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INTRODUCTION
Acute rhinosinusitis often follows an upper respiratory tract infection. It is estimated that only 0.5 % to 2 % of viral upper respiratory tract infections are complicated by bacterial superinfection, with the prevalence rates for acute rhinosinusitis varying from 6 % to 12 % [1].
Regarding rhinosinusitis complications, epidemiological studies estimate an incidence of three cases per million per year [2].
Acute bacterial frontal sinusitis [FS] is relatively uncommon and, in the case of isolated frontal involvement, is usually unilateral at presentation [1,3].
Typically, patients with acute FS come to medical attention with low-grade fever, malaise and frontal headaches, often accompanied by marked tenderness of the medial aspect of the infraorbital margin [1,4]. The majority of complications tend to occur in children and young adults due to the relative thinness of the sinus walls and increased vascularity of the frontal bone [5].
The infection usually responds to antibiotics with the correct antimicrobial spectrum coverage, which varies geographically, depending on the prevalence of amoxicillin resistance [3].
The most common organisms implicated in FS are Streptococcus pneumoniae, Hemophilus influenzae and anaerobic streptococci [2].
The anatomic location and venous drainage pattern of the frontal sinus can lead to severe and life-threatening complications when the infection spreads to adjacent structures. Complications arising from the frontal sinus usually involve the intracranial compartment, although the infectious process can also progress to the orbit or adjacent bone and soft-tissue structures [4].
With this article, we aim to provide a concise and practical review of the published work on complications of frontal rhinosinusitis that will be useful for the day-to-day use in the clinical practice.
MATERIAL AND METHODS
A review of the literature was performed by the authors (Figure 1).
Figure 1. PRISMA diagram illustrating the search strategy for this review. Adapted from Page et al. [22].
PubMed (www.ncbi.nlm.nih.gov/pubmed/) database was searched with relevant terms, which included the following: «frontal sinusitis complications», «pediatric frontal sinusitis» and «frontal sinusitis imaging». Relevant scientific treaties were also used as ancillary to this review.
A comprehensive review of the English and Portuguese literature was carried out, including papers published between 2000 and 2021. Our inclusion criteria included clinical trials, expert opinion papers, literature reviews, systematic reviews, and clinical guidelines. Duplicate articles, case reports or very small sample studies were excluded prior general screening. One epidemiological retrospective study outside the time scope of this review [21] was added for epidemiological data.
RESULTS
Twenty-one studies met the inclusion criteria (Appendix 1, Table 1). Most of them concerned the adult population, with four papers directly addressing the pediatric population. Two clinical guidelines[1,6], one large retrospective cohort study [2] and two systematic reviews were selected [5,7]. Twelve clinical review articles and small retrospective studies were selected, [8,9,18,10–17] comprising most of the papers addressed. Four clinical textbooks [3,4,19,20] were also consulted for this review.
DISCUSSION
The true incidence of FS is still controversial [1,2]. One study reported 91 treated patients from a population of 250.000 inhabitants over 9 years. The age range was 9 to 65 years, with a male preponderance, with a male to female ratio of 3:1 [21].
These numbers are probably underestimated due to the fact that not all patients with frontal sinusitis seek medical attention [1,2,6].
Numerous predisposing factors for frontal sinusitis have been proposed in the literature, including [1,8]: allergic and vasomotor rhinitis, mucociliary disorders, immunosuppression, previous sinus surgery, chemical exposure, previous surgery or cocaine abuse.
Morbidity and mortality from complicated sinusitis are mainly related to intracranial involvement.
In the setting of high clinical suspicion of intraorbital and intracranial complications, Magnetic Resonance Imaging [MRI] with and without intravenous contrast is most appropriate, due to its excellent soft-tissue resolution. However, its limited availability and need for sedation in pediatric patients may impair its use [13]. From a practical stand point, the fact that most of these complications are approached in emergency setting (where MRI is often not readily available) makes contrast-enhanced Computed Tomography (CT) the most performed first-line imaging modality by far [3].
Although the mortality rate was higher before the era of antibiotic therapy [4], intracranial abscess still carries a mortality rate as high as 40 %, with an additional 40 % of patients suffering permanent physical disabilities [9].
EXTRACRANIAL COMPLICATIONS
Osteomyelitis and Pott Puffy Tumor
Frontal sinusitis can involve adjacent bone either by direct extension or by thrombophlebitis of the diploic veins [4]. The bone marrow of the frontal bone can become involved giving rise to osteomyelitis, which constitutes about 9 % of acute rhinosinusitis complications with the frontal sinus being the most frequently involved sinus [10].
Pott puffy tumor (Figure 2) is a subperiosteal abscess that results from osteomyelitis of the frontal bone, located in the anterior wall and usually seen as a complication of frontal sinusitis or head trauma [3]. It is a rare but serious complication, more common in young adults, although it can be also seen in children. Presenting symptoms of osteomyelitis and Pott’s puffy tumor include swelling of the forehead, headache, photophobia, and fever [11].
