Ординатура / Офтальмология / Английские материалы / Veterinary Ocular Pathology A Comparative Review_Dubielzig, Ketring, McLellan_2010

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Soft tissue sarcomas (Fig. 6.14)

Fibrosarcoma, high grade

There are eight canine cases and two feline cases in the COPLOW collection.

•The morphologic features useful in reaching a diagnosis of high-grade fibrosarcoma are as follows:

■Spindle-shaped cellular profile

■Extracellular collagen deposition

•These tumors should be graded in order to offer the most accurate prognosis, although our impression is that the orbit is an unfavorable location for a soft tissue sarcoma of any kind. The grading system of Barbara Powers is used by COPLOW and described below:

■Feature 1: Cellular differentiation, scored from 1 (tumor cells resemble normal tissue cells) to 3 (tumor cells are very anaplastic)

■Feature 2: Mitotic rate, expressed as number of mitotic figures per ten ×400 microscopic fields

–1 = 1 to 9

–2 = 10 to 19

–3 = More than 20

■Feature 3: Tumor necrosis

–1 = No necrosis

–2 = Less than 50% of the tissue is necrotic

–3 = More than 50% of the tissue is necrotic

Figure 6.11  Orbital fat prolapse (lipoma). (A) Beagle, 10 years old: lobulated subconjunctival masses are present at the nasal bulbar conjunctiva. Fine needle aspirate (FNA) confirmed fully-differentiated adipose tissue. (B) Opossum, adult: this is the right eye of a grossly overweight pet. A FNA confirmed normal adipose tissue in these subconjunctival masses. (C,D) Gross photographs showing orbital adipose tissue prolapsed forward, distorting the conjunctival profile.

■Total scores of 3 or 4 are grade 1 sarcomas, scores of 5 or 6 are grade 2 sarcomas, and scores of 7 to 9 are grade 3 sarcomas.

Morphologically low-grade, biologically high-grade fibrosarcoma of dogs (Fig. 6.15)

There are six cases of this tumor in the COPLOW collection, representing 0.15% of canine tumors in the collection.

•As the awkward name suggests, this tumor of the soft tissues of the canine skull defies the sarcoma grading scheme described above and needs to be carefully evaluated in order to make an accurate diagnosis

•These tumors have a breed predilection for the Golden Retriever, but can affect any breed of dog

•These are locally aggressive tumors of the skull and they carry a poor prognosis

•In order to accurately diagnose these challenging neoplasms, the following morphologic features must be taken into consideration:

■The hallmark feature of the morphologically low-grade, biologically high-grade sarcoma is abundant collagen within the neoplastic tissue

■By grading criteria, this is a grade 1 (low-grade) sarcoma for the following reasons:

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–The neoplastic cells either look exactly like native fibroblasts, or they have only mild cellular enlargement and large nuclei

–Mitoses and necrosis are never prominent in these tumors

■The challenge for the pathologist is to accurately distinguish between sarcoma and granulation tissue. The following features are helpful:

–Granulation tissue has a prominent vascular bed, with small blood vessels crossing at right angles to the direction of the spindle cells and collagen fibers; whereas sarcoma has fewer vessels and a more random distribution of blood vessels

■The challenge for the pathologist lies in answering the question of whether or not the lesion is neoplastic or reactive

–However, the clinician might already consider the lesion as being neoplastic, because of its aggressive and extensive behavior

–In these cases, it can be rewarding for pathologist to seek further input from the submitting clinician regarding their impression of the lesion’s biological behavior

■If the clinician is reluctant to determine that the lesion is neoplastic, particularly if it is early in the course of the disease, then the pathologist is faced with a difficult diagnostic decision.

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Anaplastic sarcoma (Fig. 6.16)

There are 10 cases of this orbital tumor in dogs and three cases of this tumor in cats in the COPLOW collection.

•These are, by definition, high-grade sarcomas, due to their lack of the features of tissue differentiation and failure to form any extracellular matrix, by which a more specific name can be given.

Liposarcoma (Fig. 6.17)

There are 10 cases of orbital liposarcomas in the COPLOW collection, all of them in dogs.

