Cytopathology of round cell and melanocytic tumors of cutaneous and subcutaneous origin in dogs Kaur Mandeep1, Gupta Kuldip1*, Mohindroo Jitender2, Singh Amarjit1 1Department of Veterinary Pathology, College of Veterinary Science, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana-141004, Punjab, India. 2Department of Veterinary Surgery and Radiology, College of Veterinary Science, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana-141004, Punjab, India. Address for Correspondence Dr Kuldip Gupta, Department of Veterinary Pathology, College of Veterinary Science, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana-141004, Punjab, India, E-mail: kgupta1968@gmail.com
Abstract The present study was conducted to study the occurrence of naturally occurring round cell tumors and melanocytic tumors in the cutaneous and subcutaneous tissues of dogs. Atotal of 60 cases of cutaneous and subcutaneous tumors were recorded from October, 2020 to March, 2021. Incidence of tumors was recorded with respect to age, sex, breed and body weight. The cytological findings were confirmed with histopathological findings, wherever tissue samples were available and special staining was also performed, wherever required. Out of 60 samples, 57 cases were of round cell tumors and three were of melanocytic tumors on the basis of cytology. Round cell tumors were further classified as lymphoma (23), TVT (22), Mast cell tumors (11) and histiocytic tumors (1). Interestingly, TVT was more common at extra- genital sites when compared togenitalia. The cytological and histopathological findings showed high correlation, sensitivity and positive predictive value for reliable diagnosis. From the study, it was concluded that cytology is effective in diagnosis of round and melanocytic tumors of cutaneous and subcutaneous origin in dogs. Top Keywords Canine, Cutaneous, Cytology, Melanocytic tumors, Round cell tumors, Subcutaneous tumor. Top |
Introduction Skin act as the most common location for the occurrence of tumors and about most of all the tumors in dogs are found on skin1. Round cell tumors of the skin contribute to a significant number to the skin tumors and consist of discrete cells that are round to oval in shape and cytological examination of these tumors by fine needle aspiration cytology gives definitive diagnosis2. Round cell tumors are highly exfoliative tumors and show good cellularity on the basis of cytological examination which is helpful in diagnosis3. Round cell tumors include lymphoma, transmissible venereal tumor, mast cell tumor, plasma cell and histiocytoma. Melanocytic tumors are tumors of melanocytes that produce melanin pigments. They are common in oral cavity and epidermal layer of skin4. |
The present study was undertaken to study the occurrence of round cell and melanocytic tumors in the cutaneous and subcutaneous tissues of dogs and describe their cytological and histopathological features. In addition, correlation between cytological and histopathological diagnosis of round cell and melanocytic tumors was carried out. |
Top Materials and Methods The study was conducted on 60 dogs presented to the Multi-Specialty Small Animal Hospital of the Department of Teaching Veterinary Clinical Complex, Guru Angad Dev Veterinary and Animal Sciences, Ludhiana during the time period of 1st October, 2020 to 31st March, 2021. Detailed history and signalment including age, breed, body weight, sex and clinical findings of dog in each case, presented with cutaneous and subcutaneous lesions was recorded. In addition, type of growth, size, shape, texture and superficial appearance of lesion were also recorded. Local metastasis was detected by palpation and distant metastasis was ascertained by radiography. The cytological smears collected by different methods viz. FNAB, swab method and impression smear from cases of cutaneous and subcutaneous tumor like lesions and submitted to the Centralized Clinical Diagnostic Laboratory were used for study. In addition, impression smears were also prepared from the tissue samples collected after surgical excision. The slides were prepared by different methods and were stained by Leishman’s staining method5. |
The cytological smears were analyzed and classified according to its characteristics of neoplastic cells and 57 cases of round cell tumors and three cases of melanocytic tumors were diagnosed. Tissue samples were collected in 10% NBF after excisional and incisional surgery, wherever possible. The samples were processed for paraffin sectioning and stained by routine H & E stain6. The slides were then analyzed and classified into different types of round cell tumors and melanocytic tumors according to its histological features. Wherever required, special staining was done with toluidine blue for demonstrating the mast cell granules7. The correlation between cytological and histopathological diagnosis was ascertained as per method described8. |
Top Results A total of 60 cases of cutaneous and subcutaneous tumors were presented during the course of study out which after initial cytological examination, 57 cases of round cell tumors and three cases of melanocytic tumors were diagnosed. The round cell tumors were further classified into lymphoma (23), TVT (22) and mast cell tumors (11), whereas, melanocytic tumors consisted of three cases of malignant melanoma (Table 1). |
