Determining the definitive cause of chronic nasal discharge can be challenging, as there are numerous potential factors that can contribute to it, including nasal and nasopharyngeal disease (13). In dogs, nasal disease can arise as a secondary condition due to anatomical, infectious, inflammatory, neoplastic, and dental factors (10,13). Radiography, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) are valuable diagnostic imaging techniques for investigating the nasal cavity and nasopharyngeal lesions (3). CT is particularly useful for identifying nasal cavity and nasopharyngeal lesions and their respective structures (3,5).

Nasal foreign bodies are often challenging to diagnose, as many of them, particularly grass foreign bodies, may not be distinguishable on CT scans, with over half remaining undetected (11). Therefore, the use of rhinoscopy, including retrograde rhinoscopy for direct visualization of the nasal cavity and nasopharyngeal lesions, is crucial (14). In clinical practice, it is important to consider nasal foreign bodies as a differential diagnosis (5,13), as they can enter either anterogradely by inhalation or retrogradely during swallowing or regurgitation from the nasopharynx (5,9).

This case report describes a patient presenting clinical symptoms of nasal discharge and sneezing, with findings related to choanal stenosis and an undetected grass foreign body on diagnostic imaging examination.

An 8-year-old castrated male Maltese dog was presented for evaluation of chronic bilateral nasal discharge of four months’ duration. The dog had a history of stertorous respiration since a young age and suddenly presented with acute sneezing and unilateral purulent nasal discharge after returning from a trip to the beach. These symptoms led the patient to visit a local animal hospital, where it received antibiotics for two weeks without any improvement. Furthermore, the symptoms worsened, leading to bilateral purulent nasal discharge. As a result, CT and anterograde rhinoscopy were performed at a local animal hospital. A complete blood count (CBC) and serum chemistry profile revealed that, apart from hypercholesterolemia (cholesterol level of 399 mg/dL [reference range: 110-320 mg/dL]), all other parameters were within the normal range. The CT scan showed mild unilateral regional destruction of the left nasal turbinates, along with soft tissue opacification consistent with exudates. Additionally, deviation of the nasal septum is observed (Fig. 1). During the rhinoscopic evaluation, the nasal mucosae were observed to be mildly edematous and erythematous bilaterally. Biopsies of the nasal mucosa revealed a large amalgamation of mucin mixed with scattered moderate numbers of neutrophils and fewer numbers of lymphocytes with small amounts of hemorrhage, indicating subacute to chronic rhinitis. Initial treatment with antibiotics and anti-inflammatory medication led to temporary improvement in clinical symptoms. However, after tapering and discontinuing the medications, the symptoms reappeared and worsened shortly thereafter.

Figure 1. Transverse (A) and parasagittal CT images (B). The CT scan results revealed a deviation of the nasal septum and a hyperattenuating lesion (arrow) in the left nasal cavity.

Therefore, the dog was referred to a veterinary teaching hospital. Physical examination revealed normal vital signs, with occasional sneezing observed during the examination. Bilateral purulent nasal discharge was present. Nasal patency testing showed a patent airway on the right side, but no patency on the left. No nasal pain, asymmetry, or depigmentation of the nares was observed. Complete blood count revealed mild regenerative anemia, with white blood cell (WBC) and neutrophil counts within normal range. The serum chemistry profile showed elevated levels of alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transpeptidase, along with hypercholesterolemia and hypertriglyceridemia. Coagulation tests, including prothrombin time and partial thromboplastin time, were unremarkable.

The dog underwent a CT scan and was premedicated intravenously with butorphanol (Butorphanol tartrate Inj, Myungmoon Pharm Co., Seoul, Korea; 0.2 mg/kg) and midazolam (Midazolam Inj, Bukwang Pharm Co., Seoul, Korea; 0.2 mg/kg). General anesthesia was induced using propofol (FrEEfol-MCT Inj, Daewon Pharmaceutical Co., Seoul, Korea; 4 mg/kg), followed by endotracheal intubation with a cuffed 3 mm endotracheal tube. Anesthesia was maintained with isoflurane in oxygen. A CT scan of the nasal cavity and sinuses revealed bilateral partial choanal atresia, with the posterior choanae symmetrically narrowed and flat in appearance (approximately 5 × 2.5 mm each), containing minimal gas due to the presence of fluid (Fig. 2). Both nasal cavities contained abundant fluid, causing a loss of air contrast in most of the nasal cavity at the level of the frontal bone. A small amount of fluid was also noted in the nasopharynx, but its diameter remained adequate. In addition to the nasal findings, mild bilateral otitis externa was observed, with slight thickening of the ventral portions of the horizontal ear canals, along with contrast enhancement. Fluid was also noted in both tympanic cavities, which had not been observed in previous evaluations. The right tympanic cavity displayed marked contrast enhancement, while the left did not show significant enhancement.

