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An infected cyst, associated with a supernumerary fourth molar in the ascending ramus of the mandible, presented with parotid swelling, trismus and pain. It was managed as a parotid infection but recurred and a draining pre-auricular sinus developed, which was thought to be a parotid fistula. This was managed by cautery, followed by excision of the fistula, both of which were unsuccessful. Following this, further investigations revealed that the cause of the facial sinus was in fact a cyst associated with a mandibular fourth molar in the posterior ascending ramus. The tooth was extracted, via a pre-auricular extra-oral approach, under general anaesthetic.
Clinical Relevance: This case shows how a dental panoramic radiograph can be extremely helpful at ruling out certain pathology. It also demonstrates how the symptoms of an infection arising from a tooth in the ramus may be misdiagnosed as salivary gland pathology.
Article
A parotid fistula is a communication between the skin and parotid duct or gland through which saliva is discharged.1 The most common cause is trauma, followed by malignancy, operative complication and infection.2
Supernumerary teeth are additional teeth in the normal series, which may occur in any region of the dental arch, although they are more frequent in the maxilla than the mandible.3 The prevalence ranges from 1.5% to 3.5% in the permanent dentition.4
Odontogenic cysts affect the tooth-bearing region of the jaws, with dentigerous cysts being the second most common type of odontogenic cyst. Dentigerous cysts are formed from the dilatation of the dental follicle surrounding the crown of the tooth. They are attached to the neck of the tooth and often prevent the eruption of the tooth and may even displace it for a considerable distance.5 The degree of displacement may be dramatic, with reports of the mandibular third molar in the ramus, condylar or coronoid regions or to the inferior cortex of the mandible.6 Dentigerous cysts around supernumerary teeth account for about 5% of all dentigerous cysts.7
This is a report of an unusual case that was initially thought to be a parotid fistula but turned out to be a draining pre-auricular sinus from an infected cyst associated with a supernumerary fourth molar, in the posterior border of the ascending ramus.
Case report
A 49-year-old woman was referred by her GMP to the OMFS department with a right parotid swelling. She was complaining of a painful swelling in front of her right ear for one month prior to her appointment. She reported that the swelling had since resolved and that there had been no further episodes of pain and swelling.
Her medical history revealed that she had multiple sclerosis, diagnosed in 2007. She had no known allergies and no prior GA experience. Clinical examination revealed nothing abnormal both extra-orally and intra-orally. As the patient had no complaints, she was discharged.
Four months later the right parotid swelling and pain returned. She developed trismus, and attended her GMP who prescribed amoxicillin 500mg TDS for one week. The patient felt nauseous with 500mg amoxicillin, and so the dose was reduced to 250mg, as the patient was reluctant to take any further type of antibiotics. Her GMP then referred her to an ENT department where examination revealed an erythematous painful right parotid swelling, which was firm to palpate. There was trismus but no palpable lymph nodes. Intra-orally nothing abnormal was detected.
Special tests
An ultrasound scan and fine needle aspiration were carried out. One week later she developed a right pre-auricular draining sinus, which was diagnosed as a parotid fistula. A pus swab was taken of the site, for microbiology culture and sensitivity.
Results of the ultrasound scan showed the swelling had the characteristics of a resolving abscess. Also noted was a small cortical defect in the underlying bone. In view of this, she was advised to see her GDP to rule out a dental abscess. The fine needle aspiration cytology confirmed the presence of an acute inflammatory exudate and benign cytological features.
The isolates from the wound showed a scanty growth of Staphylococcus species and a scanty growth of Corynebacterium species, both of which are normal commensals on human skin.
The fistula was initially treated by cauterization using silver nitrate. The fistula returned and was then excised. Both these local methods failed and the fistula returned, along with increased pain and discomfort and worsening trismus.
A CT (computerized tomography) scan of the face was then requested (Figure 1). This showed asymmetry between the right and left side of the face and that there was soft tissue continuous with right masseter muscle and extending to the skin surface. There was also a resulting defect in the subcutaneous fat at this location and the soft tissue was indistinguishable from the right masseter and extended also to the anterior border of the right parotid gland. The CT scan also showed light inhomogeneous enhancement of this soft tissue and no evidence of lymphadenopathy in the neck, and submandibular glands appeared normal.
Figure 1. Axial view CT scan showing radio-opacity of fourth molar in the right ramus of the mandible.
