The maxillary sinus is a potential space within the craniofacial skeleton, lined with respiratory mucosa, and adjacent to the oral cavity, nasal cavity, pterygopalatine and infratemporal fossae and the orbit. As such a wide array of diseases can affect the maxillary sinus, and because these disease processes are able to expand to a significant size before causing any symptoms or clinical signs, they can often present late, therefore, presenting both diagnostic and management difficulties. The wide assortment of disease processes is demonstrated in Table 1. Each of these conditions will be detailed with particular reference to recent published data.
EVALUATION OF THE MAXILLARY SINUSES
A patient with isolated maxillary sinus disease may present with a number of clinical symptoms or signs. The commonest presenting features are pain, unilateral nasal obstruction, and epistaxis, although patients may also complain of orbital symptoms, altered facial symmetry, or more rarely oral cavity symptoms. A full history and thorough clinical examination including rigid nasendoscopic examination of the nasal cavity are mandatory, and may identify polyps, pus, or a mass in the nose giving a clue as to the origin of the symptoms. Computed tomography (CT) scanning is widely accepted as the investigation of choice in evaluating the paranasal sinuses, and in-office cone-beam CT scanning is gaining some popularity among endontists to assess whether isolated maxillary disease is odontogenic in origin . MRI is also a useful examination, more readily demonstrating intracranial extension or perineural invasion in the case of a malignancy, or distinguishing fluid from soft tissue. It is particularly useful in identifying fungal disease with hyperintensity on T1-weighted images and hypointensity on T2-weighted images [2▪].
MRI has also been shown to be useful in the diagnosis of silent sinus syndrome . Ultrasound assessment of the maxillary sinuses has been used in the evaluation of ICU patients with a suspected maxillary sinusitis, as a bedside test to detect the presence of fluid in the sinus in those patients too unwell to be transported for a CT scan – a useful adjunct to conventional cross-sectional imaging .
INFECTION OF THE MAXILLARY SINUS
The commonest infections involving the maxillary sinuses are bacterial. The commonest microbial organisms isolated are Staphylococcus aureus, Haemophilus influenza, Moraxella catarrhalis, Streptococcus pneumoniae and beta lactamase producing bacteria – and a recent study into the different flora isolated in smokers and nonsmokers found a higher proportion of MRSA and beta lactamase producing bacteria in smokers with acute and chronic maxillary sinusitis . A dental source of infection should always be excluded. Management is with oral antibiotics, and possibly surgery in the case of failure of antimicrobial therapy. If surgery is required, intraoperative irrigation of the maxillary sinus with saline significantly decreases the bacterial load within the sinus .
Fungal disease can also affect the maxillary sinus in the form of a fungal ball, and the commonest pathogens are Aspergillus sp., namely A. fumigatus and A. flavus, although more unusual pathogens such as Acremonium sp. and Hyalohyphomycosis sp. may be involved and have been recently described [7,8]. The management of a fungal ball is meticulous surgical clearance of the fungal material, with no role for systemic antifungals (Fig. 1). Immunocompromised patients may be affected by a more aggressive invasive fungal infection, mucormycosis, caused by the fungi Mucorales sp.. Rhinocerebral mucormycosis is a rapidly spreading and potentially fatal infection, but in isolated maxillary sinus disease can be managed with immediate surgical debridement and intravenous antifungals .
Rhinoscleroma is a worldwide disease caused by Klebsiella rhinoscleromatis, and is more commonly encountered in temperate and tropical climates . Patients initially present with sore throat and nodular infiltration involving the oropharynx. There are three distinctive and overlapping phases: exudative, proliferative, and fibrotic (cicatricial) . Involvement within the nasal cavity and paranasal sinuses is reported in 95–100%, but isolated maxillary sinus disease has been reported . Management is with appropriate antibiotics in the early phases, surgery reserved for the inevitable scarring and fibrosis which occurs in the later stages of the disease.
SILENT SINUS SYNDROME
Silent sinus syndrome, or imploding antrum syndrome, is a rare disease process caused by unilateral collapse of the maxillary sinus and orbital floor associated with negative antral pressure in the absence of sinus symptoms [11▪▪] and chronic hypoventilation . It typically presents with enophthalmos and hypoglobus, and is characterized by a downward bowing of the orbital floor and a reduction in size of the maxillary sinus [11▪▪]. Diagnosis is made by initial clinical suspicion, and then with CT or MRI  (Fig. 2). Management of this condition is surgical, with endoscopic sinus surgery to re-establish maxillary sinus ventilation, with trimming of a lateralized middle turbinate if found, careful uncinectomy and middle meatal antrostomy. Bony remodelling usually occurs spontaneously over the next few months to restore the orbit to its original position. If this fails to occur, orbital floor repair is considered – although some controversy exists in the literature as to the timing of this aspect of the surgery, some centres advocating repair at the same time as the initial surgery .
