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Equine vet. J . (1992) 24 (4) 329-331

Branchial cyst in a filly S. R. HANCE, J. T. ROBERTSON and J. R. WICKS The Ohio State University, College of Veterinary Medicine, Department of Veterinary Clinical Sciences, and 'Department of Veterinary Pathobiology, 1935 Coffey Rd., Columbus, Ohio 43210, USA

History A 10-month-old Belgian filly was admitted to The Ohio State University College of Veterinary Medicine Hospital because of a retrophqngeal swelling. The swelling was first noted 2 months before admission and had rapidly increased in size in the previous 2 weeks. The referring veterinarian had aspirated the mass, producing a thick yellow fluid.

Clinical signs On examination, the filly carried her head in an extended position with the mass appearing bilaterally symmetrical. The mass extended from the caudal angle of the mandible to the midcervical region and was f m and non-painful on palpation. A bilateral mucopurulent nasal discharge was present. Auscultation revealed bilateral respiratory crackles in the ventral lung fields. A mild tracheal rattle was present. When stressed, the filly would become dyspnoeic and demonstrated inspiratory stridor. Radiographs of the laryngeal and cranial cervical regions revealed an oval, soft tissue opacity approximately 30 cm in length extending from the cranial margin of the second cervical vertebra to the caudal aspect of the third cervical vertebra (Fig 1). The cranial trachea was displaced ventrally and compressed dorsally, decreasing the diameter by one-half. The guttural pouches were slightly displaced cranially with the laryngeal

structures appearing normal. A fluid/gas intdtface was not observed within the mass. Ultrasonographic examination of the mass revealed an anechoic, fluid-filled structure with a hyperechoic capsule. Several small hyperechoic fimbriae were observed moving freely within the fluid when the mass was simultaneously palpated. These were interpreted as possible fibrin tags or septa. Endoscopic examination demonstrated a caudally displaced larynx with rostra1 displacement of the dorsal pharyngeal arch. The arytenoid cartilages were unable to abduct maximally. but adduction was normal. These findings were assumed to be related to the severe caudal retraction of the larynx and ventral displacement of the trachea by the mass.

Clinical pathology The hair over the left side of the neck was shaved and surgically disinfected for a percutaneous aspirate. An 18-gauge needle was inserted into the mass at the point of greatest distension just dorsal to the maxillary vein. A slightly opaque, amber, viscous fluid was collected. A 10 ml sample was submitted for aerobic and anaerobic culture and cytology. Bacteria were not isolated from the specimen. Cytological evaluation of the fluid revealed a total leucocyte count of 500/pl with the predominant cell type being lymphocytes with an occasional large mononuclear cell or macrophage observed. The total protein was 5.2 g/dl with a specific gravity of 1.031. A haemogram indicated leucocytosis with a mature neutrophilia (WBC 18.9/pl, PMNS 15.1/pl). The plasma The leucocytosis and fibrinogen was 400 ddl. hyperfibrinogenaemia were attributed to the mild respiratory infection.

Treatment

Fig 1 : Lateral radiograph of the cranial cervical region with a 30 cm, ovoid mass, (arrowheads) displacing the cranial trachea ventrally and producing dorsal compression of the lumen. The guttural pouches are minimally displaced cranially with laryngeal structures appearing normal

Antibiotic therapy was initiated for the respiratory infection and consisted of 22.00 iu penicillin G potassium (Pfizerpenm, Roerig, Hizer, New York 10017, USA) /kg bwt, iv, 4 times/day, and 1.8 mg gentamicin sulphate (Gentocina, Schering Co., Kenilworth, New Jersey 07033, USA) /kg iv, 3 times/day. One day after admission the filly was anaesthetized. A tracheotomy was performed distal to the cyst because of difficulty in passing an endotracheal tube. The horse was positioned in dorsal recumbency and a 30-cm incision was made medial to the right linguofacial vein, extending down the proximal one-third of the neck. The fascia between the sternohyoideus and stemocephalicus muscles was incised and the trachea retracted to the left side. The cystic structure was well circumscribed, encapsulated and loosely attached. It was located between the longus colli muscle and the trachea. It was bluntly dissected from the loose connective tissue and removed intact. The cyst measured 28 x 14 x 14 cm with the capsule smooth and free of adhesions (Fig 2). The cyst was not loculated and contained approximately 1 litre of viscid, amber

