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Brief communications 217
intracytoplasmic membrane-bound electron-dense neurose- References
cretory granules further suggests the presence of chief cells.
1. Capen CC: 1990, Tumors of the endocrine glands. In: Tumors
In the present study, the tumor cells have the histologic in domestic animals, ed. Moulton JE, 3rd ed., pp. 553-639. Uni-
and special staining pattern, immunohistochemical staining versity of California Press, Berkeley, CA.
properties, and ultrastructural features characteristic of neo- 2. Femandez Pascual JS: 1976, A new method for easy demon-
plasms of the chemodectoma group. The unusual location stration of argyrophil cells. Stain Technol 51:231-235.
of this tumor may be due to the widespread distribution of 3. Glenner GG, Grimley PM: 1974, Tumors of the extra-adrenal
chemoreceptor cells associated with the extra-adrenal tissue paraganglion system (including chemoreceptors). In: Atlas of tu-
of the paraganglionic system.3 This cow’s tumor may have mor pathology, 2nd ser. fast. 9, pp. 13-86. Armed Forces Institute
originated from the myocardial components of the intravagal of Pathology, Washington, DC.
paraganglia or the visceral autonomic paraganglionic cell 4. Kliewer KE, Wen D-R, Cancilla PA, et al.: 1989, Paraganglio-
groups associated with the myocardial vasculature and atria1 mas: assessment of prognosis by histologic, immunohistochem-
ical, and ultrastructural techniques. Hum Pathol 20:29-39.
septum of the heart.
5. Ladds PW, Daniels PW: 1975, Aortic body tumor in an ox. Aust
Acknowledgments. We thank Dr. B. G. Wiersma (Dairy- Vet J 51:43-44.
land Veterinary Service, Fond du Lac, WI) for submitting 6. Nordstoga K: 1966, Carotid body tumor in a cow. Vet Pathol
this case and Ms. Anne Slattery for performing the immu- 3:412-420.
nohistochemical stains. We are grateful for the cooperation 7. Smith HA, Jones TC, Hunt RD: 1972, Veterinary pathology,
and histotechnologic support provided by Ms. Susan Samuel- 4th ed., pp. 254-255. Lea and Febiger, Philadelphia, PA.
sen and Ms. Beth Byrne and for the photographic assistance 8. Warren WH, Caldarelli DD, Javid H, et al.: 1985, Neuroen-
provided by Mr. Craig Radi. docrine markers in paragangliomas of the head and neck. Ann
Otol Rhinol Laryngol 94:555-559.
Sources and manufacturers 9. Yates WDG, Mills JHL, Bryant LP: 1981, Aortic body tumor
in a cow. Can Vet J 22: 19-20.
a. Dako Corp., Carpinteria, CA.
b. Strept Avidin Kit, Biogenex Laboratories, San Ramon, CA.
J Vet Diagn Invest 4:217-220 (1992)
Sclerosing peritoneal mesothelioma in a dog evaluated by
electron microscopy and immunoperoxidase techniques
Polly Schoning, Candace E. Layton, William D. Fortney,
Lloyd H. Willard, J. E. Cook
Mesotheliomas are rare neoplasms.4 They arise from the erate numbers of hypersegmented neutrophils, and moderate
serous lining of the thoracic, abdominal, and/or pericardial numbers of erythrocytes. Also seen were occasional clusters
cavities.5 Two histologic patterns are recognized; 1 is pre- and rosettes of very basophilic cells containing large nuclei
dominately fibrous, with fibrosarcoma as a differential di- with prominent nucleoli. The opinion rendered was probable
agnosis, and 1 is predominately epithelial, with adenocar- neoplasia, mesothelioma or carcinoma. Cytology of aspi-
cinoma as a differential diagnosis5 In dogs and humans, most rate of the abdominal muscle masses was undiagnostic.
mesotheliomas are in the pleural cavity and tend to be epi-
thelial.8,12 Mesotheliomas produced experimentally in ani-
mals (rat, hamster, mouse, guinea pig, rabbit, dog, rhesus
monkey, and baboon), however, are usually fibrous or sar-
A 6-year-old male German shepherd was admitted to the
Kansas State University Veterinary Medical Center with a
history of weight loss, anorexia, and abdominal distension.
