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Schwannoma of the External Auditory Canal in a Filly: A Case Report
Journal of Equine Veterinary Science xxx (2013) 1-4
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Case Report
Schwannoma of the External Auditory Canal in a Filly: A Case Report Nasrollah Ahmadi DVM, PhD a , Ahmad Oryan DVM, PhD a, Mohsen Ghane DVM, PhD b, Bita Geramizadeh MD, PhD c a
Department of Pathology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran c Department of Pathology, Transplant Research Center, Shiraz University of Medical Sciences, Shiraz, Iran b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 November 2012 Received in revised form 6 February 2013 Accepted 26 February 2013 Available online xxx
Schwannomas of the external auditory canal (EAC) are exceedingly rare in human beings and domestic animals. Herein we describe the clinicopathological and immunohistochemical features of a benign schwannoma arising in the EAC of a 2.5-year-old filly. Microscopically, the mass showed a spindle cell tumor composed of hypocellular Antoni type B areas as a myxomatous arrangement of mesenchymal cells and hypercellular Antoni type A areas displaying short fascicles of densely packed neoplastic cells in the collagenous stroma. Immunohistochemically, the tumor cells were diffusely positive for S100 protein and vimentin but negative for Ki67. It was concluded that schwannomas should be included in the differential diagnosis of EAC masses, and immunohistochemical markers such as S100 protein can strongly help in differentiating this tumor from other spindle cell tumors. Ó 2013 Elsevier Inc. All rights reserved.
Keywords: Equine schwannoma External auditory canal Horse Histopathology Immunohistochemistry
1. Introduction Schwannoma (synonym: neurilemmoma, neurinoma or Schwann cell tumor) is a peripheral nerve sheath tumor (PNST) that arises from the neural sheath Schwann cells of the peripheral, cranial, or autonomic nerves in different anatomic locations and can be benign or malignant [1]. The main histological feature of schwannoma is alternating patterns of hypercellular Antoni type A and hypocellular Antoni type B areas with nuclear palisading and Verocay bodies. Immunohistochemically, schwannomas usually shows positive diffuse immunolabeling of S100 protein as a Schwann cell marker [2-5]. In human beings, schwannomas of the head and neck comprise 25%-45% of all schwannomas, whereas those of the middle ear, internal and external auditory meatus, and neck are less frequently involved [6]. Most of these tumors originate from cutaneous or muscular branches of the cervical or brachial plexus [7].
Corresponding University, School Shiraz 71345-1731, E-mail address:
author at: Nasrollah Ahmadi, DVM, PhD, Shiraz of Veterinary Medicine, Department of Pathology, Iran. [email protected] (N. Ahmadi).
0737-0806/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2013.02.007
Benign peripheral nerve sheath tumors (BPNSTs) have been reported in domestic animals, and the most frequent are reports in cattle and dogs [8-10]. In domestic animals, the most common sites of PNSTs are the brachial plexus, intercostal nerves, and heart [2,11,12]. Review of the veterinary medical literature failed to find any report of schwannoma in the equine external auditory canal (EAC). To the best of our knowledge, this is the first case of EAC schwannoma reported in domestic animals. However, here we describe the clinicopathological and immunohistochemical features of a benign schwannoma arising in the EAC of a horse. 2. Case Presentation A 2.5-year-old filly weighing approximately 300 kg was presented with a firm, painless, and well-circumscribed mass totally filling the left EAC (Fig. 1). The neoplastic mass was located in the inferior wall of cartilaginous portion without any hearing loss, bone erosion, or middle ear involvement. There was no evidence of facial weakness, head tilt, or deviation and nystagmus. The horse had no pain or discomfort in the ear, and the auricle was normal.
2
N. Ahmadi et al. / Journal of Equine Veterinary Science xxx (2013) 1-4
Fig. 1. A neoplastic mass was located in the external auditory canal in the inferior wall of cartilaginous portion of the left ear of a horse and totally filled the ear canal (arrows).