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Fig 2: Phorograph nf rhe itirucr, thin wulleri bruiicliiul q s r removed frnm the cranial ten-ical region. The cyst coiiruiiied upprnsinmtely I litre nf \ k i d . amber tliiid

fluid. The inner lining was irregular with a moderate number of small fibrin tags interspersed over the surface. A section of the lining and capsule was submitted for histological examination. The rostra1 half of the incision was closed by suturing the sternocephalicus to the sternohyoideus muscle in a simple interrupted pattern with No. 2 polyglactin 910 (Vicryl. Ethicon, Inc., Johnson & Johnson Co., Somerville, New Jersey 088760151. USA). The skin in the same location was closed in simple interrupted pattern with No. 0 polypropylene (Prolene, Ethicon, Inc). The remaining dead space was filled with sterile gauze packing. The antibiotics were discontinued post-operatively. On the 2nd day after surgery the filly was febrile with a temperature of 40.7"C. The respiratory rate was 60 breaths/min and thoracic auscultation revealed crackles and wheezes bilaterally. Antibiotic therapy was again initiated by administering 22.000 iu procaine penicillin G k g bwt, intramuscularly, every 12 h and trimethoprim sulphamethoxazole (Trimethoprim sulfamethoxazole. Mutual Pharmaceutical Co. Inc., Philadelphia. PA I9 124. USA), I5 mgkg bwt, orally, every 12 h. Antibiotic therapy was continued for 8 days until the temperature was normal. The gauze pack was removed 3 days after surgery with the wound being allowed to heal by second intention. Endoscopic examination was performed 3 days after surgery, indicating normal positioning of the larynx, and the arytenoid cartilages had a normal range of movement. The filly was discharged I I days after surgery.

Pathology Samples of the cyst were fixed in a 10% buffered-formalin and were cut into 5 pm sections and stained with haematoxylin and eosin. On histological examination, the mass consisted of a large cystic cavity surrounded by mature fibrous connective tissue, with widespread mucinous degeneration. One third of the cyst was lined by simple cuboidal to squamoid epithelium. Beneath the epithelium was mature fibrous tissue as above or a layer of granulation tissue with mild infiltrates of lymphocytes, plasma cells, histocytes and neutrophils. Occasional foci of necrosis with mineralisation were present in the granulation tissue layer. Areas devoid of epithelium had granulation tissue alone, or granulation tissue projected from the cyst wall into the lumen. The diagnosis, based on microscopic examination, was consistent with a cervical cyst lined by cuboidal to squamoid epithelium. The chronic inflammatory changes were interpreted as probably secondary to repeated trauma. Branchial cysts have been reported in dogs (Karbe and

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Nielsen 1965, 1966; Clark, Kostolich and Mosier 1989), cats (Joffe 1990) and cattle (Smith and Gunson 1977). These cysts arise from abnormal retention of the branchial apparatus. In man 4 pairs of branchial arches develop as ridges around the lateral cervico-facial area during the 4th week of embryogenesis. These arches are separated into 4 paired outer clefts and 4 paired inner pharyngeal pouches with the clefts and pouches being composed of ectodermal and endodermal tissue respectively. The first pharyngeal pouch forms the guttural pouch (eustachian tube), middle ear and mastoid cells with the 2nd pouch giving rise to the supratonsillar fossa. The thymus and upper parathyroid glands are derived from the 3rd pouch, while the 4th pouch gives rise to the lower parathyroid glands and contributes to the formation of the thyroid gland (Noden and de Lahunta 1985; Soper and Pringle 1987). Based on location, cyst contents, lack of attachment to other structures and the presence of an epithelial lining, the cervical cyst in this case is compatible with a branchial cyst, which based on its anatomical location is most likely derived from remnants of the 2nd pharyngeal pouch. Since the branchial apparatus is composed of ectodermal and endodermal tissue, retained remnants may be lined with stratified squamous epithelium, ciliated stratified columnar epithelium. transitional epithelium, or cuboidal epithelium (Rickles and Little 1967). This may explain the presence of both squamoid and cuboidal epithelium lining the cyst in this case. Additionally, depending on the environmental stimuli, metaplasia may occur, changing ciliated stratified columnar, transitional and cuboidal epithelium to squamous epithelium. This metaplastic change explains the prevalence of stratified squamous epithelium in branchial cysts in man (Rickles and Little 1967). There are two reports of a cystic structure in the neck region of horses, one of which was a foal and the other was 2 years old (Mayhew and Lumsden 1973; Field, Trout and Physick-Sheard 1990). Both horses were presented for swelling in the cranial cervical region which was non-painful to palpation. Cytological features, radiographic appearance and clinical presentations were similar to those of the case presented here. However, histological findings were inconclusive in the previously reported cervical cysts, prohibiting conjecture regarding their origin. Both of these cases, however, were conceivably the result of retained branchial remnants. Histologically, one cyst had small areas which resembled cholesterol clefts (Mayhew and Lumsden 1973) and, because cholesterol crystals are characteristically observed in fluid from human branchial cysts, it may be reasonable to consider that the cyst originated trorn branchial remnants (Titchener and Allison 1989). The cyst in the second case was characterized by granulation tissue with multifocal areas of squamous epithelium which may also represent a branchial cyst (Field et a/ 1990). Additionally, 2 horses with a cystic structure within a guttural pouch have been documented. These cysts may have also been associated with the retention of the first branchial cleft (Hance, Robertson and Bukowiecki, 1992). The horse in this report was 8 months of age when clinical signs were first observed. Nevertheless, it remains likely that this was a congenital abnormality. Clinical signs of cystic formation in man are not generally recognised until early adulthood (Bhaskar and Bernier 1959; Rickles and Little 1967; Soper and Pringle 1987). It is maintained that secretory filling of the cysts is delayed and cystic filling is a prerequisite to recognition (Soper and Pringle 1987). Percutaneous aspiration and surgical drainage are considered inappropriate because most cysts reappear if any epithelium remains (Soper and Pringle 1987; Doi, Hutson, Myers and McKelvie 1988). A possible different diagnosis for cervical swelling would include a salivary mucocoele. Salivary mucocoeles, like branchial cysts, are cystic cavities which contain a slightly viscous, clear fluid, but they lack an epithelial lining (Noden and de Lahunta 1985). A cervical abscess could also have similar clinical signs, but abscesses are usually painful and are easily differentiated by