Upon examination, masses were palpated in the abdominal
muscles, lateral to the prepuce, and in the abdominal cavity.
Serosanguinous fluid was aspirated from the abdominal cav-
ity. Cytology revealed many vacuolated macrophages, mod-
From the Departments of Pathology (Schoning, Willard, Cook)
and Clinical Sciences (Layton, Fortney), College of Veterinary Med-
icine, Kansas State University, Manhattan, KS 66506. Figure 1. Sclerosing peritoneal mesothelioma of a dog, showing
Received for publication August 28, 1991. the thickened, constricted, convoluted intestines.
Figure 2. Cross section of a convoluted mass of formalin-fixed
small intestine from a dog, showing the thick, adherent mesentery.
Abdominal radiographs and sonographs revealed perito-
neal effusion, gas-filled small and large intestines, and pros-
tatic cysts. A complete blood count and serum chemistry
profile were unremarkable. Exploratory surgery revealed a
constricted convoluted mass of small intestines. The con-
dition was determined to be inoperable, and the dog was Figure 4. Fibroblasts are the predominant cells in this canine
mesothelioma. Note the large nucleus/cytoplasm ratio, abundant
rER, and collagen fibers. Bar = 2 µm.
The major gross finding was the mass of contorted intes-
tines (Figs. 1, 2). The intestines were firm, and the serosa
was thickened but smooth. After removal, the intestinal tract the thoracic cavity, compression atelectasis, and a 4-cm blood-
could not be stretched out or opened without difficulty be- filled cyst in the prostate.
cause of the fusion of the loops by the thickened serosa. Firm Microscopically, the intestinal serosa and masses in the
masses extended from the peritoneum into the ventral ab- abdominal musculature were neoplastic. The serosal surface
dominal muscles, lateral to the prepuce. Other gross findings of the entire small intestine was composed of a thick layer
included approximately 1 liter of serosanguineous fluid in of mainly fibrous connective tissue interspersed with a few
“large cells.” This tissue completely surrounded the intestine
and was the same thickness as the muscular wall of the in-
testine. Two cell types were identified (Fig. 3). The first cell
type, which was more numerous, had characteristics of fi-
broblasts. Cells were densely packed and spindle shaped, with
indistinct borders and pink cytoplasm. Nuclei were large,
usually oval, and clear, with occasional small nucleoli. In
most areas, mitoses were few (less than 2/high power field).
The other cell type was scarce and occurred individually,
interspersed between the fibroblasts. Cells were large and
round, with distinct borders and pink-orange cytoplasm. Nu-
clei were large and pleomorphic, with large nucleoli. The
neoplasms from the 2 sites, serosa and muscle, were similar
except the serosal neoplasm had fewer “large cells” and more
collagen. Microscopic changes in other organs were limited
to a mild chronic glomerulonephritis and cystic hyperplasia
of the prostate.
Sections of neoplasm were deparaffinized and stained, us-
Figure 3. Photomicrograph of a section of sclerosing peritoneal ing an immunoperoxidase technique. Antibody to low mo-
mesothelioma from a dog. Most of the cells are fibroblasts with lecular weight cytokeratin was used to detect keratin, which
mesothelial cells (arrows) interspersed. HE stain. 225 x . is present in mesothelial and epithelial cells but not in fibro-
Brief communications 219
Figure 5. Mesothelial cells from a canine mesothelioma showing
microvilli, large irregular nuclei, well-formed rER, and intercellular
junctions. Bar = 2 µm.
Figure 6. Junction between 2 mesothelial cells from a canine
peritoneal mesothelioma, showing desmosome-like structures. Bar
blasts. The large cells stained positive for keratin, whereas = 0.25 µm.
the fibroblasts remained unstained.