Physical examination revealed no lymphadenopathy in the head and neck region and no further significant clinical abnormalities in other locations of the body. In addition, vital signs such as pulse rate, respiratory rate, and rectal temperature were normal. The horse was restrained in an individual stock with a nose twitch and sedated with intravenous xylazine (2%, Alfasan; Woerden-Holland), 0.2 mg/kg body weight (BW), and acepromazine (Neurotranq 1%, Alfasan; Woerden-Holland), 0.02 mg/kg BW. Surgical resection was carried out under local auropalpebral anesthesia with lidocaine (2%, Pasteur Institute of Iran) in a standing position, and mass debris was cauterized by using a hot forceps. Preoperatively, the horse was given intramuscular penicillin G procaine plus streptomycin (40,000 IU/kg plus 1.1 mg/kg), and flunixin meglumine (Flunex 5%; Razak Laboratories, Tehran, Iran), 1.1 mg/kg BW. On gross examination, the tumor revealed a wellcircumscribed, alopecic, nonulcerated, firm, smooth and creamy yellow-colored mass measuring 5 3 cm in diameter (Fig. 2). The excised mass was round to oval, without an apparent vascularity. Cut surfaces of the mass were homogenously solid without any necrosis and hemorrhage (Fig. 3). Sections of different parts of the mass were fixed in 10% neutral buffered formalin (pH 6.8), dehydrated with graded ethanol concentrations, embedded in paraffin wax, sectioned, and stained with hematoxylin and eosin (H&E) and Masson’s trichrome for microscopy examination. Immunohistochemically, the 4mm-thick sections were stained for S100 protein (clone S100; DAKO), vimentin (clone Vim 3B4; DAKO), and Ki67 (clone MIB-1; DAKO). As chromogen, 3,3diaminobenzidine tetrahydrochloride (DAB) was used. All immunohistochemical sections were counterstained with Harris hematoxylin. For negative controls, the primary antibody was replaced with nonimmune serum. Positive internal control (blood vessels) and external control (cutaneous Langerhans cells) were used for expression of vimentin and S100 protein, respectively. Microscopically, the mass showed a moderate to severe spindle cell pattern with indistinct cell borders and
Fig. 2. The tumor, revealing a well-circumscribed, alopecic, nonulcerated, firm, smooth and creamy yellow-colored mass extracted from the ear canal of a horse.
inconspicuous nucleoli (Fig. 4). The unencapsulated tumor mass was composed of hypocellular Antoni type B areas as a myxomatous arrangement of mesenchymal cells with small elongated hyperchromatic nuclei and a small amount of pale eosinophilic, poorly defined cytoplasm (Fig. 5). The tumor also revealed areas of hypercellular Antoni type A arrangements displaying short fascicles of densely packed neoplastic cells in the collagenous stroma, without nuclear palisading pattern or Verocay bodies. There were no nerve fibers within the tumor tissue. No evidence of necrosis, atypia, or mitosis was present. Masson’s trichrome staining revealed small to moderate amounts of intervening collagen fibers forming an irregular, loose stroma. Immunohistochemical study of the tumor cells was positive for vimentin and S100 protein marker (Fig. 6) but negative for Ki67. Based on the histopathological and immunohistochemical features, a benign schwannoma of the EAC was diagnosed. Until now, there has been no recurrence of original tumor during 2 years’ follow-up.
Fig. 3. Cross-section of the tumor of the ear canal of a horse, showing homogenous solid architecture. No necrotic changes or hemorrhages are evident in the section.
N. Ahmadi et al. / Journal of Equine Veterinary Science xxx (2013) 1-4
3
Fig. 4. Benign schwannoma from the ear canal of a horse, showing moderate to severe spindle cell tumor with indistinct cell borders and inconspicuous nucleoli (H&E, 200).
Fig. 6. Benign schwannoma in ear canal of a horse showing diffuse immunoreactivity for S100 protein as a Schwann cell marker (ABC method; hematoxylin counterstain, 400).
