CASE REPORT MALIGNANT SCHWANNOMA OF THE BRACHIAL PLEXUS IN A DOG BOYDR. JONES, B.V.Sc., and 0. J. WILLIAMS,B.V.Sc. University of Melbourne, Veterinary Clinical Centre, Werribee, Victoria, 3030 Introduction
Schwannomas (neurilemmonas) arise from nerve sheath cells. This neoplasm which may be benign or malignant is most common in cattle but has been observed in the horse,, cat, dog, sheep, goat, pig and mule (Moulton 1961). Moulton (1961) stated that in the dog the usual location for Schwannoma is the skin, especially of the limbs and back. However Schwannomas have been located in cranial nerves (Joshua and Otway 1947), in the brachial plexus (Strafuss et a1 1973), and in the seventh cervical nerve causing spinal cord compression (Boring and Swaim 1973). This paper describes the clinical and pathological findings of a Schwannoma of the brachial plexus in a 4-year-old labrador bitch. Histo,ry and Clinkal Findings
The 4-year-old bitch was first presented for veterinary examination with a history of lameness of the left forelimb for 2 months. Symptoms,
Figure 1. Radiograph of the left shoulder showing area of soft tissue minerallsation (arrow).
40
which were mild initially, became progressively worse with obvious atrophy of muscles of the limb although the dog could still support weight on the limb. The dog was admitted to the University of Melbourne, Veterinary Clinical Centre for clinical and radiological examination. Clinical examination revealed no abnormalities except for left forelimb lameness and generalised atrophy of the left forelimb muscles. Withdrawal reflex, triceps tendon reflex, proprioception and conscious sensation to pin prick to the skin of the limb were normal. Radiographs of banes and joints of the left forelimb and cervical spine showed no abnormalities. The dog was discharged from hospital, no treatment being given. Three months later the dog was returned for re-examination. The left forelimb lameness was still present and muscle atrophy was more severe. The owner reported that the dog occasionally cried out with pain when it jumped, landing on its forelegs. On examination a pain response could
Figure 2. Schwannoma of the left brachial plexus.
Ausrrnlian Veterinary Journal, Vol. 51, January, 1975
be elicited on extension of the left shoulder joint and a firm mass approximately 1 cm in diameter could be palpated medial to the left shoulder joint. A violent pain response was elicited on palpation of this mass. In anteroposterior radiographs of the left shoulder, an area of soft tissue mineralisation could be seen on the medial aspect of the head of the left humerus (Figure 1). Exploratory surgery was performed and the left brachial plexus was exposed. The palpated mass was an enlargement of the radial nerve. Other nerves of the brachial plexus were also affected. A tumour was suspected and although the affected nerves could be excised, the owner did not wish amputation of the limb. Euthanasia was therefore performed and the dog was submitted for autopsy. Autopsy Findings
There was an enlargement of the radial nerve, axillary nerve and the trunk of the median and ulna nerves. The musculocutaneous and suprascapular nerves were not affected. The radial
nerve was thickened to a maximum of 1 cm diameter at the level of the shoulder joint. The lesion terminated dorsally just before the spinal foramen and ventrally at its point of entry into the fascia of the triceps brachii muscle (Figure 2 ) . There were no gross lesions of the brain and spinal cord. Histopathlogy
The lesion consisted of highly cellular neoplastic tissue supported by less cellular collagenous stroma. In several areas there was necrosis of the neoplastic tissue in which mineral had been deposited. The tumour was surrounded by a heavy fibrous capsule. The ceIls comprising the neoplastic tissue were spindle to oblong in shape and were arranged in compact interlacing bands, parallel rows and in a palisading arrangement (Figure 3). There was a rapid change from the dense Antoni Type A tissue into the loosely textured Type B tissue. Mitotic figures were relatively common and there were areas of nuclear pleomorphism (Winston-Evans 1966). A lymphatic
Figure 3. Schwannoma. Showing palisade onentation, interlacing bands and whorls. H and E x240.
Figure 4. Schwannoma. Showing invasion of capsular lymphatic (arrow) H and E x 240.
