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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Inflammation of the paranasal sinuses, usually caused by primary or secondary bacterial infection but sometimes caused by mycotic infection.

Pathophysiology!!navigator!!

  • May be primary, following transient, systemic bacterial infection (usually streptococcal)
  • Bacterial sinusitis commonly occurs secondary to infection of 1 of the maxillary molars (dental sinusitis); the tooth most commonly infected is the first molar
  • Bacterial sinusitis occurs less commonly secondary to necrosis caused by an expanding mass within the sinuses, such as a cyst, neoplasm, osteoma, or progressive ethmoidal hematoma
  • Generally accompanied by empyema that, regardless of its cause, may become inspissated. Inspissated exudate is found most commonly in the VCS
  • Mycosis of the sinuses is caused most commonly by Aspergillus fumigatus
  • All compartments communicate with each other, so all may be involved

Systems Affected!!navigator!!

Respiratory

Genetics!!navigator!!

None

Incidence/Prevalence!!navigator!!

  • Worldwide
  • Primary and secondary bacterial sinusitis is common. Mycotic sinusitis is less common

Geographic Distribution!!navigator!!

  • None for bacterial sinusitis
  • Mycotic sinusitis is seen most commonly in cool, humid climates

Signalment!!navigator!!

No age, sex, or breed predilections

Signs!!navigator!!

General Comments

  • The most common clinical sign, regardless of the cause, is purulent or mucopurulent nasal discharge from the affected side
  • Mycotic infection sometimes results in a sanguineous discharge
  • Horses may uncommonly be affected bilaterally
  • Malodorous nasal exudate is characteristically associated with dental sinusitis, an expanding mass, or mycotic sinusitis, whereas odorless exudate is more characteristic of primary bacterial sinusitis; primary bacterial sinusitis may result in malodorous nasal exudate, especially if exudate becomes inspissated

Historical Findings

A common complication of strangles or may accompany signs of dental disease.

Physical Examination Findings

  • Common signs include ipsilateral epiphora, conjunctivitis, and enlarged submandibular lymph nodes
  • Facial distortion and obstructed airflow are sometimes features of horses with an expanding mass within the sinuses
  • Oral examination may reveal evidence of disease of a maxillary molar or a diastema adjacent to a maxillary molar

Causes!!navigator!!

A complication of strangles or dental disease.

Risk Factors!!navigator!!

  • Horses 1–5 years old are most susceptible to Streptococcus equi var. equi infection and, therefore, are most susceptible to primary bacterial sinusitis
  • The incidence of infundibular caries and periodontal disease, both causes of dental infection, increases with age, as does the incidence of neoplasia
  • Horses that are confined to a stable or have recently undergone sinonasal surgery are at most risk of developing sinonasal mycotic infection

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Bilateral nasal discharge may signal that the right and left sinuses are infected, but bilateral nasal discharge is more indicative of diseases caudal to the nasal septum.

CBC/Biochemistry/Urinalysis!!navigator!!

Usually normal.

Imaging!!navigator!!

  • The different radiodensities of teeth and sinuses necessitate acquisition of multiple radiographs taken at different exposures and positions of the tube head to demonstrate detail of the sinuses and dental structures. The cassette should be positioned on the affected side
  • Radiographs usually show increased opacity of the affected sinuses. Horizontal fluid lines within the sinuses are usually visible on a lateral radiograph of the skull
  • The VCS is the usual site of inspissated exudate. Identifying a soft-tissue density dorsal to the maxillary molars on a lateral radiograph and medial to those teeth on a dorsoventral radiograph is evidence of a mass within the VCS
  • To examine the apices of the maxillary teeth, the cassette is positioned on the affected side, and the tube head is placed dorsally, angled 30° ventrally, and centered on the rostral end of the facial crest
  • Disease of a tooth whose apex resides within the sinuses can be recognized radiographically, with confidence, in only half of the cases
  • CT can often provide additional details of the structures involved but may require general anesthesia

Other Diagnostic Procedures!!navigator!!

  • Percussion may identify loss of resonance within the sinuses
  • The oral cavity should be examined for evidence of dental problems
  • Rhinoscopy may reveal exudate discharging from the sinuses at the drainage angle in the middle meatus or distortion of 1 or both conchae caused by an expanding mass within the sinuses
  • Sinoscopy, performed through a trephine hole, may reveal the presence of exudate, a mass, or mycotic plaques. The VCS can be examined through a portal into the conchofrontal or caudal maxillary sinus, after the bulla of the maxillary septum has been perforated

Pathologic Findings!!navigator!!

  • Cytologic examination and culture of exudate obtained by sinocentesis may help to determine whether sinusitis is caused by primary infection or is secondary to other disease. Multiple bacterial colonies can be cultured if infection is caused by dental disease or a mass. Identifying a single bacterial organism, usually a β-hemolytic Streptococcus sp., during cytologic examination or culture indicates that infection is primary, but sometimes a mixed bacterial population is cultured, obscuring the bacterial agent responsible for initiating the primary infection
  • The cause of sinusitis is determined to be mycotic based on histologic observation of fungal hyphae and conidiophores in plaques removed from the sinuses and on culture of a heavy, pure growth of a potentially pathogenic fungus from the plaques

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

The aim of treatment for primary sinusitis is to resolve infection by administering appropriate antimicrobial therapy and by evacuating exudate. The aim of treatment for secondary sinusitis is to resolve the primary cause.