The converse problem of pneumosinus dilatans, in which one or more sinuses are dilated without functional alteration, affects the frontal sinus most commonly, followed by the sphenoid, maxillary, and ethmoidal sinuses. The cause is poorly understood, although theories include minor trauma and over aeration of the sinuses . Management is surgical decompression and maxilloplasty .
BENIGN LESIONS OF THE MAXILLARY SINUS
Numerous benign lesions can affect the maxillary sinus, we have outlined here those most frequently encountered.
Mucosal cysts are a common incidental finding on imaging studies, with an incidence between 12.4 and 35.6% . They are typically spherical opacities on CT scanning (Fig. 3), and are not associated with symptoms of chronic rhinosinusitis. No surgical intervention is required, and patients can be simply reassured.
An antrochoanal polyp is a soft tissue mass originating from the maxillary antrum, emerging from the ostium and extending to the choanae through the nasal cavity . These polyps differ from common nasal polyps, as they are solitary, dumbbell shaped, contain fewer mucous glands and eosinophils, and by definition protrude through the choana [16▪]. Presentation is with unilateral nasal obstruction, and diagnosis is made with clinical observation of a large smooth polyp filling the nasal cavity, and possibly extending into the nasopharynx on inspection of the oral cavity, and by characteristic findings on a CT scan (Fig. 4). Bilateral antrochoanal polyps have been reported in the literature rarely [16▪]. The site of origin is most commonly posterior wall, followed by inferior and lateral walls , and management is with endoscopic sinus surgery to remove the polyp in its entirety ensuring removal at the origin via a wide middle meatal antrostomy .
Cholesterol granulomas are benign lesions consisting of granulation tissue, cholesterol crystals, and foreign body giant cells  and are well described in the temporal bone but rare in the paranasal sinuses . These lesions have been described in isolation in the maxillary sinus, and treatment is surgical excision, ensuring complete excision via a large middle meatal antrostomy to minimize the risk of recurrence.
Maxillary sinus mucocoeles are uncommon, the frontoethmoidal region being far more commonly affected. Signs and symptoms reflect the size of the lesion, and in the maxillary sinus can present with diplopia due to elevation of the orbital floor , or with facial swelling or dental problems . Bilateral maxillary mucocoeles have rarely been reported in association with cystic fibrosis . Management is endoscopic sinus surgery, with wide middle meatal antrostomy, allowing adequately wide drainage to prevent recurrence (Fig. 5).
A haematoma or organized haematoma of the maxillary sinus is an uncommon cause of unilateral nasal obstruction and epistaxis, patients also occasionally present with facial swelling or orbital symptoms. Pseudonyms include haemorrhagic pseudotumour, and the problem may present in patients with existing comorbidity such as a bleeding dyscrasia or chronic renal failure . Imaging shows a nonenhancing soft tissue mass on both CT and MRI scanning, with or without bony erosion . Management is endoscopic surgical excision via a wide middle meatal antrostomy, possibly combined with a partial medial maxillectomy, and recurrence is unlikely (Fig. 6).
Pseudotumours of the head and neck classically present in the orbit, but have been described in the maxillary sinus. The histological findings are varied, ranging from predominantly lymphoid tissue to highly fibrotic tissue . A similar lesion is eosinophilic angiocentric fibrosis, lesions caused by eosinophilic perivascular inflammation and gradual replacement with fibrosis . Treatment is surgical excision, although systemic steroid therapy has been used with some success in patients with inflammatory pseuotumours .
Benign tumours of the maxillary sinus
The maxillary sinus can be affected by a number of benign tumours, namely papillomas, fibro-osseous lesions, salivary gland tumours, mesenchymal tumours and vasiform tumours. The most important and commonly encountered of these are discussed below.
Sinonasal papillomas can be classified into inverted, cyclindrical, and everted, the commonest being inverted papillomas. Inverted papilloma occurs in approximately 0.5–4% of all nasal tumours and it is 25 times less frequent than ordinary nasal polyps. Inverted papillomas are benign epithelial tumours, which typically arise from the lateral nasal wall or within the maxillary or ethmoid sinuses, with a characteristic inverted appearance of the epithelium into the underlying stroma, but an intact basement membrane . They can, however, present involving the maxillary sinus in isolation. Although a benign tumour, its potential local aggressiveness, high recurrence rate, and malignant association mandate aggressive treatment [24▪,25].
Patients typically present with unilateral nasal symptoms, and the clinical findings of a polypoid mass in the nasal cavity. Diagnosis is confirmed with CT (Fig. 7) and possibly MRI scanning, and a biopsy for histological diagnosis. Management is surgical excision, and in the vast majority this is possible endoscopically. To ensure successful excision, and to minimize the risk of recurrence, all diseased mucosa should be removed, proceeding to a subperiosteal dissection to include removal of all sclerotic bone, with or without a medial maxillectomy [26▪▪]. Those cases traditionally thought inaccessible endoscopically include tumours with attachments to the anterior wall of the maxillary sinus, but newer techniques such as a maxillary medial sinusotomy have been described, allowing the boundaries of what is achievable endoscopically to be further extended . Patients should be followed up for a minimum of 3 years [26▪▪].
