Bull. Org. mond. San 11974,) 50, 101-110 Bull. Wid Hith Org.j VIII. Tumours of the soft (mesenchymal) tissues E. WEISS 1 This is a classification oftumours offibrous tissue, fat, muscle, blood and lymph vessels, and mast cells, irrespective of the region of the body in which they arise. Tumours offibrous tissue are divided into fibroma, fibrosarcoma (including " canine haemangiopericytoma "), other sarcomas, equine sarcoid, and various tumour-like lesions. The histological appearance of the tamours is described and illustrated with photographs. For the purpose of this classification " soft tis- autonomic nervous system, the paraganglionic struc- sues" are defined as including all nonepithelial tures, and the mesothelial and synovial tissues. extraskeletal tissues of the body with the exception of This classification was developed together with the haematopoietic and lymphoid tissues, the glia, that of the skin (Part VII, page 79), and in describing the neuroectodermal tissues of the peripheral and some of the tumours reference is made to the skin. HISTOLOGICAL CLASSIFICATION AND NOMENCLATURE OF TUMOURS OF THE SOFT (MESENCHYMAL) TISSUES I. TUMOURS OF FIBROUS TISSUE C. RHABDOMYOMA A. FIBROMA D. RHABDOMYOSARCOMA 1. Fibroma durum IV. TUMOURS OF BLOOD AND 2. Fibroma molle LYMPH VESSELS 3. Myxoma (myxofibroma) A. CAVERNOUS HAEMANGIOMA B. FIBROSARCOMA B. MALIGNANT HAEMANGIOENDOTHELIOMA (ANGIO- 1. Fibrosarcoma SARCOMA) 2. " Canine haemangiopericytoma" C. GLOMUS TUMOUR C. OTHER SARCOMAS D. LYMPHANGIOMA D. EQUINE SARCOID E. LYMPHANGIOSARCOMA (MALIGNANT LYMPH- E. TUMOUR-LIKE LESIONS ANGIOMA) 1. Cutaneous fibrous polyp F. TUMOUR-LIKE LESIONS 2. Keloid and hyperplastic scar V. MESENCHYMAL TUMOURS OF 3. Calcinosis circumscripta PERIPHERAL NERVES II. TUMOURS OF FAT TISSUE VI. MAST CELL TUMOUR A. LIPOMA (MASTOCYTOMA) VII. CANINE HISTIOCYTOMA B. LIPOSARCOMA VIII. RETICULOSARCOMA III. TUMOURS OF MUSCLE TISSUE (CUTANEOUS RETICULOSIS) A. LEIOMYOMA IX. MISCELLANEOUS TUMOURS B. LEIOMYOSARCOMA X. UNCLASSIFIED TUMOURS However, as the classification is applicable to soft 1 Veterinar-Pathologisches Institut der Justus Liebig- tissue tumours in all parts of the body, it is published Universitat, Frankfurterstrasse 94, 6300 Giessen, Federal Republic of Germany. separately, as in the case of the WHO classification of the human tumours.a It is based on the study of a Enzinger, F. M. et al. Histological typing of soft tissue tumours, Geneva, WHO, 1963. some 2 500 tumours, mostly from dogs. 3170 101 - 8 102 E. WEISS DESCRIPTION OF TUMOURS I. TUMOURS OF FIBROUS TISSUE relatively few areas of the tumour. The main tumour mass is similar to a fibrosarcoma. Therefore the A. Fibroma tumour should not be called " haemangiosarcoma ". 1. Fibroma durum (Fig. 1). This benign tumour Furthermore the designations " haemangiopericy- consists of a dense growth of mature fibrocytes and toma " and " malignant pericytoma " are not cor- collagenous fibrous connective tissue. The spindle- rect, because the onion-skin structures alone furnish shaped or ovoid nuclei of the tumour cells are no real proof of the origin of the tumour cells from relatively poor in chromatin. The collagenous fibres pericytes. A variant of the tumour shows radial are usually arranged in fascicles, more rarely in arrangement (cuffing) of spindle-shaped hyperchro- whorls. matic cells around small blood-vessels (not capil- laries) within areas of mucinous degeneration or molle This tumour is 2. Fibroma (Fig. 2). benign necrosis. The " cuffed " blood-vessels always show soft and has less dense connective tissue. The tumour open lumina and frequently hyalinized walls. The cells are often stellate. Fat tissue may be present. peripheral cells of these " tumour-islands " invade 3. Myxoma (myxofibroma). This benign tumour the surrounding necrotic area like fibroblasts in is similar to fibroma molle, but shows mucinous tissue culture. The perithelioma-like structures can be material in varying amounts. explained as growth of tumour cells along blood vessels within necrotic areas. The so-called " canine B. Fibrosarcoma (Fig. 3) haemangiopericytoma" is most often seen in old 1. Fibrosarcoma. This is a circumscribed or dogs. The tumour may be up to 25 cm in diameter, infiltrating tumour composed of collagenous and greyish-white, firm, and lobulated. It is common reticulin fibres and tumour cells. The tumour cells, within the soft tissue of the skin and muscles, spindle-shaped or stellate, are irregularly arranged. predominantly of the thighs and trunk. Recurrences They show anisomorphic nuclei and varying num- after excision are common (25-50%), whereas meta- bers of mitotic figures. So-called spindle cell sarco- stases are frequent only in the necrotic type. mas are included under this heading, but