Imaging diagnosis of paranasal sinus mucocele in a Yorkshire Terrier dog

Abstract

An 8-year-old, neutered male Yorkshire Terrier dog presented with left ventromedial canthus swelling over a one-month period, refractory to pharmacological therapy. There was no history of trauma. On ultrasonography, the lesion had a cystic character filled with anechoic fluid and hyperechoic sedimenting debris. The computed tomography (CT) and CT-dacryocystography showed a cystic lesion protruding from the lacrimal sac fossa and occupying a defect in the orbital plate and an ethmoidal ectoturbinate surrounded by a bony structure with an intact nasolacrimal system. The dog underwent the surgical resection of the cyst and its fluid content was aspirated. Ethmoid mucocele was diagnosed based on the CT, cytologic examination, bacterial culture and histopathologic findings. This case describes the imaging characteristics of an ethmoid mucocele and highlights the importance of CT and CT-dacryocystography in dogs with ventromedial canthus swelling that had poor response to medical treatment.

Keywords: canine; computed tomography; dacryocystography; ethmoid mucocele.

Figure 1. Representative extraocular photograph (A) and ultrasonography image [linear transducer, 5–12 MHz (B)] of the ventromedial canthus swelling on the left eye (OS)

Ultrasonography image (B) shows a well-defined, superficial, anechoic, spherical, cystic structure (1.5 cm × 1.7 cm) with partial posterior acoustic enhancement. A mild amount of hyperechoic sedimentation debris is visible in the cystic structure. This cystic structure compresses and dislocate the OS laterally

Figure 2. CT images of the head

Unenhanced (A), contrast-enhanced (B) transverse and reconstructed oblique plane (C) CT in a soft tissue window setting (window width 450 HU, window level 40 HU) shows a non-contrast enhanced cystic lesion (18 HU, asterisk) with a ring enhancement in the caudal part of the left maxillary bone in front of the infraorbital margin. This cystic mass communicates with the nasal concha (black arrowheads) via a bone defect in the orbital plate. Transverse plane (D) with a bone window setting (window width 2 000 HU, window level 600 HU) and a 3D-CT (E) show the new bone formation (arrows) surrounding the cystic mass (asterisk) with the bone erosion of the adjacent maxilla (white arrowhead)

Figure 3. CT-dacryocystography with a bone window setting (window width 2 000 HU, window level 600 HU)

At the level of the nasolacrimal duct opening (A) and nasolacrimal canal (B), the patency of the lacrimal drainage is confirmed by detection of the contrast medium in the nasal meatus (arrowhead). The reconstructed dorsal plane (C) shows the intact left nasolacrimal duct and canal (arrows). The cystic lesion located in the left maxilla is not related to the nasolacrimal duct

Figure 4. CT images of the head

Unenhanced (A) and contrast-enhanced transverse (B) CT with a soft tissue window setting (window width 450 HU, window level 40 HU) show a non-contrast enhanced cystic lesion (35 HU, asterisk) with a ring enhancement in the left frontal sinus. The wall of the frontal sinus has a defect (arrowheads). The transverse (C) and reconstructed dorsal plane (D) CT with a bone window setting (window width 2 000 HU, window level 600 HU) show the new bone formation (arrow) surrounding the cystic lesion (asterisk)