Pathological changes in different tumors Round cells tumors Lymphoma Twenty three cases of lymphoma were diagnosed on the basis of cytological examination and histopathology could be done in one case only. Grossly in all the cases there was enlargement of different lymph nodes mainly involving the fore and hind limbs and in one case in the facial region. Cytological examination revealed high cellularity with monomorphic population of few well differentiated lymphocytes, along with many small to medium sized lymphoblasts having increased nuclear to cytoplasmic ratio, coarse chromatin and multiple nucleoli. In addition, lymphoglandular bodies and few mitotic figures were also observed (Fig. 1) Microscopic examination revealed proliferation of monomorphic population of large number of oval to round lymphoblast cells that altered the normal architecture of the lymph node (Fig. 2). Transmissible venereal tumor Twenty two cases of transmissible venereal tumor were diagnosed on the basis of cytological examination and histopathological examination could be done in two cases only. Out of the 22 cases, 13 cases were observed on extra-genital sites and nine cases were observed on the external genitalia of dogs. Among extra- genital cases, 10 cases were seen on skin as single to multiple, non-ulcerated nodular growths on different parts of the body, two cases in nasal cavity leading swelling of nasal cavity and epistaxis in one case was seen. Cytological examination revealed high cellularity with round to oval cells having round, central to eccentric nucleus, granular chromatin, single prominent nucleoli, mitotic figures, pale basophilic cytoplasm having characteristic clear, punctate and distinct cytoplasmic vacuoles. The vacuoles were even found in the extracellular location. Aspirates from the cutaneous lesions showed more vacuoles in the cytoplasm (Fig. 3). Microscopic examination revealed large, round to oval, or polyhedral cells arranged in the form of loose sheets and separated by thin connective tissue septa. The neoplastic cells hadindistinct outlines and clear cytoplasmic projections and poorly stained moderate amount of cytoplasm (Fig. 4). Mast cell tumor Eleven cases of mast cell tumor were diagnosed and further confirmed by histopathological examinationin 10 cases. Grossly, single to multiple, varying sized ulcerated and non-ulcerated growths were observed on ventral abdominal region, brisket region, scrotum, digits, paws, legs and ear. Cytological examination revealed large number of round cells having round to oval unstained nucleus with abundant pale cytoplasm containing numerous coarse, round, fine, purple granules. At times, the granules were seen obscuring the nucleus. At places the cytoplasm was densely stained due to granules and the nucleus appeared pale (Fig. 5). The granules were also prominent when stained by toluidine blue. Microscopic examination revealed round to polygonal having central to slightly eccentric nucleus with moderate amount, of pale cytoplasm containing pink to blue coloured granules. The neoplastic cells were arranged in the ribbon like pattern especially around the blood vessels (Fig. 6). In addition, few eosinophils were seen in between the neoplastic mast cells. Special staining with toluidine blue characteristically stained the metachromatic granules in the cytoplasm of mast cells (Fig. 7). Histiocytic tumor One case of histiocytoma was diagnosed by cytological examinationand was presented as multiple, hard, growth on neck region. Cytological examination showed large round to oval cells showing anisocytosis, anisokaryosis, karyomegaly, variation in nuclear to cytoplasmic ratio, indentations in nucleus with greyish blue cytoplasm. Tissue for histopathological examination was not submited in this case. Melanocytic tumors A total three cases of melanocytic tumors were presented clinically ulcerated and non-ulcerated growths around eyeball, oral cavity and one on the skin of the dorsal aspect of the body. Cytological examination revealed variable sized cells having coarse and clumped chromatin with multiple nucleoli and granular cytoplasm containing greenish black melanin pigment granules (Fig. 8). Tissue for histopathology was submitted in one case only and showed variable sized melanocytes having variable amount of melanin pigment arranged in cords. The neoplastic cells infiltrated and invaded the underlying dermis (Fig. 9). Correlation between cytological and histopathological findings In the present study out of the 57 cases of round cell tumors and three cases of melanocytic tumors samples, the histopathological examination was performed in 13 cases and one case respectively. In all the 14 cases, full concordance was found between cytological and histopathological diagnosis leading to 100 % correlation, sensitivity and positive predictive values. Top Discussion In the present study, out of the total 60 cases of cutaneous and subcutaneous tumors, 57 cases of round cell tumors and three cases of melanocytic tumors were diagnosed. Similarly, a high prevalence of round cell tumors followed by mammary gland tumors and epithelial tumors in skin of the dogs has been documented earlier9. On the contrary, a high incidence of mesenchymal tumors followed by epithelial and melanocytic tumors, in cutaneous and sub-cutaneous tissue of dogs have been reported10. |