3. Discussion and Conclusion
human medicine, schwannoma is the most common neurogenic tumor of the auricular region of the heart, and the most common nerve of origin is the vestibulocochlear nerve [16,17]. The present tumor possibly arose from the cutaneous nerves or neural structures in the EAC. However, the exact origin of such tumors and their causative agents are unknown. There is no published report of schwannoma in the EAC of domestic and wild animals, and this tumor can be considered uncommon in animals. The prevalence of PNSTs appears very low in horses [5] but have been described in the mediastinum [18], heart [19], periorbital region [20], extradurally in the cranium [12], small intestine [21], cutaneous, upper eyelid, and spinal cord [5] and in the perianal region [22]. These PNST cases have been reported in horses with a wide age range of 1 month to 24 years old [5]. Schwannomas may occur in adult horses aged 3 to 16 years old with no breed or sex predisposition [23]. Schoniger et al [14] described 22 equine cutaneous schwannoma in 8 to 25-year-old horses, with a mean age of 16 years old. Of these, 12 (54.5%) solitary cutaneous mass were found on the head and neck. The authors reported one tumor on the ear, but the precise anatomic location of the tumor was not determined. So, to the best of our knowledge, the present case is the first description of benign schwannoma in the EAC of domestic animals. Schwannomas should be differentiated from other spindle cell tumors such as neurofibroma, equine sarcoid, fibroma, fibrosarcoma, myxosarcoma, leiomyoma, leiomyosarcoma, desmoplastic melanoma, and hemangiopericytoma [2,9,20,24-26]. Neurofibromas contain nerve fibers or numerous axons, while similar to our case, these structures are absent or are rare in schwannoma. In addition, neurofibromas lack the Antoni type A and type B patterns [27-29]. Fibrosarcomas and myxosarcomas are positive for vimentin but cannot express S100 protein [3,9]. Leiomyomas and leiomyosarcomas are negative for S100 protein, while desmoplastic melanomas are positive for S100 protein but lack the Antoni type A and type B patterns [15]. On the other hand, melanophages will often be present, and neither Verocay bodies nor
Histopathologic examination of a neoplastic mass showed the typical appearance of a benign schwannoma in the EAC of a horse. Histologically, schwannomas are characterized by different morphological patterns including highly cellular Antoni type A areas composed of densely compact spindle-shaped neoplastic cells arranged in short bundles or fascicles and Antoni type B areas that are less cellular, made of oval to round, loosely arranged cells in which myxoid tissues are often detected [13,14]. In the highly differentiated Antoni type A areas, there may be nuclear palisading and Verocay bodies formed by two compact rows of well-aligned nuclei and cell processes [15]. The equine EAC benign schwannoma presented here had histopathological features similar to those of previous reports of schwannoma of the other locations in human beings and domestic animals. Schwannomas of the external ear and tympanic membranes are exceedingly rare in humans. However, in
Fig. 5. Benign schwannoma from the ear canal of a horse, composed of hypocellular Antoni type B areas in a myxomatous arrangement of mesenchymal cells with small, elongated hyperchromatic nuclei (B) and hypercellular Antoni type A areas displaying short fascicles of densely packed neoplastic cells in the collagenous stroma (A) (H&E, 400).
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N. Ahmadi et al. / Journal of Equine Veterinary Science xxx (2013) 1-4