the term has been abandoned in favour of " fibrosarcoma ", C. Other sarcomas since the former always-at least in some areas- Histologically, these sarcomas are characterized by shows collagenous fibres. Usually the diagnosis of the pleomorphism of the tumour cells. Cells similar fibrosarcoma is made only on the basis of the to undifferentiated reticulum cells, epitheloid cells, histological criteria mentioned above, but it should and giant cells with one or more nuclei are present. be kept in mind that most of these tumours, although Mitotic figures are common. Collagenous and reti- they look malignant, are actually benign. Unfortu- culin fibres are encountered to varying degrees in nately the number of canine fibrosarcomas followed different parts of the tumour. Larger tumours often up over a long period was too small to allow conclu- show areas of central necrosis. Infiltrative growth of sions as to the real degree of malignancy of these tumour cells into lymphatic clefts and lymph and tumours. blood vessels takes place, and metastases occur. It 2. " Canine haemangiopericytoma" (fibrosarcoma seems possible that even the ill-defined pleomorphic with perithelioma-like structures, perithelioma, haem- sarcomas without any fibres are of fibroblastic angiosarcoma) (Fig. 4-6). Histologically, this tumour origin. is' characterized by spindle-shaped or fibrocyte- D. like cells arranged in curls, whorls, or finger- Equine sarcoid (Fig. 7, 8) print-like patterns. The nuclei are ovoid and hypo- Histologically, this tumour looks like a fibrosar- chromatic, and they have a distinct and finely-granu- coma. In contrast to papilloma, the mesodermal lated nuclear membrane. The typical feature of this proliferation is not only an adaptation to epidermal tumour is the onion-skin arrangement of tumour growth but the predominant part of the tumour. The cells around small vessels. The vessels have an open overlying epidermis is commonly ulcerated and sends or narrow lumen owing to hyalinization of the vessel deep pegs into the fibrous mass. Most frequently the wall. However, these structures are present only in tumour is found in the skin about the base of X - :qF N~ Fig. 1. Fibroma durum (dog). Fig. 2. Fibroma molle (dog). Fig. 3. Fibrosarcoma (dog). Fig. 4. " Canine haemangiopericytoma ". Fig. 5. " Canine haemangiopericytoma ". Fig. 6. " Canine haemangiopericytoma ", perivascular growth in necrotic area; Gomori's silver stain. Fig. 7. Equine sarcoid. Fig. 8. Equine sarcoid. ~~~~~~~~~~~~~~~~~~~~~~~~O 7, -I . Fig. 9. Cutaneous fibrous polyp (dog). Fig. 10. Calcinosis circumscripta (dog). Fig. 1 1. Lipoma (dog). Fig. 12. Liposarcoma (dog). Fig. 13. Leiomyoma (dog). Fig. 14. Rhabdomyosarcoma (dog). Fig.16 Malignant. haemangioendothe.Iom (dg) Fig. 15. Cavernous haemangioma (dog). Fig . 1 6. Malignant haemangioendothelioma (dog) . Fig. 17. Mast cell tumour; toluidine blue (dog). Mast cell tumour; toluidine blue (cat). .-Am 1 v hiticta F. 2 Fig. 19. Canine histiocytoma. Fig. 20. Canine histiocytoma. SOFr (MESENCHYMAL) TISSUES 109 the ears, but it can occur anywhere on the skin. The III. TUMOURS OF MUSCLE TISSUE initial lesion is warty (not horny), often multiple, and infiltrates later in dermis and subcutis. Recurrence A. Leiomyoma (Fig. 13) after excision is common, but metastases do not This benign tumour is composed of mature, non- occur. The tumour is autotransplantable to scarified striated muscle fibres with long match-like nuclei. skin and is presumably virus-induced. In many regions Collagen formation is present in varying degrees. about half the skin tumours in horses are sarcoids. Special stains (van Gieson's, Mallory's, azan) are helpful in differentiation from fibromas. The tumour E. Tumour-like lesions is rare in the skin but common in the female genital 1. Cutaneous fibrous polyp (Fig. 9). The cutaneous tract and in the alimentary tract. fibrous polyp is hairless and stalked or fungoid in shape. Its base consists of solid collagenous fibres B. Leiomyosarcoma with few cells. The covering epidermis shows super- This malignant tumour is less well differentiated ficial ulceration and long rete pegs. This lesion is very and more cellular than leiomyoma. The main histo- rare. logical features are: long hypochromatic and spindle- 2. Keloid and hyperplastic scar. Both lesions are shaped nuclei, multinuclear giant cells, mitotic figures, characterized by dense collagenous tissue with ex- and areas of necrosis. Special stains are helpful in tremely few nuclei and pronounced hyalinization of making a proper diagnosis. The tumour is rare in fibre fascicles that becomes particularly evident in animals. slides stained according to van Gieson's method. The C. Rhabdomyoma Clear differen- covering epidermis is hyperkeratotic. of long cells