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CT of the head, soft tissue window pre (left) and post (right) contrast

CT of the head, bone window, sagittal and transverse planes

Dorsal reconstruction pre-contrast, transverse plane fistulography

Volume rendering, non-enhanced (left) and fistulography (right)

A cleft is noted on midline dividing the nasal bone dorsally. A focal convex thickening is noted in the subcutaneous tissues adjacent to this cleft. Following IV contrast administration, a thin-rim of contrast enhancement is noted within this soft-tissue thickening. This oblong tube of thin-rimmed contrast-enhancement measures approximately 0.5 cm in diameter. Rostrally at the level of the maxillary incisors, this tract exits through the skin. Caudally, the soft tissue becomes enclosed circumferentially by bone and has a bony lumen that extends to the cribiform plate.

Approximately 1 mL of contrast was then injected into the tract. The contrast extends caudally for approximately 4.7 cm, as it enters the enclosed bone. This contrast medium does not extend to the ethmoturbinates.

Summary

  • Fistulous tract of the dorsal aspect of the nose tunneling through a bony defect in the nasal bone to the level of the ethmoturbinates. This is most suggestive of a nasal dermoid sinus cyst. Another rule-out would be a follicular infundibular cyst
  • The test was negative for extension to the meninges or brain.

Surgical removal of the cyst was successful. Histopathological analysis revealed a cystic structure lined by a keratinizing, stratified, squamous epithelium. The cyst contained large amounts of keratin and hair shafts. There were multiple small follicles surrounding the cyst wall.

These findings were most consistent with a nasal dermoid sinus cyst.

Discussion

Nasal dermoid sinus cysts are a rare but recognized congenital lesion in dogs resulting from incomplete separation of the skin and neural tube during embryonic development. Dogs usually present at a young age with a non-painful draining tract on the dorsal aspect of the nose.

A differential diagnosis in this case would have been a follicular infundibular cyst. These are non-neoplastic cystic structures that contain an epithelial lining, and are commonly found on the head, trunk, or proximal limb in dogs. However, the gross pathological appearance, midline location, and histopathological pattern of multiple small follicles surrounding the cyst wall are most consistent with a nasal dermoid sinus cyst.

References

  1. Anderson DM, White RAS. Nasal dermoid sinus cysts in the dog. Vet Surg 2002; 31: 303–308.
  2. Bailey TR, Holmberg DL, Yager JA. Nasal dermoid sinus in an American cocker spaniel. Can Vet J 2001; 42: 213–215.
  3. Burrow RD. A nasal dermoid sinus in an English bull terrier. J Small Anim Pract 2004; 45:572–574.
  4. Sturgeon C. Nasal dermoid sinus cyst in a shih tzu. Vet Record 2008; 163: 219–220.
  5. van der Peijl GJW, Schaeffer GF. Nasal dermoid cyst extending through the frontal bone with no sinus tract in a Dalmatian. J Small Anim Pract 2011; 52:117–120.