Abdominal mesothelioma in a dog

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					                     Abdominal mesothelioma in                                          a   dog
                                  Douglas C. Forbes, Brendan R. Matthews

 A    12-year-old intact female Chihuahua weighing
 Papproximately 3 kg was presented because of
gradual abdominal enlargement. Aside from some
weight loss, the owner claimed that the dog was
healthy. On physical examination it       was   bright   and
active. The abdomen was markedly distended and
radiography revealed a fluid density throughout.
Needle aspiration of the abdomen produced straw-
colored fluid with  a specific gravity of 1.025 and a total

protein of 64 g/L. The sediment contained many
epithelioid cells. At this point, we suspected neoplasia
and performed an exploratory laparotomy. Numerous
discrete, small (3-8 mm), white nodular masses were
found over all serosal surfaces in the abdomen. About
400 mL of fluid were removed and samples of the
tumor were collected from the surface of the bowel
and abdominal cavity for histopathalogical studies.
An ovariohysterectomy was performed and recovery
was   uneventful.

                                                                                                             . .:   mw

                                                               Figure 2. Gross appearance of mesothelioma on necropsy.
                                                               Note the numerous, discrete, raised lesions on the surface
                                                               of the small intestine and on the abdominal wall.
                                                                  Histological studies (Dr. Sally Lester, Central Lab-
                                                               oratory for Veterinarians, Langley, British Columbia)
                                                               demonstrated a most unusual proliferation of mesothelial
                                                               cells with very little proliferation of fibrous tissue
                                                               (Figure 1). The cells were thrown into numerous
                                                               papilliform projections around cores of dense fibrous
                                                               tissue. The cells were not associated with any inflam-
                                                               matory reaction. They had a moderate mitotic index.
                                                                  The dog did very well over the next three-and-one-
                                                               half years. About every four months, the owner pre-
                                                               sented the dog to have the abdomen drained due to
                                                               the gradual accumulation of fluid which made the dog
                                                               uncomfortable and dyspneic. Rapid aspiration was
                                                               achieved using a suction pump and an 18 gauge needle
                                                               inserted through a surgically prepared area of the
                                                               ventral abdomen. Anesthesia was not required.
                                                                  Following aspiration the owner reported immediate
                                                               improvement of the dog's condition; during most of
                                                               the treatment period, weight and general good health
                                                               were maintained. Euthanasia was performed when the
                                                               dog began to have severe dyspnea and loss of weight
                                                               during month 42 of therapy. On necropsy the tumor
                                                               distribution pattern appeared almost the same as it had
                                                               during the laparotomy 42 months earlier (Figure 2).
                                                               The histological appearance of the mesothelioma was
                                                               also similar. There were no abnormal gross findings
Figure 1. Well differentiated mesothelial cells which are      in the thorax.
proliferating into papilliform projections. H&E.                  Mesotheliomas are quire rare in dogs. They have
Can Vet J 1991; 32: 176-177                                    also been reported in man, horses, cattle, and cats
                                                               (1-5). These tumors can be composed of epithelioid
Central Animal Hospital, 104 Tranquille Road, Kamloops,        or mesenchymal components or both (6). The meso-
British Columbia V2B 3E6.                                      thelioma in this case consisted of very well differen-
176                                                                                    Can Vet J Volume 32, March 1991
tiated cells indistinguishable from epithelial cells. The   unknown but there appears to be a direct relationship
absence of adhesions can be attributed to the lack of       between chronic asbestos inhalation and the incidence
exposed fibrous cells, which is characteristic of the       of pleural mesotheliomas in humans (3).
mesenchymal form. These tumors spread by the                   A total of 3377 mL of ascitic fluid was removed
seeding of papilliform growths which are shed from          from this small dog over a period of 42 months. This