Formalin-fixed tissue was embedded, sectioned, and stained
for transmission electron microscopy. Most of the cells were because it is more common than neoplasia. Furthermore,
fibroblasts, characterized as elongate, with the nucleus form- this case clinically resembled 2 previous cases of sclerosing
ing the largest part of the cell’s diameter (Fig. 4). The cyto- peritonitis (Fortney, Layton, personal observation) and cases
plasm contained abundant rough endoplasmic reticulum reported by others.2 Peritonitis was eliminated as a diagnosis
(rER); the surrounding matrix contained collagen fibers. Oth- because of the uniformity of the fibrosing lesion and the
er cells (Fig. 5) had characteristics of mesothelial cells; they absence of inflammation. Progressive systemic sclerosis1,9,10
were large and round, with a few surface microvilli and in- has been reported in dogs and humans and is characterized
tercellular junctions (Fig. 6). The nuclei were large and very by fibrosis within the muscular wall and the presence of
irregular in shape and had large nucleoli. The cytoplasm had mononuclear cells. In the present case, fibrosis was limited
well developed rER, microfilaments, glycogen granules, and to the serosa, and there were no inflammatory cells.
occasional vacuoles. Neither of the 2 cell types looked ma- Fibrosarcoma remained a valid differential diagnosis be-
lignant; 1 resembled fibroblasts, the other resembled epithe- cause of the large number of fibroblasts recognized micro-
lial cells. scopically. However, the neoplasm did not have the char-
Although mesotheliomas are rare, they have been reported acteristics of a fibrosarcoma. It did not invade the intestinal
in all of the common domestic animals.4 Most canine mes- wall, had a low mitotic incidence, had not metastasized, and
otheliomas are in the pleural cavity and the epithelial form, contained cells that were epithelial. Although the neoplasm
which is characterized grossly as multiple nodules of various invaded the abdominal musculature, it communicated with,
sizes and microscopically as papillary projections composed or extended from, the peritoneum.
of a core of connective tissue covered with large round meso- Gross differentiation of epithelial mesotheliomas from ad-
thelial cells. However, peritoneal mesotheliomas,3,6,7 includ- enocarcinomas is difficult because both appear as nodules
ing sclerosing ones, have been reported in the dog. Meso- covering serosal surfaces. Both mesothelial cells and carci-
theliomas are classified as benign or malignant. Reports of noma cells stain for cytokeratin; therefore, additional im-
metastasis are rare,8,11 but compression and constriction of munoperoxidase techniques, which are often not helpful,
organs surrounded by mesotheliomas and transplantation of would be needed to separate the 2 tumor types. In this case,
neoplastic cells can result in death. adenocarcinoma was eliminated as a diagnosis because of
Differential diagnoses of this case included chronic peri- the neoplasm’s gross appearance and the absence of primary
tonitis, progressive systemic sclerosis, fibrosarcoma, ade- neoplasia in any organ that could act as a source, such as
nocarcinoma, and mesothelioma. Chronic peritonitis was prostate.
initially considered because of the sanguineous effusion and Sclerosing mesothelioma was coined3 to describe a meso-
220 Brief communications
thelioma that is characterized by the presence of fibroblasts Acknowledgment. This report is contribution number 91-
and collagen. A sclerosing mesothelioma is probably a vari- 514-J from the Kansas Agricultural Experiment Station.
ant of fibrous or sarcomatous mesothelioma, with the pres-
ence of numerous normal fibroblasts. Grossly and micro- References
scopically, this case was similar to sclerosing mesothelioma 1. Arrick RH, Kleine LJ: 1978, Intestinal pseudoobstruction in a
reported previously in 5 dogs.3 In that report, 3 of the 5 dogs dog. J Am Vet Med Assoc 172:1201-1205.
were German shepherds and all were males. All 5 had a 2. Boothe HW, Lay JC, Moreland IU: 1991, Sclerosing encap-
serosanguineous effusion in the abdominal cavity, and 3 had sulating peritonitis in three dogs. J Am Vet Med ASSOC 198:
effusion in the pleural cavity, All 5 dogs had abnormalities 267-270.
of the prostate. In another report of 2 dogs with sclerosing 3. Dubielzig RR: 1977, Sclerosing mesothelioma in five dogs. J
mesothelioma,6 both were male German shepherds with pro- Am Anim Hosp Assoc 15:745-748.
