Article #4 (1.5 contact hours)Refereed Peer Review

Der.moid Sinuses:

University of Tennessee

Lisa Miller, DVMKaren Tobias, DVM, MS, DACVS

surgically.

8: After surgery. most patie'ntsrecover smoothly and heal

normally.

A dermoid sinus is a congenital defect in which the skin fails to separatecompletely from the ectodermal neural tube during embryonic develop-ment. Also called pilonidal sinus or cyst or dermoid cyst, the condition,

which occurs most often in Rhodesian Ridgebacks1-Io and Ridgeback-crosses,ll isthought to be inherited.3 Dermoid sinuses have been reported in several otherbreeds as well, including the shih tzu,12 boxer,12 Siberian hUSky,13 chow ChOW,14American cocker spaniel,15 Boerboel,16 Yorkshire terrier, I? English springerspaniel, IS Great Pyrenees,19 wire fox terrier,2O and golden retriever.21

Located along the dorsal midline, these tubular blind sacs extend from theskin ventrally into the underlying tissues. In 1966, Mann and Stratton3described four types of dermoid sinuses based on the extent of penetration intothe subcutaneous tissues (Figure 1):

. Type I extends veQtrally as a cylindrical sac attached to the supraspinous

ligament.. Type II consists of a sac-like portion that is more superficial than that of type

I and is attached to the ligament by a fibrous band.

. Type III is made up of a superficial sac with no attachment to the

supraspinous ligament.. Type IV extends to the spinal canal and is attached to the dura mater.

Since Mann and Stratton's report,3 another type of dermoid sinus-type V-has been described as a true cyst consisting of a closed, epithelial-lined sac.1O,14

www.Vetlearn_cnm

Figure 2-A dermoid sinus canbetween the examiner's fingersMs. Anke Terbruggen)

Figure 1- Types of dermoid sinuses. (Illustrated by Jeffrey A.Leath)

LOCATIONIn Ridgebacks, dermoid sinuses are found most fre-

quently in the cervical or craniothoracic regions but canalso occur in the sacrococcygeal area or on the head. Inthis breed, sacrococcygeal dermoid sinuses are morelikely to communicate with the dura than cervicalsinuses.7 Sinuses in Ridgebacks usually do not occurwithin the characteristic "ridge" of fur but rather cranialor caudal to the ridge. In other breeds in which thiscondition has been described, dermoid sinuses are mostoften found in the cr~ial thoracic region but have beenreported in other regions of the body as well. Examplesinclude a dermoid sinus of the head in an Americancocker spaniel,15 an intracranial dermoid sinus in a wirefox terrier,2O and a dermoid sinus passing through thelumbosacral junction in an English springer spanieV8

Figure 3- This dermoid sinus can be clearly visualized.(Courtesy of Ms. Anke Terbruggen)

high euthanasia rate most likely reflects culling of affectedpuppies by breeders because euthanasia usually occurredin puppies younger than 6 months of age. Dermoidsinuses were the second most common cause of deathor euthanasia in the surveyed population. The totalnumber of Ridgebacks euthanized because of dermoidsinuses (3.2% of the surveyed population) was greaterthan the death/euthanasia rate of Ridgebacks succumbingto vehicular trauma or gastric dilatation-volvulus.

PREVALENCEIn 1996, the Health and Genetics Committee of the

Rhodesian Ridgeback Club of the United States(RRCUS) conducted a nationwide health survey of itsmembers regarding diseases diagnosed in the breedbetween January 1, 1984, and July 15, 1996!2 Resultswere obtained from 1,263 dogs owned by 278 RRCUSmembers and Ridgeback fanciers (48% response rate).The overall prevalence of dermoid sinuses in the sur-veyed population was 5.3% (67 dogs). Forty-one of the67 dogs were euthanized because of the condition. This

GROSS AND HISTOLOGIC APPEARANCEAlthough sinuses may appear as indentations within

the skin, enlargement may occur as a result of a foreignbody type of reaction4 or infection causing abscessationand drainage.16 Histologically, the sinus most often containskeratin, sebum, and hair3; if infected, however, it may

www.VetLearn.com

be felt as a tense band of tissueduring palpation. (Courtesy of

contain inflammatory cells and bacteria.5,12,16.21The lining usually consists of a squamousepithelium with adnexal structures intact.16 Der-moid sinuses, which consist of epidermal anddermal structures, may be distinguished histo-logically from meningocele or meningomyocele,which contain neural or meningeal elements.12

PRESENTATION AND DIAGNOSISMost often, breeders or veterinarians detect

dermoid sinuses in Ridgeback puppies duringroutine health screenings. The sinus feels likea tense band of tissue, 1- to 5 mm in diameter,when the skin is allowed to slip through the .

