Inverted Papilloma

Inverted papilloma (or Schneiderian papilloma, inverted type), which is included in the group of sinonasal papillomas together with the oncocytic and exophytic variants, is the second most common benign tumor of the sinonasal tract after osteoma, even though it represents the most common surgical indication for a benign sinonasal tumor. The lesion is estimated to represent 0.4% to 4.7% of all surgically removed nasal tumors, with an incidence ranging from 0.6 to 1.5 cases per 100,000 inhabitants per year.^2,3 Men are more commonly affected than women, and the lesion is prevalently observed in the fifth and sixth decades of life.

With regard to the histologic appearance, inverted papilloma is composed exclusively or almost exclusively of hyperplastic ribbons of basement membrane–enclosed epithelium that grow endophytically into the underlying stroma. The epithelium is multilayered and formed of squamous or ciliated columnar cells mixed with mucocytes.⁴

Inverted papilloma most frequently arises from the lateral nasal wall in the fontanelle area. The maxillary sinus is the second most commonly affected site, and frontal and sphenoid sinuses are rarely involved primarily. Often the lesion extensively involves more than one sinus, making it impossible to assess the exact site of origin.

The association of inverted papilloma with squamous cell carcinoma has been overemphasized, with reported frequencies as high as 56%.⁵ Recent data clearly show that the prevalence varies between 3.4%⁶ and 9.7%⁷ and that synchronous occurrence is more common than metachronous.

Inverted papilloma is suspected to have a viral etiology. Human papillomavirus DNA has been demonstrated by in situ hybridization or the polymerase chain reaction in papillomas, with a prevalence of serotypes 6, 11, 16, and 18.^8,9 The last two serotypes have been specifically found to be associated with inverted papillomas that show histologic signs of malignant transformation. Not unexpectedly, in this setting an increase in levels of epidermal growth factor receptor and tumor growth factor-α has been demonstrated.¹⁰

Unilateral nasal obstruction with watery rhinorrhea is the most common symptom prompting the patient to seek otolaryngologic consultation, whereas epiphora, proptosis, diplopia, and headache may be associated with advanced lesions involving the orbit or the skull base. Endoscopy of the nose, usually showing a pale, polypoid lesion with a papillary appearance protruding from the middle meatus (Fig. 49-1), may easily suggest the diagnosis, which is sometimes made less obvious by the concomitant presence of inflammatory polyps. A biopsy performed under endoscopic guidance is indicated to establish the histologic diagnosis.

Figure 49-1. Typical endoscopic appearance of an inverted papilloma. A polypoid lesion with a pale, papillary surface protrudes from the middle meatus and extensively fills the left nasal cavity.

Imaging studies are required to assess the extent and three-dimensional configuration of the lesion and to disclose its relationship with surrounding structures (i.e., orbit, skull base, optic nerve, internal carotid artery). In our experience, these goals are best achieved by MRI with gadolinium enhancement, which also has the advantage over CT of better differentiating tumor from inflammatory mucosal changes and to disclose the so-called cerebriform-columnar pattern (Fig. 49-2). This reflects the histologic arrangement of inverted papilloma characterized by the alternation of regular parallel folds made of a highly cellular metaplastic epithelium and of an underlying less cellular stroma. It is therefore highly predictive for inverted papilloma diagnosis.¹¹ However, even MRI has limitations, especially in lesions completely filling the maxillary, sphenoid, or frontal sinus, in differentiating inverted papillomas growing inside the sinus but arising from a small area of insertion from those extensively involving the mucosa. Recent studies indicate that focal hyperostosis¹² and osteitic changes¹³ upon CT may be considered reliable predictors of tumor origin. These findings may also be identified by MRI (Fig. 49-3).

Figure 49-2. Inverted papilloma on an axial contrast-enhanced, T1-weighted, spin-echo magnetic resonance image. The maxillary sinus is occupied by a solid mass protruding into the nasal fossa through an accessory ostium. The lesion exhibits a cerebriform-columnar pattern, which is typically seen in inverted papilloma (arrows).