hyalinization have been reported as a salient feature of intradermal melanocytic tumors with spindle cell morphology and limited pigmentation [30]. The diagnostic histopathologic feature of hemangiopericytoma is perivascular whorls of fusiform cells [31]. Although, this feature may be present in PNSTs, it is usually dominant in hemangiopericytomas. On the other hand, in PNSTs, the neoplastic spindle cells arrange in concentric layers with sclerotic collagen fibers or axons within the center rather than capillaries [10]. In the present case, the concentric whorl pattern with a vascular structure in the center was not found in the neoplastic mass. Immunohistochemically, S100 protein labels most (if not all) neoplastic cells in benign schwannomas [29], and its positivity is accepted as an essential feature of Schwann cell origin of the neoplasm [2,4,5]. Most PNSTs express S100 protein; therefore, its absence tends to eliminate PNST from the differential diagnosis [24]. In our case, diffuse immunopositivity for S100 protein in the neoplastic cells confirmed a Schwann cell origin. To differentiate benign from malignant PNSTs, the histologic criteria such as mitotic index, growth pattern, cellularity, cellular pleomorphism, and necrotic foci can be useful [22]. However, no mitosis, vascular invasion, or metastases together with lack of cellular pleomorphism and negative immunostaining for Ki67 as a proliferative activity marker in the present case confirmed the benign histological appearance of the neoplastic mass. In a previous study, Bogaert et al [24] reported 10 equine sarcoids that so resembled schwannomas, the tumors were originally misdiagnosed on routine histopathology. All 10 were positive for bovine papillomavirus 1 or 2 by PCR and sequencing, and all 10 were immunohistochemically negative for S100 protein and strongly positive for vimentin. The authors strongly recommended PCR for bovine papillomavirus and S100 immunohistochemistry as ancillary diagnostic tools for all equine skin tumors with typical histological features of schwannoma as the most equine PNST. Although, there are no specific immunohistochemical markers for schwannoma, our case revealed that S100 protein and vimentin are expressed in the schwannoma of equine EAC. In conclusion, the present case report showed that BPNSTs and especially schwannomas should be included in the differential diagnosis of EAC masses. Presence of the main classical morphologic features of schwannoma such as Antoni type A and type B patterns along with the immunohistochemical markers such as S100 protein can strongly help to differentiate this tumor from the other spindle cell tumors. However, it is necessary to consider this rare entity as a space occupying lesion in the clinical inspection of the equine EAC and conductive hearing impairment and ear fullness can arise, if the canal obstruction occurs. Acknowledgments The authors are grateful to Mr. G. Yousefi from the Department of Pathology of the Veterinary School, Shiraz University and Dr. Soleimanpoor from the Daneshbod Pathology Laboratory, Shiraz, Iran, for their technical assistance.
References [1] Martins MD, Anunciato de Jesus L, Fernandes KP, Bussadori SK, Taghloubi SA, Martins MA. Intra-oral schwannoma: case report and literature review. Indian Dent Res 2009;20:121-5. [2] Cordy DR. Tumors of the nervous system and eye. In: Moulton JE, editor. Tumors of domestic animals. 3rd ed. West Sussex, UK: University of California Press; 1990. p. 640-63. [3] Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Mesenchymal neoplasms and other tumors. In: Gross TL, Ihrke PJ, Walder EJ, Affolter VK, editors. Skin disease in the dog and cat: clinical and histopathologic diagnosis. 2nd ed. Oxford, UK: Blackwell Science; 2005. p. 722-96. [4] Johnson RC, Anderson WI, Luther PB, Ryan AM. Multicentric Schwannoma in a mature Holstein cow. Vet Rec 1988;123:649-50. [5] Stoica G, Tasca SI, Kim HT. Point mutation of neu oncogene in animal peripheral nerve sheath tumors. Vet Pathol 2001;38:679-88. [6] Berlucchi M, Piazza C, Blannzuoli L, Bagttaglia G, Nicolai P. Schwannoma of nasal septum: case report with review of the literature. Eur Arch Otorhinolaryngol 2000;257:402-5. [7] Colreavy MP, Lacy PD, Hughes J, Bouchier-Hayes D, Brennan P, O’Dwyer AJ, et al. Head and neck schwannomas da 10 year review. J Laryngol Otol 2000;114:119-24. [8] Ahmadi N, Oryan A, Ghane M, Daneshbod Y. Cutaneous schwannoma in a cow. Braz J Vet Pathol 2012;5:81-5. [9] Chijiwa K, Uchida K, Tateyama S. Immunohistochemical evaluation of canine peripheral nerve sheath tumors and other soft tissue sarcomas. Vet Pathol 2004;41:307-18. [10] Pumarola M, Anor S, Borraz D, Ferrer I. Malignant epithelioid schwannoma affecting the trigeminal nerve of a dog. Vet Pathol 1996;33:434-6. [11] Perez J, Martın de las Mulas J, Arenas A, Luque I, Carrasco L. Malignant schwannoma in a red deer (Cervus