Investigation of Draining Sinuses & Tracts
Written by Dr. Penny Tisdall BSc(Vet), BVSc, MVetClinStuds, FACVSc
Draining sinuses are a specific type of non-healing wound. They are tubular ulcers usually lined with granulation tissue to distinguish them from fistula which are tracts connecting epithelial surfaces and may be lined with epithelium. Common causes include foreign material such as grass seeds, sticks, infected surgical implants, bone sequestra or a nidus of infection. Sinuses can occur in many locations but the cervical/ pharyngeal region is commonly affected. Draining tracts can develop fairly distant to the actual location of the underlying cause as inflammatory exudates can track along tissue planes to more ventral locations and may cross the midline. As surgical exploration of the cervical region is complicated by the presence of the oesophagus, larynx and other important neurovascular structures, surgical access is therefore challenging or limited. Identifying the underlying disease process and location prior to surgery may help to facilitate investigation and treatment.
While simple probing of sinuses for superficial material, minor surgical excision (if feasible) or exploration are reasonable initial treatment options, in many cases, the underlying cause is not readily identifiable. Particularly in the cervical region, if sinuses are persistent or recurrent, then imaging may be warranted to try and determine the nature and likely location of an underlying cause. This may be done with ultrasound or radiographs, as they are more readily available. Ultrasound can be useful for localisation of foreign bodies including grass seeds, however, radiographs are frequently not helpful unless there is radiopaque foreign material or bony reactive changes. Radiographic sinography may greatly enhance the usefulness of radiography if there is a sufficiently mature draining sinus tract. This is performed by injection of sterile iohexol into the sinus via a foley catheter during the radiographic exposure. Advanced cross sectional imaging with either contrast enhanced CT scans or MRI should always be considered in challenging regions like the head and neck. While the costs of advanced imaging are initially greater, imaging greatly facilitates surgical investigation with reduced trauma as it allows determination of the presence or extent of underlying disease, anatomic relationships and assists surgical planning. It improves the chances of successful surgical management of these challenging cases.
Treatment of sinuses involves identification and management of the underlying cause. For example, in the case of a 6 month-old Rottweiler puppy, there was persistent neck pain for 4 weeks with later development of a ventral cervical swelling. Surgical exploration was unsuccessful and while a drain was positioned, swelling and discharge continued; there was ongoing wound drainage and sinus formation. Contrast CT scan and sinography was performed and identified a 50 by 4 mm linear filling defect in the retropharyngeal muscles ventral to the cervical vertebra (Fig 1 and B). There was also communication of contrast with the pharynx despite no visible pharyngeal wounds on oral examination. Three dimensional reconstruction (Fig 2) suggested a stick was likely present. Limited ventral cervical approach was performed and the foreign body was recovered and identified as a kebab stick. In this situation, it was not necessary to excise the tract which healed following lavaged. This approach is known as nidus removal.
Other possible approaches to assist in location of foreign bodies include: woundoscopy, using a flexible or semi rigid 1.9 mm scope as well as injection of vital dyes such as methylene blue into the sinus, which can facilitate sinus identification and can be performed immediately prior to or up to 24 hours before surgery. Please note that care must be taken with methylene blue as in cats, it may cause methaemaglobinameia and rarely in dogs, Heinz body anaemia or renal failure. Clinical pathology testing is always indicated, particularly if sinus wounds are explored but an underlying cause is not identified. This could include impression smears, cultures of deep wound discharge and tissue for aerobic and anaerobic bacteria, +/- fungi or other microorganisms and tissue pathology. Culture of discharge from wound surfaces should be avoided as it is only representative of surface contamination.