•There are two morphologic subtypes:

■Anaplastic tumors showing the following features:

–Cellular pleomorphism

–Multinucleate cells

–Scant extracellular matrix

–Lipid vacuoles in the cytoplasm

■Sharply delineated nodular masses with features of brown fat (hibernoma) showing the following features:

–Delineated nodules with little focal invasion

–Large monomorphic neoplastic cells with abundant delicately vacuolated cytoplasm

–A rich capillary vascular supply.

Extraskeletal osteosarcoma (Fig. 6.18)

There are seven cases of extraskeletal osteosarcoma of the orbit in dogs and four cases in cats in the COPLOW collection.

•The defining feature is the extracellular deposition of osteoid matrix in tumors that do not arise from bone

•Orbital osteosarcomas may or may not be directly connected to the orbital bone

•One case in a cat arose within the fibrous reaction surrounding an orbital prosthesis implanted after enucleation years before.

•These tumors can be either primary or secondary, but there are no reliable morphologic features to make a distinction

•Morphologic features of diagnostic importance are as follows:

■The morphologic hallmark of the tumor is the relationship between neoplastic cells and the red blood cells around them. In hemangiosarcoma the RBCs are within slit-like spaces defined by the tumor cells.

■The cellular profile can be extremely variable, ranging from primarily spindle cells, to polygonal cells with an epithelial appearance, to anaplastic forms.

Rhabdomyosarcoma (Fig. 6.19)

There are seven cases of orbital rhabdomyosarcoma in dogs in the COPLOW collection.

•Morphologic features of diagnostic significance include the following:

■Strap cells with abundant cytoplasm, parallel cell boundaries, and multiple lined up nuclei

■Cross striations in the cytoplasm

■Positive desmin, actin, myoglobin, or skeletal muscle actin labeling by immunohistochemistry

•Five of the seven cases are in dogs less than 3 years old.

Hemangiosarcoma

There are six cases of orbital hemangiosarcoma in dogs and three cases in cats in the COPLOW collection.

Tumors of the skull, extending to the orbit

Osteosarcoma (Fig. 6.20)

There are 10 cases of orbital osteosarcoma in dogs and three cases in cats in the COPLOW collection.

•In dogs, osteosarcoma of the axial skeleton, including the skull, is rarer than osteosarcoma of the appendicular skeleton, and less likely to spread by systemic metastasis. However, this distinction in biological behavior may be of limited clinical and prognostic significance because radical surgical excision by amputation is not an option

•Generally, osteosarcoma of the skull in dogs grows outwards from the skull

•The histological appearance can be that of a well-differentiated tumor suggesting a low-grade neoplasm in terms of biological

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behavior. However, aside from radical orbitectomy, which is a technically demanding procedure, there are few good surgical options. Radical excision, combined with adjunctive therapy may be of benefit in some patients.

Canine multilobular tumor of bone (chondroma rodens) (Fig. 6.21)

There are 12 cases of canine multilobular tumor of bone in the COPLOW collection.

•These are always tumors of the skull and often arise in suture lines between the flat bones of the skull

•They are locally effacing and aggressive, but they only rarely metastasize. Thus, local recurrence following excision is a problem but relatively long survival times may be achieved

•Morphologic features useful in establishing a diagnosis are as follows:

■As the name suggests, these tumors have a very characteristic lobulated pattern

–Each lobule is always surrounded by collagen rich spindle cells and not bone or cartilage matrix

–Within the nodule (or lobule), there is fully differentiated bone, cartilage, or both, with accompanying osteocytes and chondrocytes.

Feline skeletal osteochondromatosis (multiple cartilaginous exostoses) (Fig. 6.22)

•Affected cats develop one, or several, widely separated boney proliferations that grow outward from the skeleton, distorting the surrounding soft tissue

■Multifocal osteochondromatosis can occur in any bone as exostotic skeletal masses, and often involve the skull and orbit

•Unlike osteochondromatosis in young dogs, which occurs near growth plates and stops growing when the growth plate closes, the feline tumors continue to grow relentlessly after skeletal maturity. They therefore carry a much poorer prognosis

•Tumors often affect the skull and/or less frequently the long bones

•Tumors are made up of a mixture of well-differentiated bone and cartilage, often, but not always, with features that resemble a growth plate in the relationship between bone and cartilage

Figure 6.16  Orbital anaplastic sarcoma.

(A) Gross photograph of canine globe and orbital anaplastic sarcoma. (B) Photomicrograph of orbital anaplastic sarcoma showing poorly-differentiated neoplastic cells, including multinucleate giant cells (arrows).