elaphus). Vet Rec 1998;143:585-7. [12] Williamson LH, Farrell RL. Intracranial schwannoma in a horse. Cornell Vet 1990;80:135-41. [13] Kuwamura M, Yamate J, Kotani T, Takeuchi T, Sakuma S. Canine peripheral nerve sheath tumor with eosinophilic cytoplasmic globules. Vet Pathol 1998;35:223-6. [14] Schoniger S, Valentine BA, Fernandez CJ, Summers BA. Cutaneous schwannomas in 22 horses. Vet Pathol 2011;48:433-42. [15] Gross M, Maly A, Eliashar R, Attal P. Schwannoma of the external auditory canal. Auris Nasus Larynx 2005;32:77-9. [16] Fodor RI, Pastore PN, Frable MA. Neurilemmoma of the auricle: a case report. Laryngoscope 1977;87:1760-4. [17] Yang CH, Su CY, Wei YC, Hwang CF. Schwannoma of the tympanic membrane. J Laryngol Otol 2006;120:247-9. [18] Andreasen CB, Hedstrom OR, Allison P. Mediastinal schwannoma in a horse-cytological, histological and immunohistochemical evaluation. Vet Clin Pathol 1993;22:54-7. [19] Quinn GC, Fews D, Scase TJ, Pearson GR. Malignant peripheral nerve sheath tumor of the heart in a horse. Vet Rec 2005;157:847-9. [20] Lavach JD, Severin GA. Neoplasia of the equine eye, adnexa, and orbit: a review of 68 cases. J Am Vet Med Assoc 1977;170:202-3. [21] Kirchhof N, Scheidemann W, Baumagartner W. Multiple PNS tumors in the small intestine of a horse. Vet Pathol 1996;33:727-30. [22] Sturgeon BPR, Milne EM, Smith KC. Benign peripheral nerve sheath tumor of the perianal region in a young pony. J Vet Diagn Invest 2008;20:93-6. [23] Fernandez CJ, Valentine BA, Smith C, Summers BA. Equine dermal schwannoma. Vet Pathol 1996;33:607 [Abstract 152]. [24] Bogaert L, Van Heerden M, De Cock HEV, Martens A, Chiers K. Molecular and immunohistochemical distinction of equine sarcoid from schwannoma. Vet Pathol 2011;48:737-41. [25] Koestner A, Higgins RL. Tumors of the nervous system. In: Meuten DJ, editor. Tumors in domestic animals. 4th ed. Ames, IA: Iowa State Press; 2002. p. 697-738. [26] Zachary JF. Nervous system. In: McGavin MD, Zachary JF, editors. Pathologic basis of veterinary disease. 4th ed. St. Louis, MO: Mosby Elsevier; 2007. p. 833-972. [27] Goldschmidt MH, Hendrick MJ. Tumors of the skin and soft tissues. In: Meuten DJ, editor. Tumors in domestic animals. 4th ed. Ames, IA: Iowa State University Press; 2002. p. 84-96. [28] Requena L, Sangüeza OP. Benign neoplasms with neural differentiation. Am J Dermatopathol 1995;17:75-96. [29] Skovronsky DM, Oberholtzer JC. Pathologic classification of peripheral nerve tumors. Neurosurg Clin N Am 2004;15:157-66. [30] Smith SH, Goldschmidt MH, McManus PM. A comparative review of melanocytic neoplasms. Vet Pathol 2002;39:651-78. [31] Maxie MG, Youssef S. Nervous system. In: Maxie MG, editor. Pathology of domestic animals. 5th ed. Philadelphia, PA: Saunders Elsevier; 2007. p. 281-458.
Journal of Equine Veterinary Science journal homepage: www.j-evs.com
Case Report
Schwannoma of the External Auditory Canal in a Filly: A Case Report Nasrollah Ahmadi DVM, PhD a , Ahmad Oryan DVM, PhD a, Mohsen Ghane DVM, PhD b, Bita Geramizadeh MD, PhD c a
Department of Pathology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran c Department of Pathology, Transplant Research Center, Shiraz University of Medical Sciences, Shiraz, Iran b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 November 2012 Received in revised form 6 February 2013 Accepted 26 February 2013 Available online xxx
Schwannomas of the external auditory canal (EAC) are exceedingly rare in human beings and domestic animals. Herein we describe the clinicopathological and immunohistochemical features of a benign schwannoma arising in the EAC of a 2.5-year-old filly. Microscopically, the mass showed a spindle cell tumor composed of hypocellular Antoni type B areas as a myxomatous arrangement of mesenchymal cells and hypercellular Antoni type A areas displaying short fascicles of densely packed neoplastic cells in the collagenous stroma. Immunohistochemically, the tumor cells were diffusely positive for S100 protein and vimentin but negative for Ki67. It was concluded that schwannomas should be included in the differential diagnosis of EAC masses, and immunohistochemical markers such as S100 protein can strongly help in differentiating this tumor from other spindle cell tumors. Ó 2013 Elsevier Inc. All rights reserved.
