant of malignant fibrous histiocytoma. However, the giant cells and spindle cells seen in aspirates from malignant fibrous histiocytoma have a more irregular nuclear form and chromatin pattern, and lack the cytoplasmic features of the ganglion cell-like cells (35). Two cases in our series (cases 6 and 7) are of considerable interest because the diagnosis was confirmed by the fine- needle aspiration cytology alone and because both lesions showed complete spontaneous re- gression, as described in cases of nodular fasciitis (1 5).

Cytometric DNA assessment of cell nuclei made on sections is a somewhat crude technique (2, 3,4, 23). Admittedly, great opportunities for introducing artefacts are presented when measurements are made of differently cut nuclei which vary in shape, chromatin distribution and staining properties. Against this background, it should be noted that there were no significant differences in the results of the intra- and interob-

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server assessments of the cytometric DNA histograms. Furthermore, the DNA assessments made of the cytodiagnostic specimens and the cut sections produced the same results with more or less the same CVs in the main peaks. The slight differences in the results found between the spindle-shaped cell population and the ganglion cell-like cells (Fig. 6) make it obvious that DNA measurements of such specimens have to be made very selectively and with a specific knowledge of their cellular peculiarities. The diploid DNA distribution patterns of the spindle-shaped cells appear to represent diploid proliferating cells (33). The cytometric DNA distribution patterns of the ganglion cell-like cells, which are predominantly of polyploid (tetra- and octaploid) type with high numbers of cells with scattered DNA values in the histograms, suggest that these cells are even more proliferative than the spindle-shaped cells (33). The occurrence of polyploid cell popula- tions, however, also indicates an accumulation of ganglion cell-like cells in the G2 phase. Such an accumulation of “G2 phase cells” may possibly be due to a cell-cycle block of a temporary or per- manent nature. Whether or not the formation of this cell type with its characteristic nuclear features, in terms of both structure and nuclear DNA content, is a degenerative phenomenon is unclear. It is also unknown whether or not the proportion of spindle-shaped cells and ganglion cell-like cells changes during the relatively short clinical course of these lesions. No cytometrically aneuploid DNA distribution patterns were ob- served, thereby supporting the benign character of these proliferative fibrous lesions. On the other hand, the differential diagnostic value of cytometric DNA measurements between proliferative myositis and fasciitis and soft tissue sarcomas is small, since not only low grade sarcomas but also some entities of soft tissue sarcoma of moderate and high grade malignancy, such as alveolar soft part sarcoma (27), epithelioid sarcoma (31), syn- ovial sarcoma (1) and angiosarcoma (13,22, own unpublished observations), may have a diploid or tetraploid DNA distribution pattern.

This study was supported by research grants from the Gothenburg Medical Society, the Swedish Cancer Society, the Swedish Medical Research Council (Pro- ject No. 718), the Cancer Society of Stockholm, and the King Gustav V Jubilee Fmd, and by the research funds of the Faculties of Medicine at the Karolinska Institute, Stockholm and the University of Gothenburg.


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