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cytological evaluation and culture. The present case depicts the first known description of a branchial cyst in the horse. The case was unique due to the large size of the cyst and the rapid accumulation of fluid that induced the clinical signs. Diagnosis was made by anatomical location, cytological evaluation of the fluid and histological examination of the epithelial lining. Intact surgical removal was therapeutic.

Assoc. (in press). Joffe. D.J. (1990) Branchial cyst in a cat. Can.vef. J. 31,525-526. Karbe. E. and Nielsen, S.W. (1965) Brachial cysts in a dog. J. Am. vet. med. Assoc.

147.637-640.

Karbe. E. and Nielsen, S.W. (1966) Canine ranulas. salivary mucoceles and branchial cyst. J. Small Anim. Pracf. 7,625-630. Mayhew, I.G. and Lumsden, J.H. (1973) A cervical cyst in a horse. Can. vet. J. 14, 46-49.

Noden, D.M. and de Lahunta. A. (1985) Pharynx and pharyngeal pouches. In: The

References Bhaskar. S.N. and Bernier. J.L. (1959) Histogenesis of branchialcysts; a report of 468 cases. Am. J. Pafh. 35.407424. Clark. D.M.. Kostolich. M. and Mosier, D. (1989) Branchial cyst in a dog. J . Am. vet. med. Assoc. 194.67-68.

Doi. 0..Hutson. J.M., Myers, N.A. and McKelvie, P.A. (1988) Branchial remnants: a review of 58 cases. J . Pedian: Surg. 23.789-792. Field, J.R., Trout. D. and Physick-Sheard. P.W. (1990) Ablation of a congenital neck mass in a foal. Can. vet. J. 31,643-614. Hance. S.R.. Robertson, J.T. and Bukowiecki. C.F. (1992) Cystic structures within the guttural pouch (auditory tube diverticulum) in two horses. J. Am. vef. med.

Embryology of Domestic Animals: Developmental Mechanisms and Malformations. Eds D. M. Noden and A. de Lahunta. Williams & Wilkins, Baltimore. pp 270-278.

Rickles, N.H. and Little, J.W. (1%7) The histogenesis of the branchial cyst II. A study of the lining epithelium. Am. J . Pafh. 50,765-777. Smith, D.F. and Gunson. D.E. (1977) Brachial cyst in a heifer. 1. Am. vef. med. Assoc. 171.64-66.

Soper, R.T. and Pringle, K.C. (1987) Cysts and sinuses of the neck. In: Pediorric Surgery. 4th edn. Eds: K.J. Welch. J.G. Randolph. M.M. Ravitch. J.A. ONeill Jr and M.I.. Rowe. Year Book Medical. Chicago. pp 539-552. Titchener, G.W. and Allison, R.S. (1989) Lateral cervical cysts: a review of 42 cases. N.Z. med. J . 102,536-537.

Receivedfor publication: 16.8.91 Accepted: 30.10.91

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Branchial cyst in a filly.

EQUINE VETERINARY JOURNAL 329 Equine vet. J . (1992) 24 (4) 329-331 Branchial cyst in a filly S. R. HANCE, J. T. ROBERTSON and J. R. WICKS The Ohio...
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