, , fi 7(F' 2) I h ' cal Figure 4-Fistulogram of a dermoid sinus. Portions of the lamina of C-3

exammer s mgers 19ure . n t e cervI b 'all /- \, , are a sent cram Y larrow/.regIon, smuses often extend to the dorsal spinous process of the second cervical vertebra!4

Sinuses are not always easy to detect, and it may benecessary to shave the area if the veterinarian or ownersuspects that a sinus is present (Figure 3). Small openingson the skin surface filled with keratinaceous debris,inspissated sebum, and tufts of hair may be visible.Adult dogs with undiagnosed lesions may present withdraining pyogranulomatous dermatitis if the sinusbecomes infected and ruptures.14,21 In some dogs, singleor multiple nonpainful swellings that exhibit nodrainage are evident along the dorsal midline.6

If the sinus communicates to the subarachnoid spacevia a defect in the lamina, neurologic abnormalitiesranging from abnormal motor function to posteriorparesis and hyperesthesia may be noted.s,12 The presenceand severity of neurologic signs depend on location ofthe lesion and presence or absence of myelitis orencephalitis secondary to sinus infection,

Survey radiographs of the spine may show a defect inthe lamina if a lesion extends into the bone; radio-graphs may be normal if the sinus is limited to the skin.Diagnosis is confirmed, however, by a fistulogram inwhich a radiopaque, water-soluble, sterile contrastmedium is infused via catheter or needle into the sinusopeningls (Figure 4). Fistulogram results are often usedto determine extent of the sinus and delineate the land-marks for surgery. If the sinus is filled with debris, itsextent may not be evident on fistulography; in thesecases, myelography may be helpful to identify commu-nication with central nervous system structures (Figure5), In rare cases, dermoid sinuses may be associatedwith spinal malformations, such as hemivertebrae, ver-tebral body fusions, and spina bifida-like lesions.12,17

Figure 5-Myelogram (A) and fistulogram (B) of a detmoidsinus (arrows). Dorsal discontinuity of the contrast column isevident at the cranial extent of C-2. An osseous defect is alsonoted in the dorsal spinous process of C2, and positive contrastfrom the fistulogram as well as air are evident within the superfi-cial portion of the dermoid sinus above the vertebral defect.

TREATMENTBreeders often request euthanasia of affected Ridge-

back puppies-whether or not the sinus is actually causing

a clinical problem-because dermoid sinus is classifiedas a "serious defect or fault" by the RRCUS Code ofEthics.22 Treatment may not be required if the sinus isnot causing clinical problems and is not connected tothe dura mater. If the sinus becomes infected, is drainingor swollen, or is causing clinical manifestations, however,the lesion should be removed surgically. 18.24.25

Some authors recommend a course of antibiotic therapy

www.VetLearn.com

Figure 6-(A) With the patient in ventral recumbency, thearea is prepared for surgery. (B) The surgeon dissects aroundthe sinus carefully, demonstrating the fibrous band attachingthe sinus to deeper structures. (C) The patient 7 days aftersurgery. (Courtesy of Ms. Anke Terbruggen)

Figure 6C-7 days after surgery

for several days to weeks before surgery to treat localinfections!! Antibiotics should be chosen based on cul-ture and sensitivity of samples obtained aseptically byaspiration of the deeper tissues. The most common iso-lates cultured from these lesions include Staphylococcusintermedius and Enterococcus Spp.!2.!8 First-generationcephalosporins or amoxicillin-clavulanic acid may beadministered until culture results are available. Ifmeningitis is suspected, a cerebrospinal fluid sampleshould be obtained and submitted for cytologic evaluationand culture.

The surgical area should be clipped and asepticallyprepared with the patient in ventral recumbency(Figure 6A). An elliptic incision is made around theexternal opening of the sinus. Then the fibrotic wallis bluntly dissected to its origin (Figure 6B), and theattachments are freed carefully. Penetrating the sinuscould contaminate the surgical field.!8.24 If the sinusextends down to the dura, a dorsal laminectomy orhemilaminectomy may be necessary to complete theresection.!2.!8.24 Following sinus removal, the surgicalsite should be lavaged copiously with sterile saline.During closure, care should be taken to eliminatedead space by carefully reapposing all tissue layers,particularly the nuchal ligament if it has been tran-

www.VetLeam.com

sected during surgery.S,Z4 Additionally, using a closed-suction drain may reduce seroma formation.

