Peritoneal Mesothelioma in a Rabbit

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					             Veterinary Pathology Online

                                        Peritoneal Mesothelioma in a Rabbit
                                         C. A. Lichtensteiger and C. W. Leathers
                                                 Vet Pathol 1987 24: 464
                                          DOI: 10.1177/030098588702400518

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464                                                      Brief Communications

 sites of squamous cell carcinoma were zones of homogenized                              References
 collagen, which stained pale blue-gray with HE. Just below
                                                                  1 Hargis AM: A review of solar-induced lesions in do-
 and intermixed with the homogenized collagen was a zone
                                                                    mestic animals. Comp on Cont Educ 3(4):287-296, 1981
 of prominent, thick, wavy, gray elastic fibers. As in the first
                                                                  2 Hargis AM, Thomassen RW, Phemister RD: Chronic
case, there was no enlargement of regional lymph nodes and
                                                                    dermatosis and cutaneous squamous cell carcinoma in
no evidence of metastatic disease 1 year later.
                                                                    the beagle dog. Vet Pathol 14:218-228, 1977
   Solar elastosis has been attributed to either the alteration
                                                                  3 Jager JA, Scott D W The skin and appendages. In: Pa-
of collagen fibers, or of elastic fibers, or of both with incor-
                                                                    thology of Domestic Animals, ed. Jubb KVF, Kennedy
poration of amorphous granular material.’ One study of elas-
                                                                    PC, and Palmer N, 3rd ed., p. 509. Academic Press,
totic degeneration revealed an appearance of fine filaments
                                                                    Orlando, 1985
or granular material, or both around collagen fiber. This was
                                                                  4 Lever WF, Schaumberg-Lever G: Histopathology of the
thought to be due to collagen fibers splitting into microfibrils
                                                                    Skin. 6th ed., pp. 271-272. JB Lippincott Co, Philadel-
and granular material, with subsequent appearance of the
                                                                    phia, 1983
amorphous mass, or the formation of the amorphous mass
                                                                  5 Lloyd L C Epithelial tumours of the skin of sheep (tu-
directly through the gradual loss of collagen matrix with sub-
                                                                    mours of areas exposed to solar radiation). Br J Cancer
sequent confluence into future “elastotic fiber^."^
                                                                    15:780-789, 1961
   Suspected solar-associated squamous cell carcinoma has
                                                                  6 Madewell BR, Conroy JD, Odgluns EM: Sunlight-skin
been reported in equine non-pigmented conjuctiva, eyelid,
                                                                    cancer association in the dog: a report of three cases. J
and vulvar epithelium,’ and eyelid and conjunctiva.’ The
                                                                    Cutaneous Pathol8:434-443, 1981
equine nose, muzzle, and ear are less commonly recognized
                                                                  7 Mitchell RE: Chronic solar dermatosis: a light and elec-
sites for the development of suspected solar-associated squa-
                                                                    tron microscopic study of the dermis. J Invest Dermatol
mous cell carcinoma compared to the same sites on other
                                                                    48:203-220, 1967
domestic animals.
   The elastotic changes seen in these two equine cases mor-      8 Nakamura K, Johnson W C Ultraviolet-induced con-
                                                                    nective tissue changes in rat skin: a histopathologic and
phologically parallel solar-induced lesions in humans4 Hu-
                                                                    histochemical study. J Invest Dermatol51:253-258, 1968
man lesions usually arise in non-pigmented or lightly pig-
                                                                  9 Stevanovic D V Elastotic degeneration: a light and elec-
mented areas; squamous cell carcinomas with associated solar
                                                                    tron microscopic study. Br J Dermatol94:23-29, 1976
elastosis may locally recur following excision but have low
potential for regional metastases4 In contrast, de novo squa-    10 Uitto J, Ryhanen L, Abraham PA, Perejda AJ: Elastin
mous cell carcinomas, without evidence of solar elastosis,          in diseases. J Invest Dermatol79:1605-1685, 1982
arising in either pigmented or non-pigmented epithelium,
often have much greater metastatic potential. Solar elastosis, Request reprints from Dr. Gregory A. Campbell, Department
when observed in conjunction with squamous cell carcinoma of Comparative and Experimental Pathology, Box 5-145,
in non-pigmented epithelium of the horse, lends a more fa- JHMHC, University of Florida, Gainesville, FL 326 10 (USA).
vorable prognosis following the complete surgical excision
of the lesions.