The patient was then referred back to the OMFS department, where a dental panoramic radiograph was taken and this confirmed the position of the ectopic fourth molar and the associated cyst in the ramus of the mandible on the right-hand side (Figure 2).
Figure 2. A DPT showing the fourth molar in the right ascending ramus and the associated radiolucency.
Treatment
The ectopic mandibular right fourth molar was extracted via a pre-auricular extra-oral approach under general anaesthetic. The right parotid/pre-auricular fistula was excised with an elliptical incision. The parotid was identified and a small area of the capsule was excised (Figure 3).
Figure 3. Patient prepped and draped, with pre-auricular elliptical marking of sinus and marking of border of mandible.
A nerve stimulator was used to ensure there was no damage to the facial nerve. With blunt dissection down the fistula tract, access was gained to the lateral side of the mandibular ramus. Here masseter fibres were cut and dissected and the tooth was identified (Figure 4 and 5).
Figure 4. Retraction with Langenbach retractor and Howarths', with visible fourth molar and use of nerve stimulator.Figure 5. The occlusal surface of the fourth molar, through the pre-auricular approach.
The tooth was then surgically removed with bone removal with burs and elevated and extracted. The area was irrigated, bipolar diathermy was used for haemostasis, and the site was closed in layers with deep vicryl and superficial prolene.
Post-op
The patient's sinus resolved and gradually her mouth opening increased with the aid of jaw opening exercises. She had no facial nerve damage but there was some scarring of the region due to the surgery and the long-standing facial sinus. This will be treated at a later date if the patient wishes to improve the aesthetics.
Discussion
Odontogenic cysts often go unnoticed and are only observed after radiographs are taken for other pathology or when acute inflammation develops.8
This case shows how a dental panoramic radiograph can be extremely helpful at ruling out certain pathology. However, not all general dental practitioners will have a panoramic machine and, currently, all radiographs taken must be justified to comply with IRMER regulations.9 A panoramic radiograph causes less radiation exposure than a CT scan and, considering all the symptoms the patient presented with, it may have been a useful initial test, but it will only show hard tissue pathology within the jaws. CT scanning is the modality of choice for patients with a clinical history and findings suggestive of inflammatory disease of salivary glands, either infectious or non-infectious, including acute, painful, diffuse parotid swelling or recurrent, subacute episodes of mildly painful and tender parotid swelling. Magnetic Resonance Imaging (MRI) is also a commonly used modality of choice when a mass is palpated, whether or not it is tender, solitary or multiple, or discrete or diffuse.10
Ultrasound scanning is the initial imaging modality of choice for the assessment of palpable abnormalities of the parotid gland and also of suspected parotid calculi. Ultrasound scanning is able to demonstrate benign and malignant features of focal lesions and can be used to guide fine needle aspiration biopsy or core biopsy to confirm their nature. Ultrasound scanning is able to guide the need for further imaging (CT or MRI) in those lesions with sonographically malignant features or large masses whose extent is difficult to assess with ultrasound, particularly if deep lobe involvement is suspected.11
Reports of fourth molars in the literature are limited. One reported the presence of bilateral fourth molars in the ramus, which were extracted via an intra-oral approach.12 Another case of the concrescence of a third and fourth molar in the mandible has also been reported.13
There are reports of removal of third molars from the ramus of the mandible via an intra-oral approach, an endoscopic intra-oral approach and an extra-oral approach. The most commonly used extra-oral approaches are submandibular and pre-auricular.14 These external approaches have the advantage of good exposure of the surgical site, but may result in complications such as extra-oral scar formation, damage of joint components, facial nerve injury in the case of pre-auricular access, or damage of the marginal mandibular branch of the seventh cranial nerve in the case of submandibular access.15
The intra-oral approach helps to avoid a visible facial scar and injury to the facial nerve.16 There is still a risk of damage to the inferior alveolar nerve, and access may be limited.
The use of the endoscopic approach has considerable advantages, such as good illumination, clear and magnified visualization of the operating field and, as a result, more conservative surgery. However, the technique requires basic endoscopic equipment and the need for special instruction.17
Each approach is dependent upon the individual case and, in the case of endoscopic, equipment availability. In this report, the extra-oral approach was the most suitable as the patient had severe trismus. The access through a pre-auricular approach was made through her existing facial sinus. The patient was happy with the final results and opted for no further surgery for scar revision.