Ausrralian Veterinary Journal. Vol. 51, January, 1975
41
on the capsular surface had been invaded (Figure 4) but no evidence of metastases were found. The neoplasm was a malignant Schwannoma. Discusdon
The slow development of the clinical signs of lameness, segmental muscle atrophy and hyperaesthesia are characteristic of a slowly developing tumour affecting peripheral nerves or spinal cord. There was no evidence of involvement of the spinal cord in this case as clinical signs were limited to the left forelimb; however tumour involvement of the radial nerve extended to the vertebral foramina and with time could have infiltrated the vertebral canal and caused spinal cord compression. Both the dogs described by Strafuss et a1 (1973) and Boring and Swaim (1973) had hind limb paresis or paralysis after forelimb signs. This was due to compression of the cervical spinal cord by the development of the Schwannoma within the spinal cord. Myelography was used in these cases to localise the area of spinal cord compression by the tumour. The regimentation or palisading of nuclei seen in histological examination of this tumour is a characteristic and important distinguishing feature of Schwannomas (Moulton 1961; Jubb and Kennedy 1970). Schwannomas are slow growing and cause clinical signs when the tumour is large enough to compress the involved nerve(s). Hyperaesthesia before muscle atrophy and paresis was an early feature of the cases described by Strafuss et a1 (1973) and Boring and Swaim (1973) however, in this case pain was observed late in the course of development of clinical signs. In this case an interesting feature was mineralisation of the tumour which was visible in radiographs and confirmed on histological examination.
42
Although areas of necrosis, haemorrhage and mucoid degeneration are encountered in some Schwannomas (Moulton 1961) mineralisation of Schwannomas in animals is not reported. In this dog the main tumour mass is palpable; however if mineralisation is present, radiography may be an aid to localising the site of a Schwannoma in more inaccessible regions of the body. Summary
A 4-year-old Labrador bitch was presented for veterinary examination with a history of lameness and muscle atrophy of the left forelimb. On clinical examination a painful mass was detected medial to the left shoulder joint. Radiographs of the shoulder showed mineralisation of this mass. Exploratory surgery revealed a tumour involving the radial nerve, axillary nerve and the trunk of the median and ulnar nerves. Histopathologic diagnosis was a malignant Schwannoma. Acknowledgments
The authors wish to thank Dr G . Walker for referring the case and Dr B. A. Christie for performing the surgical exploration. References Boring, I. G . and Swaim, S. F. (1973)-1. A m . Artim. Hospt. Ass. 9: 342. Joshua, J 0. and Otway, C. W. (1947)-Vet. Rec. 59: 649. Jubb, K. V. F. and Kennedy, P. C. (1970j-"Pathology of Domestic Animals" 2nd. edn. Academic Press, New York. Moulton, J. E. (1961)-''Tumours of Domestic Animals" University oE California Press, Berkley. Strafuss, A. C., Martin, C. E., Blauch, B., Guffy, M. (1973)-J. A m . vet. med. Ass. 163: 245. Winston-Evans, R. (1966)-"Histological Appearance of Tumours" 2nd edn. Williams and Wilkins, Baltimore. (Received for publication 28 M u y 1974)
Aicstruliun Veterinury Journcrl. Vol. 51, January, 1975
Schwannomas (neurilemmonas) arise from nerve sheath cells. This neoplasm which may be benign or malignant is most common in cattle but has been observed in the horse,, cat, dog, sheep, goat, pig and mule (Moulton 1961). Moulton (1961) stated that in the dog the usual location for Schwannoma is the skin, especially of the limbs and back. However Schwannomas have been located in cranial nerves (Joshua and Otway 1947), in the brachial plexus (Strafuss et a1 1973), and in the seventh cervical nerve causing spinal cord compression (Boring and Swaim 1973). This paper describes the clinical and pathological findings of a Schwannoma of the brachial plexus in a 4-year-old labrador bitch. Histo,ry and Clinkal Findings
The 4-year-old bitch was first presented for veterinary examination with a history of lameness of the left forelimb for 2 months. Symptoms,
Figure 1. Radiograph of the left shoulder showing area of soft tissue minerallsation (arrow).
40
which were mild initially, became progressively worse with obvious atrophy of muscles of the limb although the dog could still support weight on the limb. The dog was admitted to the University of Melbourne, Veterinary Clinical Centre for clinical and radiological examination. Clinical examination revealed no abnormalities except for left forelimb lameness and generalised atrophy of the left forelimb muscles. Withdrawal reflex, triceps tendon reflex, proprioception and conscious sensation to pin prick to the skin of the limb were normal. Radiographs of banes and joints of the left forelimb and cervical spine showed no abnormalities. The dog was discharged from hospital, no treatment being given. Three months later the dog was returned for re-examination. The left forelimb lameness was still present and muscle atrophy was more severe. The owner reported that the dog occasionally cried out with pain when it jumped, landing on its forelegs. On examination a pain response could
Figure 2. Schwannoma of the left brachial plexus.