the expanding surface of the neoplasm (1,7). This           reflects a total protein loss of about 48 g or about 1.2 g
accounts for the generalized spreading of the tumor         per month. We believe that this minor protein loss was
throughout the serosal surfaces of the abdomen but          an important reason why this patient tolerated the
failure to spread across the diaphragm and onto the         aspiration therapy over a fairly long period of time.
pleural surfaces of the thoracic cavity. The straw-            Rapid aspiration of ascitic fluid by suction pump
colored fluid was a result of serous effusion from,         was a simple and seemingly effective technique in this
and/or obstruction of lymphatic drainage by, the            patient. Experienced clinicians express caution about
neoplasm (5,7,9). This fluid would be classified as a       the removal of ascitic fluid unless it is made necessary
modified transudate (8). Dyspnea was attributed to the      by apparent discomfort or dyspnea (7). Complications
build-up of fluid causing an increase in abdominal          of abdominal paracentesis can include hypovolemia,
pressure on the diaphragm, making inspiration dif-          hypoalbuminemia, and peritonitis (10), none of which
ficult. Because of questionable owner compliance, no        occurred in this patient.                              cvJ
attempt was made to treat this dog with diuretics or
a salt-restricted diet.
                                                             1. Jubb KVF, Kennedy PC, Palmer N, eds. Pathology of Domestic
Complications of abdominal paracentesis can                     Animals. 3rd ed. Vol 2. Toronto: Academic Press, 1985:
include hypovolemia, hypoalbuminemia, and                       339-340.
                                                             2. Vetweber JG, Cole DE, Quadri SK, Schmidt MK. Premature
   peritonitis, none of which occurred in                       mammary development in a heifer with abdominal
                  this patient                                  mesothelioma. J Am Vet Med Assoc 1986; 189: 804-805.
                                                             3. Magnusson RA, Veit HP. Mesothelioma in a calf. J Am Vet
                                                                Med Assoc 1987; 191: 233-234.
   In one study, the mesenchymal form of this tumor          4. Schaer MS, Meyer D. Benign peritoneal mesothelioma, hyperthy-
                                                                roidism, nonsuppurative hepatitis and chronic disseminated
in dogs was described as sclerosing mesothelioma, a             intravascular coagulation in a cat. J Am Anim Hosp Assoc 1988;
form that has a tendency to spread and create thick,            24: 195-202.
fibrous adhesions throughout the serosal surfaces of         5. Tilley LP, Owens MJ, Wilkins RJ, Patnaik AK. Pericardial
the abdomen. These dogs showed severe distress and              mesothelioma with effusion in a cat. J Am Anim Hosp Assoc
                                                                1975; 11: 60-65.
were usually diagnosed as having generalized                 6. Suter PF, Zinkl JG. Mediastinal, pleural and extrapleural
peritonitis (9).                                                thoracic diseases. In: Ettinger SJ, ed. Textbook of Veterinary
   Most mesotheliomas are classified as malignant               Internal Medicine. 2nd ed. Philadelphia: WB Saunders, 1983:
because of their tendency to spread and implant.                877-878.
A benign form has been demonstrated in a cat (4). The        7. Thomson RG. General Veterinary Pathology. Philadelphia:
                                                                WB Saunders, 1978: 355.
characteristics were similar to a human disorder which       8. Ettinger SJ. Ascites, peritonitis and other causes of abdominal
has been described as benign mesothelial proliferation          enlargement. In: Ettinger SJ, ed. Textbook of Veterinary Inter-
with effusion.                                                  nal Medicine. 2nd ed. Philadelphia: WB Saunders, 1983: 127.
   Most mesotheliomas occur in adult or aged animals,        9. Dubielzig RR. Sclerosing mesothelioma in five dogs. J Am Anim
                                                                Hosp Assoc 1979; 15: 745-748.
with the exception of cattle. In this species, the tumor    10. Hardy RM. Diseases of the liver. In: Ettinger SJ, ed. Textbook
has been reported in calves, some as young as ten days          of Veterinary Internal Medicine. 2nd ed. Philadelphia: WB
of age (3). The etiology of mesotheliomas is still              Saunders, 1983: 1428.

     0>jMA   ACL,                 Winnipeg '91              c>IMA ACV
                      43rd Annual Convention of the CVMA
                          43e Congrbs annuel de l'ACV
                       July 7-10, 199117 au 10 juillet 1991      IPEG"
    Look for your personal invitation to Winnipeg '91,      Vous trouverez dans l'enveloppe du present
    the annual convention of the Canadian Veterinary        numero de la Revue vet6rinaire canadienne votre
    Medical Association, in the envelope of this Cana-      invitation personnelle a Winnipeg '91, c.-A-d. le
    dian VeterinaryJoumal. The special 24-page sup-         congres annuel de l'Association canadienne des
    plement to this issue contains the convention           v6t6rinaires. Le supplement special de 24 pages
    program and registration guide. More copies are         contient le programme du congres et un guide
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                                                            plaires supplementaires en telephonant a I'ACV,
                                                            au (613)236-1162.

Can Vet J Volume 32, March 1991                                                                                           177

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