Vet. Pathol. 24464-466 (1987)

                                      Peritoneal Mesothelioma in a Rabbit
                                    C. A. LICHTENSTEIGER C. W. LEATHERS

  Mesotheliomas are rare neoplasms. They have been re-                      atrophy. Several masses, up to 4 x 4 x 6 cm, were palpable
ported in various species, but occur more frequently in cattle,             in the caudal ventral abdomen. The rabbit was euthanized
rats, and man.6 Bovine mesotheliomas are often congenital,                  with an intraperitoneal overdose of dilute sodium pentobar-
in Fischer 344 rats, mesotheliomas of the tunica vaginalis                  bital.
are seen with aging and in dogs and man they are associated                    The peritoneal cavity contained about 500 ml of cloudy
with exposure to asbesto~.~ Surface mesothelial cells and sub-              red-yellow fluid. Several hundred tan-gray homogeneous
mesothelial stroma are neoplastic,l thus tumor appearance                   nodules 0.5 cm to 15 cm in diameter were scattered on ab-
vanes from epithelial to mesenchymal.l.9We report a spon-                   dominal serosa (Fig. 1); no normal mesentery or mesome-
taneous mesothelioma in a laboratory rabbit.                                trium was identifiable. Similar masses were attached to the
  A three-and-a-half-year-old female New Zealand White                      abdominal surface of the diaphragm, renal capsules, and
rabbit was noted by caretakers to have a distended abdomen.                 nearly-obscured ovaries and urinary bladder. Several addi-
The animal was alert, but had generalized skeletal muscle                   tional masses, attached by twisted pedicles to the serosa, were

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                                                        Brief Communications                                                          465

  Fig. 1. Rabbit abdominal cavity with widely disseminated neoplastic nodules.
  Fig. 2. Densely cellular area of neoplasm composed of mesenchymal cells. Bar = 75 pm.
  Fig. 3. Epithelial cell differentiation of neoplasm with papillae. Bar = 75 pm.
  Fig. 4. Cytoplasmic filaments with areas of dense condensations (dense bodies) adjacent to nucleus, a few mitochondria
and a lipid vacuole. Bar = 0.5 pm.
  Fig. 5. Intercellular microvilli, scant cytoplasm, and a few organelles. Bar = 0.5 pm.

gray-green to red-black (necrotic). No nodules were seen out-              of neoplastic cells that had epithelial, epithelioid, or mes-
side of the abdomen, and masses did not penetrate deeply                   enchymal features (Fig. 2). The mesenchymal cells were spin-
into viscera or muscle.                                                    dle-shaped with fusiform nuclei; epithelioid cells were round
   Formalin-fixed samples of most organs were paraffin-                    to polygonal with oval nuclei. Both cell types had scant eo-
embedded, sectioned, and stained with hematoxylin and eo-                  sinophilic cytoplasm and indistinct cell boundaries. In a few
sin (HE). Replicate sections of the tumor mass were stained                areas, the cells were less densely packed, had round to oval
with Masson’s trichrome, periodic acid-Schiff reaction, or                 nuclei, and abundant cytoplasm. In some areas, the epithelial
phosphotungstic acid-hematoxylin. Samples from perirenal                   cells were arranged in papillae (Fig. 3), in tubules, or with a
masses were deparaffinized and post-fixed in osmium te-                    myxomatous matrix. Occasional multinucleated (2 to 20+
troxide. Sections for electron microscopy were stained with                nuclei/cell) cells were seen. The mitotic index was low to
lead citrate and uranyl acetate.                                           moderate; 0 to 4 mitotic figures per 400 x field. Moderately
   Histologically, the masses were composed of dense sheets                vascular stroma was present, and a thin capsule surrounded

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466                                                       Brief Communications