Ausrrnlian Veterinary Journal, Vol. 51, January, 1975
be elicited on extension of the left shoulder joint and a firm mass approximately 1 cm in diameter could be palpated medial to the left shoulder joint. A violent pain response was elicited on palpation of this mass. In anteroposterior radiographs of the left shoulder, an area of soft tissue mineralisation could be seen on the medial aspect of the head of the left humerus (Figure 1). Exploratory surgery was performed and the left brachial plexus was exposed. The palpated mass was an enlargement of the radial nerve. Other nerves of the brachial plexus were also affected. A tumour was suspected and although the affected nerves could be excised, the owner did not wish amputation of the limb. Euthanasia was therefore performed and the dog was submitted for autopsy. Autopsy Findings
There was an enlargement of the radial nerve, axillary nerve and the trunk of the median and ulna nerves. The musculocutaneous and suprascapular nerves were not affected. The radial
nerve was thickened to a maximum of 1 cm diameter at the level of the shoulder joint. The lesion terminated dorsally just before the spinal foramen and ventrally at its point of entry into the fascia of the triceps brachii muscle (Figure 2 ) . There were no gross lesions of the brain and spinal cord. Histopathlogy
The lesion consisted of highly cellular neoplastic tissue supported by less cellular collagenous stroma. In several areas there was necrosis of the neoplastic tissue in which mineral had been deposited. The tumour was surrounded by a heavy fibrous capsule. The ceIls comprising the neoplastic tissue were spindle to oblong in shape and were arranged in compact interlacing bands, parallel rows and in a palisading arrangement (Figure 3). There was a rapid change from the dense Antoni Type A tissue into the loosely textured Type B tissue. Mitotic figures were relatively common and there were areas of nuclear pleomorphism (Winston-Evans 1966). A lymphatic
Figure 3. Schwannoma. Showing palisade onentation, interlacing bands and whorls. H and E x240.
Figure 4. Schwannoma. Showing invasion of capsular lymphatic (arrow) H and E x 240.
Ausrralian Veterinary Journal. Vol. 51, January, 1975
41
on the capsular surface had been invaded (Figure 4) but no evidence of metastases were found. The neoplasm was a malignant Schwannoma. Discusdon
The slow development of the clinical signs of lameness, segmental muscle atrophy and hyperaesthesia are characteristic of a slowly developing tumour affecting peripheral nerves or spinal cord. There was no evidence of involvement of the spinal cord in this case as clinical signs were limited to the left forelimb; however tumour involvement of the radial nerve extended to the vertebral foramina and with time could have infiltrated the vertebral canal and caused spinal cord compression. Both the dogs described by Strafuss et a1 (1973) and Boring and Swaim (1973) had hind limb paresis or paralysis after forelimb signs. This was due to compression of the cervical spinal cord by the development of the Schwannoma within the spinal cord. Myelography was used in these cases to localise the area of spinal cord compression by the tumour. The regimentation or palisading of nuclei seen in histological examination of this tumour is a characteristic and important distinguishing feature of Schwannomas (Moulton 1961; Jubb and Kennedy 1970). Schwannomas are slow growing and cause clinical signs when the tumour is large enough to compress the involved nerve(s). Hyperaesthesia before muscle atrophy and paresis was an early feature of the cases described by Strafuss et a1 (1973) and Boring and Swaim (1973) however, in this case pain was observed late in the course of development of clinical signs. In this case an interesting feature was mineralisation of the tumour which was visible in radiographs and confirmed on histological examination.
42
Although areas of necrosis, haemorrhage and mucoid degeneration are encountered in some Schwannomas (Moulton 1961) mineralisation of Schwannomas in animals is not reported. In this dog the main tumour mass is palpable; however if mineralisation is present, radiography may be an aid to localising the site of a Schwannoma in more inaccessible regions of the body. Summary
A 4-year-old Labrador bitch was presented for veterinary examination with a history of lameness and muscle atrophy of the left forelimb. On clinical examination a painful mass was detected medial to the left shoulder joint. Radiographs of the shoulder showed mineralisation of this mass. Exploratory surgery revealed a tumour involving the radial nerve, axillary nerve and the trunk of the median and ulnar nerves. Histopathologic diagnosis was a malignant Schwannoma. Acknowledgments
The authors wish to thank Dr G . Walker for referring the case and Dr B. A. Christie for performing the surgical exploration. References Boring, I. G . and Swaim, S. F. (1973)-1. A m . Artim. Hospt. Ass. 9: 342. Joshua, J 0. and Otway, C. W. (1947)-Vet. Rec. 59: 649. Jubb, K. V. F. and Kennedy, P. C. (1970j-"Pathology of Domestic Animals" 2nd. edn. Academic Press, New York. Moulton, J. E. (1961)-''Tumours of Domestic Animals" University oE California Press, Berkley. Strafuss, A. C., Martin, C. E., Blauch, B., Guffy, M. (1973)-J. A m . vet. med. Ass. 163: 245. Winston-Evans, R. (1966)-"Histological Appearance of Tumours" 2nd edn. Williams and Wilkins, Baltimore. (Received for publication 28 M u y 1974)
Aicstruliun Veterinury Journcrl. Vol. 51, January, 1975
