May, 2000

Background   Physical Examination   Neurology Examination Results   Tests Performed   Summary

Background

This dog was seen at the Veterinary Medical Teaching Hospital, University of California Davis. We are grateful for the skillful participation by the Radiology Service and Clinical Laboratories of the VMTH during the diagnostic investigation of this dog.

Signalment

Six year old castrated male, mixed breed dog.

History

Two-month history of progressive muscle atrophy of the left side of the head.

Medication

The dog is not presently receiving medication.

Past Medical History

No significant past medical history.

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Physical Examination

 General: Alert and responsive; Body condition score=6. (System range=1-9)

 Rectal temperature: 38.5 (101.4F);

 Heart Rate: 90/m, normal rhythm, femoral artery pulses equal and synchronous.

 Respiratory Rate: 24/m

 Mucosae: pink, capillary refill time: < 2 sec.

 Integument: No abnormalities noted.

 EENT: Lagophthalmos, enophthalmos, OS

 Cardiopulmonary: No abnormalities noted.

 Abdominal cavity: No abnormalities noted.

 Musculoskeletal: No abnormalities noted.

 Lymph nodes: No abnormalities noted.

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Neurological Examination Results

 Consciousness: Alert, responsive.

 Posture: Normal

 Falling: Absent

 Righting reactions: Normal

 Head Tilt: None

 Tremor: None

 Gait: Normal.

 Circling: None observed

 Paresis: Not apparent.

 Postural and Placing Reactions: Normal

 Spinal (segmental) reflexes: (N=normal; D= depressed; A= Absent; I= increased)

 Tendon Reflexes:
Forelimb: N: Extensor Carpi: N: Biceps brachii: N; Triceps brachii: N
Pelvic limbs: Quadriceps: N; Gastroc/Dig. flexors: N.

 Flexion Reflexes: Forelimbs: N; Pelvic limbs: N.

 Crossed Extensor Reflexes: Forelimbs: Not present clinically; Pelvic limbs: Not present clinically.

 Perineal Reflexes: N

 Cutaneous Trunci Reflexes: Present in all normal segmental levels.

 Painful Stimulation: Normal withdrawal responses.

Cranial Nerves

 I: Not tested

 II: Vision apparently normal.

 III, IV, VI: Pupils equal, normal direct and indirect pupillary light reflexes. Normal ocular positions and physiological nystagmus

 V: Left side: Decreased response to sensory stimulation; severe atrophy of temporalis and masseter muscles; Right side: Normal sensory responses; normal musculature.

 VII: Left side: Lagophthalmos; paresis, absence of corneal and palpebral reflexes. Right side: N. (See figure opposite)

 VIII: Righting reactions: N; Physiological Nystagmus: N; Spontaneous nystagmus: absent; Positional nystagmus: absent.

 IX, X, XI: Normal swallowing action in response to stimulation.

 XII: Tongue: position, symmetry, normal movements.

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Tests Performed

Hematology, Chemistry and Urinalysis

Clinical Chemistry Panel Results

Hemogram Results

Imaging Tests - Thoracic Radiographs

Click on the image to see a larger view

	Lateral view of thorax.
	Ventrodorsal view of thorax.

Magnetic Resonance Imaging (MRI) Results

Click on the image to see a larger view

Pathology

Gross Pathology*

* This dog had progressive signs involving both motor and sensory trigeminal function. Imaging revealed a contrast-enhancing mass within the calvaria with distortion of the brain stem. The mass also extended out one or more foramina to involve peripheral part(s) of the trigeminal nerve. The owners declined treatment and requested euthanasia. Necropsy was performed by the University of California Davis Veterinary Medical Teaching Hospital Pathology Service.

Gross necropsy findings of significance

Respiratory system: Multiple pulmonary masses including a 3.0 x3.5 x 1.0 cm firm, raised, mottled white, yellow, red, gelatinous mass in right caudal lung lobe and a 1.1 x 1.0 cm mottled yellow-white mass in the left caudal lung lobe. When sectioned, the latter mass was found to contain a small amount of yellow, creamy material.

Musculoskeletal system: marked atrophy of left temporal and masseter muscles.

Nervous system: There was a 3.5 x 2.0 x 1.0 cm firm tubular, shaped mottled tan-red mass on the extradural surface of the left, ventral brainstem. The mass appeared to be connected to the fifth, sixth and/or seventh cranial nerve(s). It extended through the trigeminal nerve canal in the petrous ridge, involved the nerve tissue rostral thereto, and extended out along the nerves where they emerged through their respective foramina. The adjacent brainstem and the trigeminal nerve roots were slightly compressed.(see figure below).There were no other significant gross lesions except for the muscle atrophy which had been noted clinically and multiple pulmonary masses, one of which yielded a small amount of yellow creamy material when incised.

Click on the image to see a larger view

Histopathology

A and B are specimens from the intracranial part and C and D are specimens from the extracranial part of the mass found at necropsy Click on any image to see a larger view

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Summary

This dog had progressive motor and sensory trigeminal nerve dysfunction. Imaging had revealed a contrast-enhancing mass within the calvaria with distortion of the brain stem. The mass extended out one or more foramina to involve peripheral part(s) of the trigeminal nerve. The owners declined treatment and requested euthanasia. Necropsy was performed by the University of California Veterinary Medical Teaching Hospital Pathology Service.

The gross characteristics of the mass are described separately. Histologically,* the mass consisted of a densely cellular monomorphic population of neoplastic spindle shaped cells extending to the margins examined. The cells were arranged in streaming intersecting patterns. The cells had variably sized elongate, spindle shaped nuclei which tapered at either end. Heterochromatin was evenly distributed without obvious nucleoli. Cells were embedded in an eosinophilic matrix without any defined cytoplasmic borders. There were up to 2 mitotic figures per high powered field [400X mag]. Occasional lymphocytes and plasma cells were infiltrated within the neoplastic tissue. There were large intervening areas of necrosis. (See histopathology sections of this case.)

Thus, grossly and microscopically, the mass conformed closely with descriptions of malignant nerve sheath tumors of the cranial nerves of dogs as in Summers, et al.¹ Although frequently referred to as "malignant schwannomas" it is often difficult to identify the cell of origin of these tumors. In dogs, the incidence of these tumors is higher in spinal nerves than in cranial nerves. Among the latter, the trigeminal nerve is affected most often. Pulmonary metastases, as in this case, are unusual, but provide additional evidence of the malignancy of the tumor.

* VNN is grateful to Prof. Robert J. Higgins for examining the microscopic sections and providing the description above.

Reference

1.  Summers BA, Cummings JF and de Lahunta A, Veterinary Neuropathology (p. 473). Mosby, St Louis Baltimore Berlin Boston Carlsbad Chicago London Madrid Naples New York Philadelphia Sydney Tokyo Toronto 1995. ISBN 0-8016-6328-8

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