Figure 49-3. Inverted papilloma on a magnetic resonance (MR) image and a computed tomography (CT) scan, both in the coronal plane. The maxillary sinus is completely occupied by an expansile lesion that destroyed the medial wall and invaded the right nasal fossa. A, The T2-weighted spin-echo MR image demonstrates the cerebriform-columnar pattern of the lesion and permits visualization of the bony spur along the lateral maxillary sinus wall where the lesion originates. B, The CT scan does not provide a good characterization of soft tissue density opacification but gives a superior view of the sclerotic bony spur.

As clearly shown by a 2006 meta-analysis¹⁴ and by our experience based on 300 inverted papillomas, endoscopic surgery is a reliable alternative to traditional external techniques for the vast majority of lesions. An exclusive endoscopic approach may be contraindicated in the following situations: (1) massive involvement of the mucosa of the frontal sinus and/or of a supraorbital cell, (2) intradural extension or transorbital extension, both of which are very uncommon situations usually found in patients who have already undergone one or more surgical procedures, (3) concomitant presence of a malignancy involving critical areas, and (4) presence of abundant scar tissue from previous surgery.

One criticism of endoscopic approaches is the impossibility in always obtaining an en bloc resection. However, it is not the concept of en bloc resection per se that has to be fulfilled to achieve complete removal; the key point is to dissect the involved mucosa along the subperiosteal plane and to drill the underlying bone whenever required by imaging and/or intraoperative findings.¹⁵ The extent of the operation is dictated by the site of the lesion and the area of mucosa involved by the lesion. Apart from cases with a clearly identifiable small attachment of the lesion, which can be managed with a very conservative approach,¹⁶ there are basically three different types of endoscopic resections available, according to our classification.¹⁷ Type I resection (Fig. 49-4A) is indicated for inverted papillomas involving the middle meatus, ethmoid, superior meatus, sphenoid sinus, or a combination of these structures; even lesions protruding into the maxillary sinus without direct involvement of the mucosa are amenable to this approach. Type II resection (Fig. 49-4B), which corresponds to an endoscopic medial maxillectomy, is indicated for tumors originating within the nasoethmoidal complex and secondarily extending into the maxillary sinus or for primary maxillary lesions not involving the anterior and lateral walls of the sinus itself. The nasolacrimal duct can be included in the specimen to increase the exposure of the anterior part of the maxillary sinus. Type III resection (Fig. 49-4C), also known as the Sturman-Canfield operation or endonasal Denker operation,¹⁸ entails removal of the medial portion of the anterior wall of the maxillary sinus to enable access to all the antrum walls. It is therefore recommended for inverted papillomas extensively involving the anterior compartment of the maxillary sinus.

Figure 49-4. Schematic drawings summarizing the different endoscopic resections used for inverted papillomas of the naso-ethmoid-maxillary region. A, type I resection; B, type II resection; C, type III resection. See text for explanation.

Frontal sinus involvement can be observed in different scenarios, ranging from a limited lesion marginally growing from the ethmoid into the frontal recess (Fig. 49-5) to very complex cases in which most or all of the sinus mucosa is diseased. Because the key point for ultimate success is removal of the lesion along the subperiosteal plane with the possibility to drill out the underlying bone, the surgical choice may involve a Draf IIB or Draf III endoscopic sinusotomy or a combination of an endoscopic approach with external sinusotomy through an osteoplastic flap depending on the extent of frontal sinus mucosa involvement, a finding that can usually be definitively assessed only at the time of surgery. Even the involvement of an extensively pneumatized supraorbital cell is frequently challenging. Exposure through the nose may be increased by coagulation and sectioning of the anterior ethmoid artery and by displacement of the orbit after drilling of the upper portion of the lamina papyracea. However, whenever the lesion involves a cell that extends far posteriorly and/or laterally over the orbit and complete resection cannot be achieved transnasally, the surgeon should resort to a frontal osteoplastic flap.