Figure 2. Potts puffy tumor: Sagittal [left] and axial [right] enhanced-CT, soft-tissue [left] and brain [right], shows frontal sinus opacification associated with frontal tumefaction corresponding to a subperiosteal abscess. Erosion of the frontal bone anterior wall can be seen, in keeping with osteomyelitis.
CT is usually the first imaging modality in the emergency setting. It confirms the presence of ARS, with opacification, mucosal thickening and air-fluid levels in the sinuses, and is the modality of choice to depict cortical bone erosions and/or trabecular demineralization, the main signs of osteomyelitis [13].
Due to the high risk of associated intracranial complications, early diagnosis and adequate surgical and antibiotic treatment are mandatory [10,11]. If the patient is clinically stable, medical treatment and simple external drainage of the abscess could be preferred, using a drill hole or even puncture needle to prevent scarring of the acute inflamed frontal recess [10]. According to the literature regarding long bones osteomyelitis, intravenous antibiotic therapy should be maintained for a minimum of 6 weeks [4].
Orbital Complications
Frontal sinusitis alone rarely causes an orbital complication [3]. These are usually due to ethmoidal sinusitis, followed by maxillary, frontal, and, more rarely, sphenoidal sinusitis [1].
Orbital complications occur in 6 % of cases of acute rhinosinusitis [ARS], more commonly in the pediatric population [12,13].
CT is usually diagnostic and shows thickening and densification of the eyelid, with no changes in the postseptal area, namely extraocular muscles, postseptal fat and lacrimal glands [13].
Cases of preseptal and orbital cellulitis are usually treatable with medical therapy alone, namely intravenous antibiotherapy and corticosteroid. On the other hand, more severe complications usually require surgical drainage [including the affected sinuses] coupled with intravenous antibiotherapy, although medical treatment alone may be successful and initially attempted in selected cases of subperiosteal abscess [14].
With early treatment, orbital complications have a good prognosis, although some symptoms, such as proptosis or orbitary edema, could take up two to three months to fully recede [19].
Cavernous Sinus Thrombosis
It may be considered an orbital or intracranial complication, resulting from retrograde thrombophlebitis of the ophthalmic vein or direct extension of sphenoidal sinusitis, being a rare complication from FS [15].
The main clinical manifestations are from ocular origin and proptosis, chemosis, ptosis or diplopia are common features.
The presence of filling defects representing the occluding thrombus is demonstrated on either CT or contrast-enhanced MRI, although MRI is considered superior [13].
Cavernous sinus thrombosis has a mortality rate of 8 % in children and up to 30 % in adults [4], and may account for important morbidity associated with damage of structures that traverse or are in close relation with the cavernous sinus, including cranial nerves I, III, IV, V1, V2 and VI, internal carotid artery, ophthalmic veins and the optic chiasm [15].
Regarding treatment, aggressive medical therapy and drainage of the affected sinus is indicated [4].
INTRACRANIAL COMPLICATIONS
Except for cavernous sinus thrombosis, the frontal sinus is the most frequent origin site of intracranial complications [13].
The sinus infection can extend to the intracranial compartment directly through bony dehiscence or by means of osteitis [4,19].
In contrast to CT, MRI performs better in the detection, localization and characterization of intracranial collections as well as parenchymal changes, allowing for earlier diagnosis of these complications and a more accurate and reliable distinction between them [4].
Intracranial complications can occur at any age, although more frequent in the second and third decades [2]. Clinical manifestations include severe headache, photophobia, seizures, or focal neurologic findings.
Treatment of intracranial complications requires aggressive medical treatment, and almost invariably, endoscopic sinus surgery, that may be allied with neurosurgical intervention in some severe cases [7].
Epidural empyema
Also known as extradural abscess, it results from the accumulation of pus between the skull and the dura-mater, mostly caused by contiguous infection spread from the adjacent bone. It is almost exclusively derived from frontal sinusitis, due to the poor adhesion of the dura onto the frontal bone posterior wall. Although extradural by definition, it should be noted that epidural empyema frequently occurs in association with or immediately previous to the development of a subdural empyema [16].
Clinically, it courses with mild symptoms, headache and fever, with minimal or absent neurological symptoms, as the dura mater is still acting as a barrier between the infection and the brain parenchyma [4].
As epidural empyema is frequently associated with frontal bone osteomyelitis CT and/or MRI should also include careful evaluation of the overlying tissues, for the presence of abscesses, such as Pott’s puffy tumor, or cutaneous fistulas. Meticulous evaluation of the underlying meninges is essential to identify signs of meningitis. Although dura mater functions as a natural barrier, cerebral edema can be present due to mass effect [4].
Treatment generally comprises drainage of the abscess by craniotomy or transfrontal route and intravenous antibiotherapy [20].