Keywords: Equine schwannoma External auditory canal Horse Histopathology Immunohistochemistry
1. Introduction Schwannoma (synonym: neurilemmoma, neurinoma or Schwann cell tumor) is a peripheral nerve sheath tumor (PNST) that arises from the neural sheath Schwann cells of the peripheral, cranial, or autonomic nerves in different anatomic locations and can be benign or malignant [1]. The main histological feature of schwannoma is alternating patterns of hypercellular Antoni type A and hypocellular Antoni type B areas with nuclear palisading and Verocay bodies. Immunohistochemically, schwannomas usually shows positive diffuse immunolabeling of S100 protein as a Schwann cell marker [2-5]. In human beings, schwannomas of the head and neck comprise 25%-45% of all schwannomas, whereas those of the middle ear, internal and external auditory meatus, and neck are less frequently involved [6]. Most of these tumors originate from cutaneous or muscular branches of the cervical or brachial plexus [7].
Corresponding University, School Shiraz 71345-1731, E-mail address:
author at: Nasrollah Ahmadi, DVM, PhD, Shiraz of Veterinary Medicine, Department of Pathology, Iran. [email protected] (N. Ahmadi).
0737-0806/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2013.02.007
Benign peripheral nerve sheath tumors (BPNSTs) have been reported in domestic animals, and the most frequent are reports in cattle and dogs [8-10]. In domestic animals, the most common sites of PNSTs are the brachial plexus, intercostal nerves, and heart [2,11,12]. Review of the veterinary medical literature failed to find any report of schwannoma in the equine external auditory canal (EAC). To the best of our knowledge, this is the first case of EAC schwannoma reported in domestic animals. However, here we describe the clinicopathological and immunohistochemical features of a benign schwannoma arising in the EAC of a horse. 2. Case Presentation A 2.5-year-old filly weighing approximately 300 kg was presented with a firm, painless, and well-circumscribed mass totally filling the left EAC (Fig. 1). The neoplastic mass was located in the inferior wall of cartilaginous portion without any hearing loss, bone erosion, or middle ear involvement. There was no evidence of facial weakness, head tilt, or deviation and nystagmus. The horse had no pain or discomfort in the ear, and the auricle was normal.
2
N. Ahmadi et al. / Journal of Equine Veterinary Science xxx (2013) 1-4
Fig. 1. A neoplastic mass was located in the external auditory canal in the inferior wall of cartilaginous portion of the left ear of a horse and totally filled the ear canal (arrows).
Physical examination revealed no lymphadenopathy in the head and neck region and no further significant clinical abnormalities in other locations of the body. In addition, vital signs such as pulse rate, respiratory rate, and rectal temperature were normal. The horse was restrained in an individual stock with a nose twitch and sedated with intravenous xylazine (2%, Alfasan; Woerden-Holland), 0.2 mg/kg body weight (BW), and acepromazine (Neurotranq 1%, Alfasan; Woerden-Holland), 0.02 mg/kg BW. Surgical resection was carried out under local auropalpebral anesthesia with lidocaine (2%, Pasteur Institute of Iran) in a standing position, and mass debris was cauterized by using a hot forceps. Preoperatively, the horse was given intramuscular penicillin G procaine plus streptomycin (40,000 IU/kg plus 1.1 mg/kg), and flunixin meglumine (Flunex 5%; Razak Laboratories, Tehran, Iran), 1.1 mg/kg BW. On gross examination, the tumor revealed a wellcircumscribed, alopecic, nonulcerated, firm, smooth and creamy yellow-colored mass measuring 5 3 cm in diameter (Fig. 2). The excised mass was round to oval, without an apparent vascularity. Cut surfaces of the mass were homogenously solid without any necrosis and hemorrhage (Fig. 3). Sections of different parts of the mass were fixed in 10% neutral buffered formalin (pH 6.8), dehydrated with graded ethanol concentrations, embedded in paraffin wax, sectioned, and stained with hematoxylin and eosin (H&E) and Masson’s trichrome for microscopy examination. Immunohistochemically, the 4mm-thick sections were stained for S100 protein (clone S100; DAKO), vimentin (clone Vim 3B4; DAKO), and Ki67 (clone MIB-1; DAKO). As chromogen, 3,3diaminobenzidine tetrahydrochloride (DAB) was used. All immunohistochemical sections were counterstained with Harris hematoxylin. For negative controls, the primary antibody was replaced with nonimmune serum. Positive internal control (blood vessels) and external control (cutaneous Langerhans cells) were used for expression of vimentin and S100 protein, respectively. Microscopically, the mass showed a moderate to severe spindle cell pattern with indistinct cell borders and
Fig. 2. The tumor, revealing a well-circumscribed, alopecic, nonulcerated, firm, smooth and creamy yellow-colored mass extracted from the ear canal of a horse.
