Journal of Feline Medicine and Surgery (2009) 11, 717e719doi:10.1016/j.jfms.2009.02.005

CASE REPORTDermoid cysts presenting as enlarged thyroid glandsin a cat

Katherine Tolbert DVM1*, Holly M Brown DVM

3, Pauline M Rakich DVM, PhD, DACVP4,

Mary Ann G Radlinsky DVM, MS, DACVS2, Cynthia R Ward VMD, PhD, DACVIM

2

1Department of Clinical Sciences,Section of Internal Medicine,College of Veterinary Medicine,North Carolina State University,Raleigh, NC 27606, United States2Department of Small AnimalMedicine and Surgery, College ofVeterinary Medicine, University ofGeorgia, United States3Department of Pathology, Collegeof Veterinary Medicine, Universityof Georgia, United States4Athens Veterinary DiagnosticLaboratory, College of VeterinaryMedicine, University of Georgia,Athens, GA 30602, United States

*Corresponding author. E-mail: mary_to

1098-612X/09/080717+03 $36.00/0

A 5-year-old spayed female cat was evaluated for hyperthyroidism based on anelevated free thyroxine (T4) measurement and bilaterally enlarged symmetricsubcutaneous masses in the area of the thyroid glands. Physical examinationrevealed bilateral subcutaneous masses on either side of the cervical trachea.Blood was obtained for serum biochemical profile and thyroid function analysis.Mild hyperalbuminemia, mild hypercalcemia, and mildly increased alanineaminotransferase activity were identified. Serum concentrations of total and freethyroxine were within the reference interval. Cytologic analysis of fine-needleaspirates from one of the masses was suspicious for neoplasia. Nuclearscintigraphy revealed no abnormalities. Surgically obtained excisional biopsiesof both masses were submitted for histopathology and diagnosed as bilateraldermoid cysts. After excisional biopsy, the patient recovered without incident.The histopathologic diagnosis of completely excised bilateral dermoid cystsindicated that no further medical or surgical intervention was required. This isthe first report of a cat presenting with bilateral dermoid cysts in the area of thethyroid glands. Histopathologic examination was necessary to make a definitivediagnosis. Practitioners should include cysts in their list of differential diagnosesfor ventral neck masses in cats.

Date accepted: 13 February 2009 � 2009 ESFM and AAFP. Published by Elsevier Ltd. All rights reserved.

A5-year old, 5.0 kg (11 lb) spayed female do-mestic shorthaired cat was referred to theVeterinary Teaching Hospital at the Univer-

sity of Georgia for evaluation and radioactive iodinetreatment of hyperthyroidism. The referring veterinar-ian had diagnosed hyperthyroidism 8 weeks prior topresentation on the basis of an elevated serum freethyroxine by equilibrium dialysis (fT4) concentration(56 pmol/l; reference range, 10e50 pmol/l) and com-patible clinical signs of polyuria and polydipsia andslight weight loss. The serum thyroxine (T4) concen-tration was 3.1 mg/dl (reference range 0.8e4.0 mg/dl).

The cat was bright, alert, and responsive on presen-tation. The heart rate, temperature, and respiratoryrate were 160 beats/min, 101.1�F (38.4�C), and32 breaths/min, respectively. The cat was in goodbody condition (body condition score 2.5/5) and two0.5� 1.0 cm subcutaneous masses were palpated oneither side of the cervical trachea. There was no cervi-cal lymphadenopathy. No other abnormalities werenoted on physical examination. Differential diagnoses

lbert@ncsu.edu

� 2009 ESFM a

considered for the masses included thyroid adenoma-tous hyperplasia, cysts (ie, thyroid, parathyroid), neo-plasia (thyroid or parathyroid adenoma/adenocarcinoma/cystadenoma, squamous cell carcinoma,lipoma, lymphoma), abscess, and salivary mucocele.Initial diagnostics included a complete blood count(CBC), serum biochemical profile, urinalysis, and se-rum T4 and fT4 measurements. Additionally, fine-nee-dle aspiration with cytologic analysis of both masseswas performed. The CBC revealed an elevated redblood cell count (12.59� 106/ml; reference range,5e10� 106/ml), which was attributed to hemoconcen-tration secondary to dehydration. Serum biochemicalabnormalities included hyperalbuminemia (4.4 g/dl;reference range, 3e4.3 g/dl), elevated alanine amino-transferase (ALT) activity (135 U/l; reference range,31e104), and hypercalcemia (11.5 mg/dl; referencerange, 9e10.8 mg/dl). The hyperalbuminemia andhypercalcemia were attributed to hemoconcentration,although hypercalcemia of malignancy was also con-sidered. The mildly increased ALT activity was ini-tially attributed to suspected hyperthyroidism.Urinalysis revealed trace proteinuria, an inactive

nd AAFP. Published by Elsevier Ltd. All rights reserved.