Subdural Empyema
Subdural empyema consists of purulent content located between the dura and arachnoid. It represents 10 % of intracranial complications of sinonasal origin and is frequently caused by frontal sinusitis, followed by ethmoidal and sphenoidal sinusitis [4]. The progression of infection occurs mainly by thrombophlebitis of the emissary veins [17].
In contrast to epidural empyema, there is no dura acting as a barrier between the infectious process and the brain itself. Moreover, retrograde phlebitis can reach and obstruct the cortical veins, leading to edema and infarction, and originating a direct route for the infection spreading [4]. Thus, subdural empyema is considered a neurosurgical emergency, characterized by rapid progression, that ultimately may result in cerebral abscess formation [17,20].
Clinically, there is a rapid deterioration of the patient’s neurologic status, with high fever, headache, neck stiffness, focal neurological deficits, and, more seldomly, seizures [3].
Clinical symptoms overlap with those of meningitis, thus imagiological evaluation is mandatory to detect extra-axial fluid collections [17].
When a subdural empyema is diagnosed, immediate intervention should be performed with drainage of both the empyema and the involved sinuses, in order to prevent or restrict cortical damage as well as neurologic deficits [20].
Antibiotherapy with CSF penetration is the mainstay of treatment and should be promptly started, and subsequently adjusted according to bacterial culture and antibiotic susceptibility test results. Mortality ranges from 20 to 35 %, with lower rates in children [19,20].
Cerebral Abscess
In this case, the purulent collection is located within the brain parenchyma and is either caused by contiguous extension from an infected sinus or by hematogenous spread [4]. Between 14 to 34 % of cerebral abscesses in adults have sinonasal origin, most often due to frontal and, to a lesser degree, sphenoidal sinusitis [3]. This complication is rarer in children, probably due to the underdevelopment of both frontal and sphenoid sinuses [5]. The frontal lobe is the most commonly involved, given its proximity to the frontal sinuses [20].
In the first stages of abscess formation, patients may not present with neurologic symptoms [3]. The early stages of cerebral edema and cerebritis usually manifest as headache, lethargy, agitation, and altered mental status, with progressive worsening of the mental status [7].
Diagnosis is attained by CT or MRI (Figure 3). Lumbar punction should be avoided in the presence of intracranial hypertension [4].
Figure 3. Frontal lobe abscess [green arrow] with perilesional edema, causing mass effect with midline shift.
Treatment varies according to the patient’s status as well as the size and location of the abscess. Small abscesses have been reported to resolve with medical therapy alone. Larger abscesses require stereotactic aspiration or craniotomy with complete excision [3,4].
Besides abscess drainage, treatment includes antibiotherapy and drainage of the involved sinuses. Intravenous treatment should be maintained for 2 to 4 weeks [4].
The initial phase of cerebritis can be treated conservatively and medical therapy should include corticosteroids, anti-intracranial hypertension measures and anticonvulsants [18].
The high mortality rate that ensued some years ago has now decreased considerably to 5 %, due to advances in diagnosis that allow early recognition. Epilepsy is the most common sequel and occurs in 30 % of cases [4].
Meningitis
In the pre-antibiotic era, meningitis was considered the most common complication of rhinosinusitis, but its frequency has decreased in relation to other intracranial complications [2].
The most frequently implicated sinuses are the frontal, sphenoid, and posterior ethmoid.
Clinically, the most important symptoms are headache and neck stiffness, with drowsiness and delirium preceding coma. Diagnosis is established by lumbar puncture, which demonstrates high leucocyte and protein counts [4].
Imaging findings of meningitis are usually nonspecific and difficult to recognize on CT. As for other intracranial complications, MRI is the most suitable imaging modality but findings depend on the stage of disease and may be initially normal [13].
Regarding the treatment of sinusitis in the setting of meningitis, clinical judgment determines whether initial treatment is medical or surgical. Systemic antibiotics with good cerebrospinal fluid penetration are critical in either situation and should be started immediately, with a third generation parenteral cephalosporin and metronidazole in association with intravenous corticosteroid being the most recommended for empiric therapy [3]. If medical therapy fails to improve the patient's condition in 24 to 48 hours, progressive surgical intervention should be considered for the underlying sinusitis [20].
Limitations of this study. This review was limited by the fact that the search was performed in only one database, in only two languages. These factors restrain the scope of this review.
CONCLUSIONS
Complications of frontal sinusitis can be severe and life threatening, mainly due to the proximity of the frontal sinus with the intracranial compartment.
Due to its high availability, CT frequently is the first imaging technique performed in the emergency setting. The excellent bone and high-spatial resolution make CT the preferred imaging examination in presurgical planning. However, contrast-enhanced MRI is far superior in soft-tissue evaluation and should be considered whenever an orbitary or intracranial complication is suspected.
These complications are mostly treated with intravenous antibiotics and surgical drainage procedures.
Early aggressive intervention has decreased morbidity and shortened hospital stay, although significant morbidity and mortality from complications can still occur.