inconspicuous nucleoli (Fig. 4). The unencapsulated tumor mass was composed of hypocellular Antoni type B areas as a myxomatous arrangement of mesenchymal cells with small elongated hyperchromatic nuclei and a small amount of pale eosinophilic, poorly defined cytoplasm (Fig. 5). The tumor also revealed areas of hypercellular Antoni type A arrangements displaying short fascicles of densely packed neoplastic cells in the collagenous stroma, without nuclear palisading pattern or Verocay bodies. There were no nerve fibers within the tumor tissue. No evidence of necrosis, atypia, or mitosis was present. Masson’s trichrome staining revealed small to moderate amounts of intervening collagen fibers forming an irregular, loose stroma. Immunohistochemical study of the tumor cells was positive for vimentin and S100 protein marker (Fig. 6) but negative for Ki67. Based on the histopathological and immunohistochemical features, a benign schwannoma of the EAC was diagnosed. Until now, there has been no recurrence of original tumor during 2 years’ follow-up.
Fig. 3. Cross-section of the tumor of the ear canal of a horse, showing homogenous solid architecture. No necrotic changes or hemorrhages are evident in the section.
N. Ahmadi et al. / Journal of Equine Veterinary Science xxx (2013) 1-4
3
Fig. 4. Benign schwannoma from the ear canal of a horse, showing moderate to severe spindle cell tumor with indistinct cell borders and inconspicuous nucleoli (H&E, 200).
Fig. 6. Benign schwannoma in ear canal of a horse showing diffuse immunoreactivity for S100 protein as a Schwann cell marker (ABC method; hematoxylin counterstain, 400).
3. Discussion and Conclusion
human medicine, schwannoma is the most common neurogenic tumor of the auricular region of the heart, and the most common nerve of origin is the vestibulocochlear nerve [16,17]. The present tumor possibly arose from the cutaneous nerves or neural structures in the EAC. However, the exact origin of such tumors and their causative agents are unknown. There is no published report of schwannoma in the EAC of domestic and wild animals, and this tumor can be considered uncommon in animals. The prevalence of PNSTs appears very low in horses [5] but have been described in the mediastinum [18], heart [19], periorbital region [20], extradurally in the cranium [12], small intestine [21], cutaneous, upper eyelid, and spinal cord [5] and in the perianal region [22]. These PNST cases have been reported in horses with a wide age range of 1 month to 24 years old [5]. Schwannomas may occur in adult horses aged 3 to 16 years old with no breed or sex predisposition [23]. Schoniger et al [14] described 22 equine cutaneous schwannoma in 8 to 25-year-old horses, with a mean age of 16 years old. Of these, 12 (54.5%) solitary cutaneous mass were found on the head and neck. The authors reported one tumor on the ear, but the precise anatomic location of the tumor was not determined. So, to the best of our knowledge, the present case is the first description of benign schwannoma in the EAC of domestic animals. Schwannomas should be differentiated from other spindle cell tumors such as neurofibroma, equine sarcoid, fibroma, fibrosarcoma, myxosarcoma, leiomyoma, leiomyosarcoma, desmoplastic melanoma, and hemangiopericytoma [2,9,20,24-26]. Neurofibromas contain nerve fibers or numerous axons, while similar to our case, these structures are absent or are rare in schwannoma. In addition, neurofibromas lack the Antoni type A and type B patterns [27-29]. Fibrosarcomas and myxosarcomas are positive for vimentin but cannot express S100 protein [3,9]. Leiomyomas and leiomyosarcomas are negative for S100 protein, while desmoplastic melanomas are positive for S100 protein but lack the Antoni type A and type B patterns [15]. On the other hand, melanophages will often be present, and neither Verocay bodies nor