Fig 2. Dermoid cyst, cat. The cyst wall contains a folliculo-sebaceous unit oriented perpendicular to the cyst cavityfilled with lamellar keratin. Hematoxylin and eosin 40�.

Fig 1. Dissection of the right dermoid cyst.

718 K Tolbert et al

sediment, and marked concentration (USPG> 1.060)which was supportive of dehydration. Results of theserum T4 and fT4 were within the reference range at2.6 mg/dl (reference range 0.8e4.0 mg/dl) and13 pmol/l (reference range 10e50 pmol/l), respec-tively. An ionized calcium measurement, performedto more specifically evaluate the hypercalcemia, waswithin the reference range at 1.18 mmol/l (referencerange 1.1e1.4 mmol/l), further supporting hemocon-centration rather than hypercalcemia of malignancy.Thoracic radiography was performed to evaluate forpossible metastasis and findings revealed normal pul-monary vasculature and a normal cardiac silhouettewith no evidence of metastasis. Cytologic analysis ofmodified-Wright-stained fine-needle aspirates fromthe left cervical mass revealed a sparsely cellular sam-ple composed of a population of large cells that variedfrom round to polygonal to caudate with eosinophiliccytoplasm containing blue, and less frequently blackor green, granules that ranged from small and discreteto large aggregates. There was moderate anisocytosisand anisokaryosis with frequent single nucleoli pres-ent. The cells present were suspected to be epithelialin origin, and the moderate cellular atypia was sug-gestive of a neoplastic population. Cytologic analysisof modified-Wright-stained fine-needle aspiratesfrom the right cervical mass revealed abundant kera-tin and cellular debris that was compatible with aspi-ration of a keratin-producing cyst or tumor. As onlya minimal amount of tissue was obtained via aspira-tion, a sample was not submitted for biochemicalanalysis. Because of the historically elevated fT4 andclinical signs compatible with feline hyperthyroidism,nuclear scintigraphy was recommended to evaluatefor functional thyroid tissue and to provide for surgi-cal planning prior to exploratory and excisional biop-sies. Approximately 2.9 mCi of sodium pertechnetateTc99m was administered intravenously and a gammacamera was used to obtain images with a low-energycollimator. The zygomatic salivary glands were morephotoavid than the thyroid glands, and no ectopicthyroid tissue was identified. The examination wasread as normal with a thyroid to salivary gland ratioof 0.5e0.75 on the left side and 0.48e0.6 on the rightside. Taken together, these findings suggested thatthe cervical masses were not comprised hyperplasticor functional thyroid tissue. Surgery was performedfollowing radioactive clearance. Two solitary masses(1� 0.5 cm) were identified adjacent to, but indepen-dent of, both the thyroid and parathyroid glandswhich appeared grossly normal. The masses were su-perficial to the sternohyoideus muscles and were at-tached to the deep surface of the skin. Both masseswere excised with blunt dissection (Fig 1), and the at-tachment to the skin was ligated and excised witheach mass. The cat recovered without incident. Histo-pathology revealed that the two masses were similarand consisted of a single large cyst composed ofa wall of well differentiated stratified squamous epi-thelium encircling a large central cavity containing

lamellar keratin and hair fragments. Small hair folli-cles and sebaceous glands, some of which clearly ex-tended into the cyst cavity, surrounded the cyst (Fig2). The surrounding dermis contained loose collagenwith focally dense mixed inflammatory infiltrates,comprised primarily of lymphocytes and macro-phages with fewer mast cells and neutrophils, associ-ated with infrequent keratin fragments.

Although no thyroid tissue was identified on the as-pirates from the right cervical mass and cytologic find-ings from these aspirates were compatible witha keratin-producing cyst or tumor, the results of the cy-tologic analysis of aspirates from the left cervical masswere more confounding. Although the aspirates weresparsely cellular, the atypia detected within the epithe-lial cell population raised the concern for neoplasia. Ex-cisional biopsy with histopathology was recommendedand pursued, resulting in the final diagnosis of bilateraldermoid cysts. It is suspected that the atypical cells

719Dermoid cysts presenting as enlarged thyroid glands

detected on cytology represented reactive epithelialcells with melanin and/or keratohyalin granules aspi-rated from the cells lining or surrounding the cyst.