The cytological and histopathological changes observed in different type of round cell and melanocytic tumors were almost similar to those reported by earlier workers. |
Earlier workers have similarly reported presence of large number of lymphobalsts with distinct cell borders, scanty basophilic cytoplasm, and high nuclear to cytoplasmic ratio on cytological examination of lymphoma11,12. In addition, similar microscopic findings of presence of uniform population of round to oval cells with prominent nucleoli and high nuclear to cytoplasmic ratio in the cases of lymphoma have been reported 13. Presence of large number of round to oval cells, having basophilic cytoplasm with many vacuoles and occasional mitotic figures in case of TVT on cytological examination have been observed14,15. On the other hand, sheets of pleomorphic round cells with eccentric nuclei with coarse chromatin have been documented in cases of TVT 16,17,18. The neoplastic cells were separated byconnective tissue strands on microscopic examination of TVT cases. Almost similar cytological findingsin mast cell tumors, characterized by round cells having pink to purplecolored granules in the cytoplasm of cellsthat often masked the nucleus have been observed19. Whereas, round to oval cells having eccentric nucleus with granules in the cytoplasm of the neoplastic mast cellsduring histological examination have been reported 20,21,22. In case of histiocytic tumors, early workers reported similar cytological features of round to oval, irregular shaped cells with round to oval nuclei withindentations and pale blue cytoplasm23,24. In cases of melanoma, presence of variable sized cells having round to oval nucleus, prominent nucleoli and green to black colored granules in the cytoplasm during cytological examination have been reported earlier 25 which are similar to our observations. Proliferation of melanocytes on microscopic examination that invaded deep into the dermis have been reported 26. In the present study, complete concordance was observed in cytological and histopathological diagnosis of round cells and melanocytic tumors. On the contrary, 71.4% agreement between cytologic and histologic diagnosis of cutaneous and subcutaneous tumors in general in dogs has been reported by earlier workers 27. |
From the study, it was concluded that cytology is an effective tool in diagnosis of round and melanocytic tumors of cutaneous and subcutaneous origin in dogs. |
Top Figures | Fig. 1.: FNAB from a lymph node showing mixed population of lymphocytes and small lymphoblasts. Along with a mitotic figure. Leishman’s stain ×100;
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| | Fig. 2.: Photomicrograph of lymph node showing monomorphic population of lymphoblasts that replaced normal tissue of the lymph node. H&E ×40;
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| | Fig. 3.: Impression smear from cutaneous nodules showing pleomorphic round cells having round cells with coarse chromatin, prominent nucleoli and vacuoles in the cytoplasm and outside the cells, suggestive of TVT, Leishman’s stain ×100;
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| | Fig. 4.: Photomicrograph from a case of eye TVT showing proliferation of round to oval neoplastic cells separated by connective tissue fibers. H&E ×20;
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| | Fig. 5.: Impression smear cytology from a case of mast cell tumor showing round nucleus with unstained nucleus and purple colored granules in the cytoplasm. Leishman’s stain ×100;
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| | Fig. 6.: Photomicrograph from a case of mast cell tumor showing round neoplastic cells with central to eccentric nucleus, pink cytoplasm containing blue colored granules. H&E ×40.
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| | Fig. 7.: Photomicrograph of a case of mast cell tumor showing metachromatic granules in cytoplasm of mast cells, toluidine blue x40;
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| | Fig. 8.: FNAB from a case of melanoma showing pleomorphic melanocytes having greenish-black colored melanin pigments in the cytoplasm. Leishman’s stain x100
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| | Fig. 9.: Photomicrograph from a case of melanoma showing proliferation of melanocytes invading the underlying tissue. H&E x10.
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Table Table 1.:
| | Type of Tumor | Cytological Diagnosis | Histopathological Diagnosis | | Round cell tumors (57) | Lymphoma (23) | Tissue for histopathology (1) | | | Lymphoma (1) | | Transmissible venereal tumor (22) | Tissue for histopathology (2) | | | Transmissible venereal tumor (2) | | Mast cell tumors (11) | Tissue for histopathology (10) | | | Mast cell tumors (10) | | Histiocytic tumor (1) | Tissue not submitted for histopathology (1) | | Melanocytic tumors (3) | Malignant melanoma (3) | Tissue for histopathology (1) | | | Malignant melanoma (1) |
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