islands of neoplastic cells and masses in the denser areas.                                                   References
Foci of necrosis were numerous, especially in masses greater                  1 Bolen JW, Hammar SP, McNutt MA: Reactive and
than 1.5 cm in diameter. Masses attached to viscera indented,                   neoplastic serosal tissue. A light-microscopic,ultrastruc-
but did not infiltrate the parenchyma. The masses on the                        tural, and immunocytochemical study. Am J Surg Pathol
diaphragm, however, did penetrate the muscle. Collagen in                       10:34-47, 1986
the tumor masses was scant, and muscle bands were not seen.                   2 Bolen JW, Thorning D: Mesotheliomas-a light- and
The uterus, ovaries, mammary glands, and intestinal tract                       electron-microscopicalstudy concerning histogenetic re-
were examined carefully; cystic endometrial hyperplasia was                     lationships between the epithelial and the mesenchymal
the only other histologic lesion.                                               variants. Am J Surg Pathol4:45 1-464, 1980
   Areas of dense fusiform cells and of less dense ovoid cells                3 Chabot JF, Beard D, Langlois AJ, Beard J W Meso-
were examined ultrastructurally. Cells from both areas had                      theliomas of peritoneum, epicardium, and pericardium
large nuclear to cytoplasmic ratios. Nuclei varied greatly in                   induced by strain MC29 avian leukosis virus. Cancer
size and were pleomorphic, often with indentations. Nuclei                      Res 30:1287-1308, 1970
contained mostly euchromatin with scant peripheral hetero-                    4 Dardick I, Srigley JR, McCaughey WTE, van Nostrand
chromatin. Most cells had a prominent nucleolus. Cytoplas-                      AWP, Ritchie AC: Ultrastructural aspects of the his-
mic organelles were minimal, with only a few mitochondria                       togenesis of diffuse and localized mesothelioma. Vir-
and rough endoplasmic reticulum profiles. Bundles of cyto-                      chows Archiv A 402:373-388, 1984
plasmic filaments, often perinuclear, were prominent. The                     5 Glickman LT, Domanski LM, Maguire TG, Dubielzig
filaments averaged 10.5 nm in diameter. Occasional junc-                        RR, Churg A Mesothelioma in pet dogs associated with
tional complexes were between cells, but no well-formed des-                    exposure of their owners to asbestos. Environ Res 32:
mosomes were seen. No surface microvilli were in the densely                    305-313, 1983
cellular areas, but numerous intercellular microvilli were in                 6 Gould DH: Mesotheliomas of the tunica vaginalis pro-
sparsely populated areas (Fig. 5). Minimal collagen and no                      pria and peritoneum in Fischer rats. Vet Pathol14:372-
distinct basement membranes were seen.                                          379, 1977
   Mesotheliomas have not been reported previously in rab-                    7 Shin ML, Firminger HI: Acute and chronic effects of
bits. Weisbroth’s list lo of reported rabbit neoplasms includes                 intraperitoneal injection of two types of asbestos in rats
two German case reports from the early 1900’s of a metastic                     with a study of the histopathogenesis and ultrastructure
abdominal sarcoma. We cannot rule out the possibility that                      of resulting mesotheliomas. Am J Pathol 70:291-3 14,
these neoplasms were mesotheliomas.                                              1973
   Reported mesotheliomas often have epithelial, mesenchy-                    8 Stewart SE: The polyoma virus (A). Adv Virus Res 7:
ma1 (sarcomatous), or biphasic characteristic^.^^^^^^^ Sparse                   61-90, 1960
microvilli, intercellular junctional complexes, and cytoplas-                 9 Suzuki Y, Churg J, Kannersein M: Ultrastructure of
mic filaments without prominent collagen fibrils, or myosin-                    human malignant diffuse mesothelioma. Am J Pathol
actin complexes are consistent with a mixed (biphasic) me-                      85241-262, 1976
sothelioma in the rabbit.                                                    10 Weisbroth SH: Neoplastic disease. In: The Biology of
   Mesotheliomas have been produced experimentally by as-                       the Laboratory Rabbit, ed. Weisbroth SH, Flatt RE, and
bestos in rats,’ MC29 avian leukosis virus in chicken^,^ and                    Kraus AL, pp. 331-375. Academic Press, Orlando, FL,
polyoma virus in Swiss mice.* This rabbit was not known to                         1974
have been exposed environmentally or experimentally to any
mesothelioma-inducing agent.                                                Request reprints from Dr. C. A. Lichtensteiger, Department
                                                                            of Veterinary Microbiology and Pathology, College of Vet-
                     Acknowledgement                                        erinary Medicine, Washington State University, Pullman,
  This work was supported in part by grant RR 070 19, Di-                   WA 99 164 (USA).
vision of Research Resources, National Institutes of Health.

Vet. Pathol. 24466-469 (1987)

                                               Arteriolosclerosis in a Cat
                                           F. C . MOHRAND J. L. CARPENTER

  Vascular disease limited to small arteries and arterioles is              another form of arterial disease in the cat, arteriolosclerosis.
uncommon in the cat. This condition may be systemic as in                   This form of arteriosclerosis is characterized by thickening
polyarteritis nodosa or localized as in feline dirofilariasis and           of the arteriolar walls due to muscular hyperplasia and hy-
medial hypertrophy of pulmonary arteries. We report here                    pertrophy of the media or hyalinization of the intima.5.9 In

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