Dermoid cysts (DC) are benign follicular structures,classified as congenital inclusion cysts, which aresmall solitary duplications of skin and, therefore, de-rived from mesodermal and ectodermal germlayers.1e3 Histologically, DC are lined by stratified ep-ithelium with surrounding mesodermal components,including sebaceous glands, hair follicles, smoothmuscle, and/or fat tissue.3,4 The invagination of thedermoid cyst is completed by a surrounding layer ofcollagen which envelopes the cystic structure, andthe cyst cavity is often filled with keratin debris andhair fragments and may also contain sebaceous secre-tions.3 A dermoid cyst may resemble a follicular cystor dilated pore of Winer clinically and must be differ-entiated by histopathologic exam.5 Follicular cystsarise from the lining of the hair follicle and are furtherclassified by the level of the follicle from which theyarise. A key distinguishing feature of dermoid cystsis the presence of multiple hair follicles which are con-nected to the cyst wall and whose lumen opens intothe cyst; these are notably absent in follicular cysts.5

Dermoid cysts are rare in cats but this congenitalanomaly has been reported in dogs, with the KerryBlue terrier, Shih Tzu, Boxer, and Rhodesian Ridgebackbreeds being over-represented.3,6,7 Dermoid cysts aresuggested to be an inherited, simple recessive trait inRhodesian Ridgeback dogs where they generally de-tected in younger animals and occur as solitary cysticstructures on the dorsal midline and may extend intothe spinal canal.3,7 Dermoid cysts are found most com-monly on the shoulder and lateral neck in cats.3 The or-igin of DC is controversial but they are thought to arisefrom an incomplete separation of the ectoderm fromthe neural tube during embryologic development.2,3,8

A classification scheme has been developed in humanmedicine which divides congenital dermoid cysts intofour groups based on their location and origin of devel-opment.9 Cysts belonging to group 1 arise in the perior-bital region. Group 2 cysts develop over the dorsalsurface of the nose. Group 3 cysts develop on the floorof the mouth, as in the region of first and second bran-chial arch fusion. Group 4 cysts are thought to developduring fusion of the thyroidal, suprasternal, and suboc-cipital regions.9 The cat presented in the current case re-port would be best classified as group 4, which ischaracterized by cysts occurring in the dorsal or ventralneck region. Surgical excision is recommended for histo-pathologic diagnosis and to prevent secondary infectionor complications associated with cyst enlargement.4,9

The initial finding of an elevated fT4 was mostlikely a result of daily fluctuation, non-thyroidal

illness, or a false-positive result as both repeat mea-surements of T4 and fT4 and radionuclide imagingwere within normal limits.6,10e12 Non-thyroidal illnessmay cause an elevation in fT4 through displacement ofthyroxine from serum binding protein.10,11 False-posi-tive fT4 test results are reported to occur in approxi-mately 5e15% of euthyroid cats.11

For the cat in the current case report, the previous el-evation of free thyroxine, the presence of subcutaneousmasses in the ventral neck, and the cytologic evaluationsuggestive of epithelial neoplasia provided some con-fusion which lead to a diagnostic workup for a thyroidalneoplasm. A literature search of dermoid cysts in catsrevealed a paucity of cases, with no reported cases oc-curring in the vicinity of the thyroid gland.6,8 Despitethe rarity of the condition, dermoid cysts should be in-cluded in the list of differential diagnoses for bilateralventral cervical masses.

References1. Som PA, Sacher M, Lanzieri CF, et al. Parenchymal cysts

of the lower neck. Radiology 1985; 157: 399e406.2. Baker KP, Thomsett LR. Canine and feline dermatology.

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3. Gross T, Ihrke P, Walder E, Affolter V. Skin diseases ofthe dog and cat, clinical and histologic diagnosis.Denmark: Blackwell Publishing, 2005.

4. Gorur K, Talas D, Ozcan C. An unusual presentation ofneck dermoid cyst. Eur Arch Otorhinolaryngol 2005; 262:353e5.

5. Gross T, Ihrke P, Walder E. Veterinary dermatopathology.St Louis: Mosby Publishing, 1992.

6. Rochat MC, Campbell GA, Panciera RJ. Dermoid cysts incats: two cases and a review of the literature. J Vet DiagnInvest 1996; 8: 505e7.

7. Davies ES, Fransson BA, Gavin PR. A confusing mag-netic resonance imaging observation complicating sur-gery for a dermoid cyst in a Rhodesian Ridgeback. VetRadiol Ultrasound 2004; 45: 307e9.

8. Chenier S, Quesnel A, Girard C. Intracranial teratomaand dermoid cyst in a kitten. J Vet Diagn Invest 1998;10: 381e4.

9. Pryor SH, Lewis JE, Weaver AL, Orvidas LJ. Pediatricdermoid cysts of the head and neck. OtolaryngologyHead Neck Surg 2005; 132: 938e42.

10. Peterson ME, Melian C, Nichols R. Measurement of se-rum concentrations of free thyroxine, total thyroxine,and total tri-iodothyronine in cats with hyperthyroidismand cats with non-thyroidal disease. J Am Vet Med Assoc2001; 218: 529e36.

11. Shiel RE, Mooney CT. Testing for hyperthyroidism incats. Vet Clin North Am Small Anim Pract 2007; 37:671e91.

12. Feldman EC, Nelson RW, eds. Canine and feline endocri-nology and reproduction. St Louis: Saunders, 2004.

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