Appropriate Health Care!!navigator!!

  • Lavage of the sinuses and parenteral administration of antimicrobial therapy to resolve non-inspissated empyema caused by primary bacterial infection. The bacterial organism commonly isolated is usually sensitive to penicillin and other β-lactam antibiotics
  • The sinuses are usually lavaged through an ingress portal created in the conchofrontal or caudal maxillary sinus; the rostral maxillary sinus and VCS are most effectively lavaged, however, through a portal created in the rostral maxillary sinus. The nasomaxillary aperture provides egress for lavage solution
  • Inspissated exudate in the VCS should be suspected when primary bacterial sinusitis fails to resolve with lavage and parenterally administered antimicrobial therapy; inspissated exudate must be removed
  • Mycotic sinusitis can usually be resolved by lavaging the affected sinuses with an antifungal agent (e.g. itraconazole, fluconazole, enilconazole, miconazole, ketoconazole, natamycin, or clotrimazole) for 1–2 weeks
  • To resolve sinusitis secondary to another disease (e.g. dental disease or a mass within the sinuses), the cause of the sinusitis must be resolved, often surgically. Resolving sinusitis secondary to dental infection usually necessitates removing the infected tooth

Nursing Care!!navigator!!

NSAIDs to reduce discomfort.

Activity!!navigator!!

Exercise should be restricted for at least several weeks after signs of sinusitis have resolved.

Surgical Considerations!!navigator!!

  • Inspissated exudate is most easily removed from the VCS through a frontonasal flap, which often can be created with the horse standing. The bulla of the maxillary septum must be perforated to expose the VCS
  • A molar can be extracted or repelled through a trephine hole or maxillary flap. A maxillary molar cannot be removed by lateral buccotomy, and endodontic therapy is often ineffective in resolving dental infection
  • Extracting an infected tooth is usually accompanied by few complications and can be accomplished with the horse standing, whereas repelling a tooth is often accompanied by serious complications and is most commonly accomplished with the horse anesthetized

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Primary bacterial empyema—parenteral administration of an antibiotic to which streptococci are susceptible, usually a β-lactam antibiotic (e.g. procaine penicillin 20 000–50 000 IU/kg IM every 12 h) in conjunction with lavage of the sinuses
  • Sinusitis secondary to other disease—administration of an antimicrobial drug, either broad spectrum or based on results of sensitivity testing of cultured bacteria, in conjunction with removing the source of infection
  • Ancillary treatment for mycotic infection includes systemic administration of sodium iodide (20–40 mg/kg IV once daily) for 2–5 days and then oral administration of organic iodide (ethylenediamine dihydroiodide), until clinical signs have resolved

Contraindications!!navigator!!

Sodium iodide and organic iodide should not be administered to pregnant mares.

Precautions!!navigator!!

Side effects of systemic treatment with sodium iodide or organic iodide include excessive lacrimation, generalized alopecia, cough, abortion, and birth of a hypothyroid foal.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Continued resolution of abnormal nasal discharge after antimicrobial therapy has been discontinued indicates infection has resolved
  • Distortion of the nasal passages caused by an expanding mass resolves within several weeks after the mass has been removed
  • Increased opacity of the sinuses may be observed radiographically long after sinusitis has resolved

Prevention/Avoidance!!navigator!!

  • Vaccination of susceptible horses against S. equi on farms where strangles is endemic may decrease the incidence of primary sinusitis
  • Routine dental care may decrease the incidence of dental disease that leads to dental infection and associated dental sinusitis

Possible Complications!!navigator!!

  • Unsuccessful treatment for primary sinusitis can usually be attributed to retention of inspissated exudate within the VCS
  • Unsuccessful treatment for dental sinusitis can usually be attributed to alveolar infection caused by retention of osseous or dental sequestra within the alveolus or, less commonly, from the presence of inspissated exudate within the VCS

Expected Course and Prognosis!!navigator!!

The long-term prognosis for horses affected by primary or dental sinusitis is good, provided that the horse receives proper treatment.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Horses affected by primary sinusitis caused by S. equi infection may have other sites of infection, including the guttural pouch.

Abbreviations!!navigator!!

  • CT = computed tomography
  • NSAID = nonsteroidal anti-inflammatory drug
  • VCS = ventral conchal sinus

Suggested Reading ⬆ ⬇

Tremaine H, Freeman DE. Disorders of the paranasal sinuses. In: McGorum B, Dixon P, Robinson E, Schumacher J, eds. Equine Respiratory Medicine and Surgery. Philadelphia, PA: WB Saunders, 2006:393–407.

Author(s) ⬆

Author: Jim Schumacher

Consulting Editors: Mathilde Leclère and Daniel Jean