Figure 2. Transverse (A) and parasagittal CT images (B) of the nasal cavity and sinuses demonstrating bilateral choanal partial atresia (arrow) along with abundant fluid within both nasal cavities.

Following the CT scan, a nasal cytobrush procedure and a discharge swab were performed. The samples were processed for cytological examination, bacterial culture, and PCR testing for canine respiratory pathogens. Cytological analysis of the cytobrush sample revealed a substantial presence of degenerative neutrophils, along with clusters of respiratory epithelial cells, suggestive of active inflammation (Fig. 3). Discharge samples were submitted to a commercial laboratory for bacterial culture, antibiotic susceptibility testing, and PCR analysis to identify potential pathogens. The dog was prescribed doxycycline (Doxycline tablet, Young Poong Pharma Co., Incheon, Korea; 5 mg/kg PO q 12 hr), N-acetylcysteine (Acetylcysteine capsule, PharmGen Science, Seoul, Korea; 10 mg/kg PO q 12 hr), bromhexine (Bromhexine Hydrochloride tablet, SINIL PHARMA Co., Seoul, Korea; 2 mg/kg PO q 12 hr), famotidine (Famotidine tablet, NELSON Pharma Co., Seoul, Korea; 0.5 mg/kg PO q 12 hr), silymarin (Legalon cap, Bukwang Pharm. Co.; 10 mg/kg PO q 12 hr), ursodeoxycholic acid (Ursa tab, Daewoong Pharmaceutical Co., Seoul, Korea; 10 mg/kg PO q 12 hr), and prednisolone (Solondo tablet, Yuhan Co., Seoul, Korea; 0.5 mg/kg PO q 12 hr), prescribed due to suspicion of severe edema and inflammation. All medications were administered for 7 days.

Figure 3. Cytobrush results demonstrating numerous degenerative neutrophils along with a cluster of respiratory epithelial cells (arrow). 400× (A), 1,000× (B), H&E stain.

Seven days after the CT scan, the patient returned for a follow-up visit, and rhinoscopy was performed. A notable finding was neutrophilic leukocytosis (neutrophil count: 16.96 K/µL, reference range: 2.95-11.64 K/µL; WBC: 21.41 K/µL, reference range: 5.05-16.76 K/µL). The C-reactive protein level was within the normal range at 0.5 mg/dL (reference range: 0-1 mg/dL). Premedication and anesthesia were administered as before. Rhinoscopy was conducted with the dog in ventral recumbency, and an endotracheal tube (3 mm) with an inflated cuff was maintained throughout the procedure. Retrograde rhinoscopy of the choanae was performed using a flexible endoscope (Karl Storz, Tuttlingen, Germany; 5.9 mm in diameter, 110 cm in length). Upon insertion of the endoscope, a grass foreign body was observed in the choanal area (Fig. 4). It had a flat shape, measuring approximately 0.5 × 4.5 cm. The foreign object was effectively removed by vigorously flushing saline through the nasal passages and utilizing grasping forceps.

Figure 4. Endoscopic photographic views of the nasopharynx with a nasopharyngeal grass foreign body before (A) and after (B) grass foreign body removal. The removed grass foreign body is shown in (C).

PCR testing from a week earlier returned negative results, while bacterial culture identified Pseudomonas aeruginosa. Since Pseudomonas was resistant to doxycycline, treatment was switched to marbofloxacin (MARBOCYL, Vetoquinol, Lure, France; 2 mg/kg q 24 hr for 7 days), to which the bacteria were susceptible. Based on the culture results, the previously prescribed prednisolone (Solondo tablet; 0.5 mg/kg PO q 24 hr for 7 days) was tapered. Following the removal of the foreign body, the original clinical signs, such as nasal discharge and sneezing, resolved without complications. It was confirmed that the left nostril’s patency had returned. During the three-month follow-up period, the patient remained symptom-free.

