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).
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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 with tiation from true neoplasms such as fibromas is This benign tumour is composed fibres can be shown by proper vesicular hypochromatic nuclei in syncytial forma- possible if elastic easy to demon- staining methods; true neoplasms of connective tis- tion. Cross-striations are not always elastic fibres. strate. With azan, the cytoplasm is stained yellow; sue do not show with Mallory's stain, bright red. Glycogen-contain- 3. Calcinosis circumscripta (calcium gout, apocrine ing cells are frequent and show a vacuolated pattern. cystic calcinosis (Fig. 10). Central deposits of coarse The tumour is rare in animals. basophilic granules are surrounded mainly by ma- crophages and giant cells. This is a granulomatous D. Rhabdomyosarcoma (Fig. 14) lesion common in young dogs of large breeds and it Well-differentiated and pleomorphic types have is most frequent in the skin of the limbs, especially been described. Often cross-striations are not visible. the subcutis of the footpads, over bony prominences, This malignant tumour is very rare in animals. but also occasionally in the oral cavity, e.g., the tongue. IV. TUMOURS OF BLOOD AND LYMPH VESSELS A. Cavernous haemangioma (Fig. 15) II. TUMOURS OF FAT TISSUE Typical histological features of this benign tumour A. Lipoma (Fig. 11) are cavities lined by a monolayer of endothelium and This benign tumour is composed of mature fat separated by varying amounts of fibrous stroma. cells. Sometimes there are broad bands of dense Very frequently, especially after traumatic insults, connective tissue between the cells. In large lipomas, thrombi in various stages of organization are en- areas of necrosis and dystrophic calcification are countered. quite common. Myxoid changes may occur. Lipomas have a predilection for the thoracic region and thighs B. Malignanthaemangioendothelioma (angiosarcoma) and are more common in bitches. (Fig. 16) These highly malignant tumours have a tendency B. Liposarcoma (Fig. 12) towards solid growth of atypical, polymorphic endo- This malignant tumour is rich in hypochromatic, thelial cells and therefore they show a certain simi- ovoid or round nuclei and mitotic figures. Well- larity to fibrosarcomas. The presence of erythrocytes differentiated and pleomorphic types occur. The within spaces formed by malignant endothelial cells, latter are more malignant and metastasize more which always exist in at least some areas of the frequently. tumour, establishes the diagnosis. Mitotic figures are
9 110 E. WEISS numerous. Metastases in various organs are com- oval, polygonal, or elongated and have oval nuclei. mon. Malignant haemangioendothelioma is not an The cytoplasm appears pale red and slightly granular undifferentiated anaplastic form of cavernous haem- in haemotoxylin and eosin sections. Some tumours angioma, but a neoplasm sui generis. show very poor granule formation, and diagnosis is helped by staining with toluidine blue. In less well C. Glomus tumour differentiated mast cell tumours, bizarre cells-which Epithelioid, angioma-like, and neuroma-like types may be multinucleated-may occur. Metachromasia can be distinguished in man. The cells show a pink of granules is often slight. cytoplasm and large oval hypochromatic nuclei, and Mast cell tumours are the most common mesen- hence are similar to epithelioid cells. In angioma-like chymal cutaneous neoplasms of dogs and occur very types, the tumour cells are arranged around blood frequently in the boxer breed. They occur also in cats vessels consisting only of endothelium, and, at the and less frequently in other species. Mast cell tumours earliest stages, resemble normal glomus structures. may be multifocal, and recurrences and metastases These benign tumours are very rare in animals. commonly lead to systemic involvement (malignant Neuroma-like types have not yet been recognized in mastocytosis).a dogs and there is some doubt whether the other forms of glomus tumour occur in this species. VII. CANINE HISTIOCYTOMA D. Lymphangioma The cells of this benign tumour (Fig. 19, 20) are This benign and rare tumour is composed of lymph relatively small and seem to form a syncytium. The vessels forming capillary, cavernous, or cystic nuclei are mostly round and hypochromatic. Mitotic tumours. Congenital lymphangiomas (malforma- figures and regressive changes are common. The tions) are known in animals as well as in man. tumour is frequent in young dogs, especially on the head and extremities. Ordinarily, spontaneous re- E. Lymphangiosarcoma (malignant lymphangioendo- gression occurs. thelioma) This malignant tumour is extremely rare in ani- VIII. RETICULOSARCOMA (CUTANEOUS RETICULOSIS) mals. These malignant tumours, which may be single or F. Tumour-like lesions multiple, are szen in old dogs. They resemble histiocy- tomas (VII), but the nuclei of the tumour cells are Varicosis and ectasia of scrotal veins can be con- more polymorphic and hyperchromatic. Probably sidered as tumour-like lesions of blood-vessels. They these tumours are special forms of lymphosarcoma.a show some similarities with angiokeratoma (Mibelli) of man. Especially ectasia of veins can be confused MISCELLANEOUS TUMOURS with cavernous haemangioma. The typical localiza- IX. tion of the lesions in the scrotum is an important Certain tumours classified as mainly affecting criterion for differential diagnosis. other body sites or systems sometimes involve the mesenchymal tissues of the skin. Lymphosarcoma, V. MESENCHYMAL TUMOURS OF PERIPHERAL NERVES especially in cattle, is sometimes localized in the (See Part V. Tumours of the nervous system, skin.a Canine transmissible venereal tumour, al- page 53.) though most commonly located on the genitalia, in some cases occurs in the skin (this tumour will be VI. MAST CELL TUMOUR (MASTOCYTOMA) included in the classification of the male genital system, to be published later). This malignant tumour (Fig. 17, 18) is composed of mast cells showing a wide range of granulation a See Part II. Neoplastic diseases of the haematopoietic both among and within cases. The cells are round, and lymphoid tissues, page 21.