Cyclindrical papillomas typically arise on the lateral nasal wall but have been described in isolation in the maxillary sinus . There is a tendency towards recurrence and malignant transformation, so complete surgical excision is advisable. Everted papillomas are true papillomas lined by stratified squamous epithelium, and although there is less malignant potential, complete surgical excision is the management of choice .
Fibro-osseous lesions are a spectrum of disorders including osteomas, ossifying fibromas, fibrous dysplasia, cement-ossifying fibroma, and osteoblastoma.
Osteomas are benign bony tumours which typically present in the frontal sinuses, often as an incidental finding on X-ray or CT. Isolated maxillary sinus osteomas are exceedingly rare, and account for only 5% of the cases . Various theories as to the pathogenesis of osteomas exist, including chronic inflammation, trauma, and sequestered embryonal tissue [31,32]. Diagnosis is made on appropriate imaging, and if the patient is asymptomatic then management is conservative, adopting a watch and wait policy. If the lesion is particularly large or symptomatic then surgical excision should be considered, and this can sometimes be achieved endoscopically, although often an external or combined procedure is necessary to gain the required access.
Ossifying fibroma is a benign tumour comprised of bone, fibrous tissue, calcification, and cementum [26▪▪]. Radiologically, the lesion is sharply circumscribed with an eggshell rim and central radiolucency. This differentiates it from fibrous dysplasia, which has indistinguishable borders (Figs 8 and 9). Lesions continue to expand inexorably with time, so surgical excision is recommended.
Fibrous dysplasia most commonly affects the maxilla and the mandible in the head and neck, and presents as a painless expanding mass or with the typical ground glass appearance on imaging . Lesions tend to increase in size until patients reach their fourth or fifth decade when the disease process burns out. Surgery is reserved for cases when tumour growth is causing cosmetic deformity or compression on surrounding structures. Some authors have showed regression of lesions on using the bisphosphonate pamidronate .
Cemento-ossifying fibromas are thought to originate from the periodontal ligament and are composed of different amounts of cementum, bone, and fibrous tissue . Tumour growth over time may result in facial asymmetry and displacement of dental roots. Surgical excision is recommended, with regular follow-up as recurrence has been reported.
Salivary gland tumours
Pleomorphic adenomas in the nasal cavity are rare, particularly in the maxillary sinus alone. They are benign tumours, which can be managed with complete surgical excision either endoscopically or via a combined approach. Care is needed as both recurrence and malignant transformation have been reported . Oncocytomas are tumours composed of epithelial or myoepithelial cells with abundant granular eosinophilic cytoplasm, extremely rare in the maxillary sinus. Malignant transformation has been described, so excision is recommended .
Fibromas, lipomas, and myxomas are all uncommon benign tumours in the maxillary sinus. All are managed with endoscopic surgical excision, although myxomas are locally aggressive with a high recurrence rate so a wide local excision is recommended .
Haemangiopericytomas are rare tumours in the head and neck, featuring pericytes (extracapillary cells) distributed around normal vascular channels. Histologically they can be difficult to distinguish from sarcomatous lesions, and they have a variable malignant potential . Wide local excision is mandatory, as late recurrences have been reported, with systemic metastases seen in up to 10%. Follow up should be long term .
Haemangiomas are vascular lesions which can affect the entire sino-nasal cavity but are occasionally found in the maxillary sinus in isolation. They can be endoscopically excised, however, preoperative embolization may reduce intraoperative bleeding and assist the surgery.
MALIGNANT TUMOURS OF THE MAXILLARY SINUS
Squamous cell carcinoma (SCC) is the commonest tumour involving the paranasal sinuses, however, SCC of the maxillary sinus alone is rare, comprising less than 3% of all head and neck carcinomas . Patients often present late, and only once the tumour volume has resulted in oral, orbital, or nasal symptoms. Diagnosis is made with a biopsy for histological diagnosis, and CT and MRI scanning are mandatory, followed by discussion in the multidisciplinary meeting. Management is with either surgery or radiotherapy, or a combination of the two modalities depending on the stage of the tumour, the patient's comorbidities, and local protocols. Other tumours include adenocarcinoma, lymphoma, and adenoid cystic carcinoma to name but a few, but a full discussion of these is beyond the scope of this article.
Maxillary sinus disease is common and numerous disorders can affect this anatomical area. As lesions are frequently allowed to grow to a significant size before becoming symptomatic, patients often present late, which can make management options more limited and difficult. Proper evaluation both clinically and with appropriate imaging allows accurate diagnosis, and lesions can often be successfully managed endoscopically.
Conflicts of interest
The authors can confirm that no funding has been received for this article from any source.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 89).
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