4. Head KW: 1990, Mesothelioma, tumors of the alimentary tract.
static hypertrophy. These findings strongly suggest a corre-
In: Tumors in domestic animals, ed. Moulton JE, 3rd ed., pp.
lation in male German shepherds between prostatic hyper- 422-435. University of California Press, Berkeley, CA.
trophy and sclerosing mesothelioma. 5. Julian RJ: 1985, The peritoneum, retroperitoneum, and mes-
Microscopically, Fig. 3 closely resembles photomicro- entery. In: Pathology of domestic animals, eds. Jubb KVF, Ken-
graphs in the previous reports.3,6 This case differs from those, nedy PC, Palmer N, 3rd ed., pp. 330-341. Academic Press, New
however, in that cells were not seen lining the serosal surface, York, NY.
cysts, or in large foci. However, more mesothelial cells were 6. Loupal G: 1987, Sclerosing mesothelioma in the dog. [In Ger-
seen on the serosal surface with immunoperoxidase staining man.] J. Vet Med Ser A 34:405-414.
than were recognized with hematoxylin and eosin. This lesion 7. Marchiori MI, Lucia WF, Coelho HE, et al.: 1986, Peritoneal
may have been of longer duration, with more fibrosis and mesothelioma in a dog. [In Portuguese.] Arq Bras Med Vet
fewer mesothelial cells. Zootec 38: 159-166.
8. McCaughey WTE, Kannerstein M, Churg J: 1985, Tumors and
Electron microscopy is seldom helpful in differentiating pseudotumors of the serous membranes. In: Atlas of tumor
adenocarcinomas from mesotheliomas because both are pathology, eds. Hartmann WH, Sobin LH, 2nd ser., fast. 20,
composed of epithelial cells. Furthermore, mesothelial cells pp. 1-124. Armed Forces Institute of Pathology, Washington,
in mesotheliomas are often normal rather than anaplastic.13 DC.
Ultrastructurally, mesothelial cells are characterized by long 9. Moore R, Carpenter J: 1984, Intestinal sclerosis with pseudo-
surface microvilli, desmosomes, microfilaments, well-devel- obstruction in three dogs. J Am Vet Med Assoc 184:830-833.
oped rER, and sometimes vacuoles. In this dog, microvilli 10. Schuffler MD, Rohrmann CA, Chaffee RG, et al.: 198 1, Chron-
were short and few, probably because the cells were inter- ic intestinal pseudo-obstruction. Medicine 60: 173196.
spersed between fibroblasts rather than in their usual surface 11. Smith DA, Hill FWG: 1989, Metastatic malignant mesothe-
location. The intercellular junctions contained desmosomes, lioma in a dog. J Comp Pathol 100:97-101.
12. Thrall DE, Goldschmidt MH: 1978, Mesothelioma in the dog:
which were not classical but were similar to those previously six case reports. J Am Vet Radiol Soc 19: 107-115.
illustrated.6 13. Trigo FJ, Morrison WB, Breeze RG: 1981, An ultrastructural
This case was challenging because of the several logical study of canine mesothelioma. J Comp Pathol 91:531-537.
differential diagnoses and illustrates the need and benefit of
using supportive diagnostic techniques.
J Vet Diagn Invest 4:220-222 (1992)
Scoliosis and hydrocephalus in an ovine fetus
infected with Toxoplasma gondii
Leslie W. Woods, Mark L. Anderson
Toxoplasma gondii causes abortion, fetal mummification, fetal lamb with T. gondii infection and concurrent infection
and perinatal death in sheep and other livestock, but there with Escherichia coli.
are no documented reports of hydrocephalus or skeletal de- Two full-term twin ovine fetuses were submitted to the
formities in animals associated with congenital infection.5,10 California Veterinary Diagnostic Laboratory for necropsy.
Congenital infection with T. gondii can cause chorioretinitis, Both fetuses were dead on delivery by cesarian section, which
hydrocephalus, microcephalus, and mental retardation in hu- was performed on the ewe after the amniotic sac failed to
mans.5 This is a report of scoliosis and hydrocephalus in a rupture and oxytocin therapy failed to induce cervical dila-
From the California Veterinary Diagnostic Laboratory System The ewe was 1 of 3 registered Suffolk maiden ewes and 1
University of California, Davis, CA 95617- 1770. ram lamb (average weight of 82 kg) that were purchased 6
Received for publication August 29, 1990. months previously and placed in the same pasture as a