Neurologic deficits may worsen temporarily aftersurgery. IS Despite a guarded prognosis, animals with

neurologic signs often improve clinically or eventuallyreturn to normal activity after removal of the dermoidsinus.1z ,ZI,Z4 Postoperative antibiotics are often continued

if the surgeon suspects contamination or if the dura wasinvolved. Postoperative pain may be controlled withNSAIDs or fentanyl patches placed preoperatively!6

Postoperative complications may include dehiscence,seroma, bacterial meningitis, or recurrence of signsresulting from incomplete excision. Most patients, how-ever, recover smoothly and heal normally (Figure 6C).

ACKNOWLEDGMENTSThe authors acknowledge the Rhodesian Ridgeback Club of theUnited States for the use of information from its 1996 healthsurvey. The authors also acknowledge Ms. Anke Terbruggen andDr. Billy Thomas for the photographs used in this article andMr. Jeffrey A. Leath for the graphic illustrations.

16. Penrith ML, van Schouwenburg S: Dermoid sinus in a Boerboelbitch.] S Aft Vet Assoc 65:38-39, 1998.

17. Fatone G, Brunetti A, Lamagna F, Potena A: Dermoid sinus andspinal malformations in a Yorkshire terrier: Diagnosis and fol-low-up.] Small Anim Pract 36: 178-180, 1995.

18. Pratt IN, Knottenbelt CM, Welsh EM: Dermoid sinus at thelumbosacral junction in an English springer spaniel. ] SmallAnim Pract41:24-26, 2000.

19. Camacho AA, Laus JL, Veleri V; et al: Dermoid sinus in a GreatPyrenees dog. BrtlZil] Vet Res Anim Sci 32:170-172, 1995.

20. Howard-Martin M, Bowles MH: Intracranial dermoid cyst in a

dog.]AVMA 192:215-216,1988.

21. Cornegliani L, Jommi E, Vercelli A: Dermoid sinus in a goldenretriever.] SmallAnim Pract42:514-516, 2001.

22. Pethwick BJ, Brown DS: Rho~sian Ridgeback Club o/the UnitedStates, Inc. 1996 National Health Survey. Available ath ttp:/ /www.rrcus. 0 rg/ assets/h tml/ abou t/heal th~enetics/ 96heal th_survey.hrm; accessed December 2002.

23. Ross GR, Howlett CR: Dermoid sinus in the Rhodesian Ridge-back in Australia. Aust Vet Pract4:173, 181, 1974.

24. Surgery of the integumentary sysrem, in Fossum TW (ed):Small Animal Surgery, ed 2. St. Louis, Mosby, 2002, pp194-195.

25. Scott DW (ed): Muller and Kirks Small Animal Dermatology, ed6. Philadelphia, WB Saunders, 2001.

26. Pascoe PJ, Mathews KA: Perioperative pain management. VetClin NorthAm SmallAnim Pract30:917-932, 2000.

~

con-from

Thetactthe.icine. Choose ..,

ing questions;postage-paid,

. --- -~--in Compendium

A type IV dermoid sinus endsa. as a blind sac in the subcutaneous tissue.b. as a fibrous band attached to the nuchal ligament.c. as a blind sac attached to the nuchal ligament.d. at the spinal canal attached to the dura mater.

2. In Rhodesian Ridgebacks, dermoid sinuses are mostfrequently found ina. the cervical region cranial to the dorsal fur ridge.b. the thoracic region within the dorsal fur ridge.c. the sacrococcygeal region.d. or on the cranium.

3. Dermoid sinuses that communicate with the duramater are more likely to occur in thea. characteristic ridge of fur.b. cervical region.

REFERENCES1. Hofmeyer CFB: Dermoid sinus in a Rhodesian Ridgeback dog.

j Small Anim Pract4(Suppl):5-8, 1963.

2. Antin IP: Dermoid sinus in a Rhodesian Ridgeback dog.jAVMA 157:961-962, 1970.

3. Mann GE, Stratton J: Dermoid sinus in the Rhodesian Ridge-back. j SmallAnim Pract7:631-642, 1966.

4. Gammie JS: Dermoid sinus and removal in a Rhodesian Ridge-back dog. Can vetj27:250-251, 1986.

5. Lord LH, Cawley AJ, Gilray J: Mid-dorsal dermoid sinuses inRhodesian Ridgeback dogs-A case report. jAVMA131:515-518,1957.