•If incompletely excised, tumors can grow back with more malignant features

•A possible association with retroviral infection has been proposed but the causal relationship between naturally occurring FeLV infection and this form of hyperostosis remains unconvincing.

Other hyperostotic syndromes that may affect the orbit

•Craniomandibular osteopathy is characterized by irregular osseous proliferation of the skull bones in young dogs. Scottish, Cairn and West Highland white terriers are predisposed to this condition, that may affect orbital structures, leading to exophthalmos

•Idiopathic calvarial hyperostosis has been reported in young male Bull mastiffs. This rare syndrome of excessive bone proliferation affecting the calvarium may involve bones of the orbit, producing a mass effect or impinging on neurovascular structures

•Both of these conditions appear to be self-limiting when affected animals reach skeletal maturity.

Canine orbital meningioma (Figs 6.23, 6.24)

There are 60 cases of canine orbital meningioma in the COPLOW collection, representing 1.5% of canine tumors in the collection.

•This tumor shows distinctive morphology and biological behavior in the dog

•Characteristically, orbital meningiomas envelope the optic nerve outside the dura mater invading adipose tissue and loose connective tissues. Tumors form a cone around the optic nerve that conforms to the shape of the orbit

•Neoplastic cells are derived from the arachnoid cap cells which normally exist outside the dura mater near the globe, as discussed in Chapter 12

■Tumor cells may or may not extend into the dura mater, but they are always outside the dura because of the extradural origin

•These tumors are slow growing but hard to excise completely. Thus, local recurrence is relatively common. They can locally infiltrate into the optic foramen, and cranial vault and may displace or invade the brain, optic chiasm and contralateral

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optic nerve. Metastasis is uncommon, but has been reported in isolated cases

•Morphologic features useful in the diagnosis of canine orbital meningioma include:

■Tumors are solid near the optic nerve and show invasion between individual adipocytes, loose connective tissue, or myocytes away from the optic nerve

■The most common cellular profile of the neoplastic cells is meningotheliomatous, with a very epithelial-like appearance

–Neoplastic cells have abundant cytoplasm, polygonal shape, and form tight aggregates, all of which makes them appear as epithelial cells

–This tumor is often misdiagnosed as squamous cell carcinoma by the uninitiated pathologist

–When in doubt, canine orbital meningioma is generally vimentin-positive and cytokeratin negative on immunohistochemistry

■Less commonly, the neoplastic cells will be spindle cells with characteristic cellular whorls, more familiar as features of

Figure 6.20  Osteosarcoma of the skull. Gross photograph of a sectioned canine skull showing orbital osteosarcoma extending from the bony orbit.

meningioma to pathologists with more experience diagnosing intracranial meningiomas

■A very characteristic feature present in about 90% of canine orbital meningiomas, but never seen in intracranial meningioma, is the presence of foci of myxomatous, cartilaginous, or osseous metaplasia

–This can be a useful diagnostic feature if detected on diagnostic imaging.

Salivary or lacrimal gland adenocarcinomas (Fig. 6.25)

There are seven cases in dogs and two cases in cats within the COPLOW collection of solitary tumors arising from the zygomatic salivary gland or the lacrimal gland.

•Often their location within the orbit was considered to provide clues as to the likely tissue of origin, e.g. within the superior orbit is likely to be lacrimal in origin, rather than zygomatic salivary gland tumors which arise in the inferior orbit

•Adenocarcinoma of the gland of the third eyelid may also extend posteriorly into the orbit leading to exophthalmos

•The majority of salivary gland tumors are malignant but little is known about tumors of the lacrimal gland or zygomatic salivary gland specifically.

Canine orbital multilobular adenoma (Fig. 6.26)

There are 29 cases of canine orbital multilobular adenoma in the COPLOW collection, representing 0.65% of the total number of canine tumors in the collection.

•These tumors may present as either conjunctival swellings or as space-occupying orbital mass lesions

•The appearance at surgery is quite distinctive and the following are characteristic features:

■The lesions consist of soft, translucent lobules, each with a thin capsule, that are tenuously connected together. This feature makes them very hard to grasp and dissect. Because of this, excision is seldom complete unless enucleation or exenteration are performed

■Although benign, tumors often recur within 1–2 years of excision, and rare cases are bilateral