Histopathologic examination of a neoplastic mass showed the typical appearance of a benign schwannoma in the EAC of a horse. Histologically, schwannomas are characterized by different morphological patterns including highly cellular Antoni type A areas composed of densely compact spindle-shaped neoplastic cells arranged in short bundles or fascicles and Antoni type B areas that are less cellular, made of oval to round, loosely arranged cells in which myxoid tissues are often detected [13,14]. In the highly differentiated Antoni type A areas, there may be nuclear palisading and Verocay bodies formed by two compact rows of well-aligned nuclei and cell processes [15]. The equine EAC benign schwannoma presented here had histopathological features similar to those of previous reports of schwannoma of the other locations in human beings and domestic animals. Schwannomas of the external ear and tympanic membranes are exceedingly rare in humans. However, in
Fig. 5. Benign schwannoma from the ear canal of a horse, composed of hypocellular Antoni type B areas in a myxomatous arrangement of mesenchymal cells with small, elongated hyperchromatic nuclei (B) and hypercellular Antoni type A areas displaying short fascicles of densely packed neoplastic cells in the collagenous stroma (A) (H&E, 400).
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hyalinization have been reported as a salient feature of intradermal melanocytic tumors with spindle cell morphology and limited pigmentation [30]. The diagnostic histopathologic feature of hemangiopericytoma is perivascular whorls of fusiform cells [31]. Although, this feature may be present in PNSTs, it is usually dominant in hemangiopericytomas. On the other hand, in PNSTs, the neoplastic spindle cells arrange in concentric layers with sclerotic collagen fibers or axons within the center rather than capillaries [10]. In the present case, the concentric whorl pattern with a vascular structure in the center was not found in the neoplastic mass. Immunohistochemically, S100 protein labels most (if not all) neoplastic cells in benign schwannomas [29], and its positivity is accepted as an essential feature of Schwann cell origin of the neoplasm [2,4,5]. Most PNSTs express S100 protein; therefore, its absence tends to eliminate PNST from the differential diagnosis [24]. In our case, diffuse immunopositivity for S100 protein in the neoplastic cells confirmed a Schwann cell origin. To differentiate benign from malignant PNSTs, the histologic criteria such as mitotic index, growth pattern, cellularity, cellular pleomorphism, and necrotic foci can be useful [22]. However, no mitosis, vascular invasion, or metastases together with lack of cellular pleomorphism and negative immunostaining for Ki67 as a proliferative activity marker in the present case confirmed the benign histological appearance of the neoplastic mass. In a previous study, Bogaert et al [24] reported 10 equine sarcoids that so resembled schwannomas, the tumors were originally misdiagnosed on routine histopathology. All 10 were positive for bovine papillomavirus 1 or 2 by PCR and sequencing, and all 10 were immunohistochemically negative for S100 protein and strongly positive for vimentin. The authors strongly recommended PCR for bovine papillomavirus and S100 immunohistochemistry as ancillary diagnostic tools for all equine skin tumors with typical histological features of schwannoma as the most equine PNST. Although, there are no specific immunohistochemical markers for schwannoma, our case revealed that S100 protein and vimentin are expressed in the schwannoma of equine EAC. In conclusion, the present case report showed that BPNSTs and especially schwannomas should be included in the differential diagnosis of EAC masses. Presence of the main classical morphologic features of schwannoma such as Antoni type A and type B patterns along with the immunohistochemical markers such as S100 protein can strongly help to differentiate this tumor from the other spindle cell tumors. However, it is necessary to consider this rare entity as a space occupying lesion in the clinical inspection of the equine EAC and conductive hearing impairment and ear fullness can arise, if the canal obstruction occurs. Acknowledgments The authors are grateful to Mr. G. Yousefi from the Department of Pathology of the Veterinary School, Shiraz University and Dr. Soleimanpoor from the Daneshbod Pathology Laboratory, Shiraz, Iran, for their technical assistance.
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