6. Hathcock JT, Clarnpett EG, Broadstone RV: Dermoid sinus in aRhodesian Ridgeback. vet Med SmallAnim Clin 74:53-56, 1979.

7. Stratton J: Dermoid sinus in the Rhodesian Ridgeback. vet Rec76: 846, 1964. .8. Leyh R, Carithers RW: Dermoid sinus in a Rhodesian Ridge-

back. Iowa State Univ vet 1:36-39,1979.

9. Stern HI', Quinlan J, Jackson C: A skin condition in RhodesianRidgeback dogs. j SAft vet MedAssoc 10:170-174, 1939.

10. Tshamala M, Moens Y: True dermoid cyst in a RhodesianRidgeback. j Small Anim Pract 41 :352-353, 2000.

11. Larnbrechts N: Dermoid sinus in a crossbred Rhodesian Ridge-back dog involving the second cervical vertebra. j S Aft vet Assoc67:155-157,1996.

12. Selcer EA, Helman RG, Selcer RR: Dermoid sinus in a shih tzuand a boxer. jAAHA 20:634-636, 1984.

13. Cornegliani L, Ghibaudo G: A dermoid sinus in a Siberianhusky. vet Dermatoll0:47-49, 1999.

14. Booth MJ: Atypical dermoid sinus in a chow chow dog. 1}drkrS Aft vet ver69:102-104, 1998.

15. Bailey TR, Holmberg DL, Yager JA: Nasal dermoid sinus in anAmerican cocker spaniel. Can vetj 42:213-215,2001.

www.VetLearn.com

,...: of the 'follow-. ~n~wpr~ nn rhp

c. craniothoracic region.d. sacrococcygeal region.

JANUARY 2003QUIZ ANSWERS

4. According to a survey of Rhodesian Ridgeback ownersand breeders, the prevalence of dermoid sinus over a12.5-year period in the breed was approximatelya. 1%.b.3%.c. 5%.d.7%.

AR77CLE#lThermoplasric Materials for Orthoric Oesign-R. P. Johnson,J. E. Steiss, D. C Soljonen1. e 2. d 3. c 4. d 5. b6. a 7. c 8. c 9. b 10. e

5. Histologically, a dermoid sinus is lined witha. squamous epithelium and hair follicles.b. meninges.c. fibrous tissue.d. mast cells.

AR11CLE #2Update on Canine and Feline Heartworm Tests-C. Dam1. c 2. a 3. b 4. b 5. d6. a 7. c 8. d 9. a 10. b

ARTICLE #3Brachycephalic Syndrome in Dogs-D. A. Koch, S. Arnold,M. Hubler, R M. Montavon1. b 2. c 3. c 4. a 5. e6. a 7. b 8. a 9. d 10. e

6. The diagnosis of dermoid sinus is most often made bya. palpation and inspection.b. survey spinal radiography.c. fistulography.d. myelography. AR11CLE #4

Canine Glucagonoma-N. B. Langer; A. E. Jergem, K G. Miles1. d 2. d 3. b 4. c 5. b6. d 7. a 8. c 9. b 10. a

7. One of the most cdmmon bacteria cultured from der-moid sinuses isa. Streptococcus spp.b. Staphylococcus intermedius.c. Micrococcus spp.d. Actinomyces spp.

AR77CLE #5Hydrallantois in Mares-K L. Stich, I'L. Blanchard1. d 2. b 3. c 4. b6. a 7. c 8. d 9. c

5. d10. c

8. Which statement regarding surgical resection of der-moid sinuses is true?a. The sinus should be opened and followed to its

deepest extent to determine whether dura mater isattached.

b. Dorsal laminectomy or hemilaminectomy may berequired for complete removal.

c. Transection 'of the nuchal ligament during sinusresection does not require primary repair.

d. both band c

9. The mode of inheritance of dermoid sinuses isa. simple recessive.b. simple dominant.c. sex linked.d. undetermined.

10. Which statement regarding dermoid sinuses is true?a. Mfected dogs may have multiple sinuses that do

not penetrate the skin.b. Dermoid sinuses may predispose animals to hyper-

esthesia and posterior paresis.c. Dermoid sinuses are the second most common

cause of euthanasia in Rhodesian Ridgebacks.d. all of the above

www.Vetlearn.com