Grass foreign bodies are often not detected on CT evaluation, which highlights the limitations of CT in detecting organic materials like grass. These foreign bodies are frequently radiolucent or small, making differentiation from surrounding soft tissues difficult. Studies indicate that only a small percentage of grass foreign bodies are confidently identified on CT scans, with detection rates ranging from 5% to 42%, depending on the study (6,8,11). Even with secondary signs like turbinate destruction or mucosal thickening, direct visualization remains challenging. Given these limitations, combining CT imaging with rhinoscopy is essential for a comprehensive assessment. While CT can provide valuable structural information and identify secondary signs, rhinoscopy allows for direct detection and removal of foreign bodies. This case underscores the need for complementary diagnostic approaches, with rhinoscopy being particularly effective when CT findings are inconclusive. Multiple studies confirm that both antegrade and retrograde rhinoscopy significantly enhance the identification and extraction of foreign objects, ensuring a thorough evaluation of the nasal cavity (2). In our case, recognizing that foreign bodies may not always be detectable on CT, exploratory rhinoscopy was performed. A grass foreign body was identified and successfully removed during retrograde rhinoscopy.

Thus, even when imaging shows no abnormalities, direct examination of the nasal cavity via rhinoscopy is necessary. Furthermore, although no distinctive features were found on CT evaluation, the local hospital performed only an antegrade assessment. Retrograde rhinoscopy was limited by the patient’s weight (less than 5 kg) and the larger diameter of the endoscope. However, in this case report, the foreign body was identified through retrograde evaluation. Therefore, both antegrade and retrograde rhinoscopy should be performed to fully assess the nasal structures. Given CT’s limitations, especially in small-breed dogs with chronic nasal symptoms, combining antegrade and retrograde rhinoscopy is essential for a comprehensive evaluation. Anterior rhinoscopy with a rigid endoscope and posterior rhinoscopy with a flexible endoscope provided accurate diagnoses in 55.8% and 26.9% of cases, respectively. However, when both methods were combined, diagnostic accuracy rose to 82.7% (7). Retrograde rhinoscopy allows for thorough examination of the posterior nasal cavity and nasopharynx, areas that are often difficult to visualize with antegrade rhinoscopy or CT. This method is particularly valuable for detecting not only foreign bodies but also structural abnormalities, inflammatory diseases, or tumors. In small dogs with compact nasal structures, retrograde rhinoscopy becomes even more important. In this case, retrograde rhinoscopy was crucial for identifying and removing a foreign body that was missed during initial CT and antegrade rhinoscopy. Moreover, even in the absence of foreign bodies, retrograde rhinoscopy is a vital diagnostic tool for assessing structural or pathological abnormalities in the nasal and nasopharyngeal regions. Thus, in small-breed dogs with persistent nasal symptoms, early use of both antegrade and retrograde rhinoscopy, alongside CT, is recommended for accurate diagnosis and timely treatment. In summary, rhinoscopy is valuable for thoroughly examining the nasal cavity, even when CT reveals no specific findings in patients with nasal discharge and symptoms.

Choanal stenosis is rare in both dogs and cats (1,4). Choanal atresia is thought to result from the failure of the bucconasal membrane to rupture during embryonic development, leading to the absence of communication between the nasopharynx and nasal cavity (11). Stenosis can also develop as a secondary result of upper airway infections, inflammation, trauma, or ulceration (1,4,12). Choanal atresia alone can cause symptoms such as stertorous or stridorous breathing, sneezing, and gagging (1,12). Treatment options include various surgical procedures to resect the abnormal tissue causing the stenosis and balloon dilation of the affected area (4,12). In this patient, the foreign body was likely vomited into the nasopharynx, as its size was significantly larger than the patient’s nasal cavity, and it became lodged in the stenotic area. This created a complex interaction between the anatomical structure and the foreign object. Since symptoms did not recur after the foreign body removal, a repeat CT scan was not performed due to the owner’s financial constraints. For the same financial reasons, tissue analysis was also not performed, preventing differentiation between congenital and secondary causes of stenosis.

Grass can cause nasopharyngeal foreign bodies. However, while grass is one of the most common foreign bodies in the nasal cavity, it is uncommon in the nasopharyngeal region (2,5). Additionally, most studies report foreign bodies in the nasal cavity and nasopharynx in large dogs weighing more than 10 kg (2,5). The significance of this case is that it involved a grass foreign body in the nasopharynx of a dog weighing less than 5 kg.

Through this case report, clinicians should be aware that even if the imaging evaluation appears normal or suggests an anatomical structural abnormality, the possibility of a foreign body should still be considered. This case also indicates the significance of performing retrograde nasopharyngoscopy in such cases.

This work was supported financially by Rural Development Administration (RDA) under grant number RS-2023-00232301 and ”Regional Innovation Strategy (RIS) (No. 1345370809)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2021RIS-002).

The authors have no conflicting interests.