Figure 49-5. Inverted papilloma on a sagittal contrast-enhanced magnetic resonance image. The advantage of this acquisition plane is the excellent assessment of tumor growth into the most caudal part of the frontal sinus. The upper part of the sinus is filled with inflammatory secretions (asterisk). The sagittal plane also permits accurate evaluation of the relationships between the tumor and the floor of the anterior cranial fossa, which is not invaded (arrow).

Regardless of the access selected for inverted papilloma resection, the operation should end with the creation of a largely marsupialized cavity that will give wide access during follow-up for endoscopic inspection, which should be periodically performed in order to diagnose residual or recurrent lesions early. Postoperatively, MRI or CT is indicated only when a sinus that was originally involved by the lesion is not accessible for exploration owing to scar closure, the patient is symptomatic, or a residual or recurrent lesion has been histologically documented.

In the era when transnasal resection without endoscopic or microscopic assistance was the most commonly used technique, the rate of recurrences ranged from 40%¹⁹ to 78%.²⁰ These extremely high values indicate that these “recurrences,” mostly occurring at the site of primary resection, should have been more appropriately regarded as residual lesions. They reflected the inadequacy of transnasal surgery in affording a radical excision of the lesion. In view of such limitations, medial maxillectomy through lateral rhinotomy was established in the 1970s and 1980s as the gold standard for treatment of inverted papilloma. Although the frequency of recurrences decreased, reportedly from 0%²¹ to 29%,²² this technique was associated with potential aesthetic sequelae. Therefore, midfacial degloving became the most popular approach for the management of inverted papilloma. The routine use of available staging systems specific for inverted papilloma^23–27 would facilitate the comparison of results among different institutions.

Juvenile Angiofibroma

Juvenile angiofibroma is a benign lesion histologically characterized by vascular endothelium–lined spaces embedded in a fibrous stroma that typically affects young male adolescents. Immunohistochemical and electron microscopy studies suggested that the lesion could be considered a vascular malformation (or hamartoma) rather than a tumor.²⁸ These observations led Schick and colleagues²⁹ to postulate that juvenile angiofibroma might develop from incomplete regression of a branchial artery, which arises in embryogenesis between day 22 and 24 and forms a temporary connection between the ventral aorta and dorsal aorta. This artery commonly regresses and forms a vascular plexus that either involutes or may leave remnants, potentially leading to development of juvenile angiofibroma (Fig. 49-6). This theory is supported by the finding that juvenile angiofibroma vessels express laminin α₂, which is considered a marker for early angiogenesis.³⁰

Figure 49-6. Schematic drawing summarizing the theory postulated by Schick and colleagues²⁹ on the origin of juvenile angiofibroma (JA) from remnants of the branchial artery. A, During embryogenesis the sixth branchial arch arteries temporarily connect the ventral and dorsal aortas. B, Physiologic regression of several vascular structures (white vessels) subsequently occurs, leading to definitive configuration of the vascular system. C, Regression of the first branchial arch artery takes place via the formation of a vascular plexus, which is usually complete at birth. Incomplete regression of this structure can explain the typical blood supply for juvenile angiofibromas, from the maxillary and sphenopalatine arteries, with persistent vascular connections to the internal carotid pathway. I through VI, six branchial arteries; ECA, external carotid artery; ICA, internal carotid artery.

The lesion has a pathognomonic epicenter of origin at the level of the pterygopalatine fossa and subsequently grows through different pathways of spread that typically follow foramina and fissures of the skull base. The bone may be involved basically with two mechanisms, resorption by pressure coming from subperiosteal growth or invasion of the cancellous component initially at the level of the root of the pterygoid process, with subsequent expansion within the greater wing and erosion of the floor of the middle cranial fossa. In its early phase, juvenile angiofibroma extends through the sphenopalatine foramen into the nasopharynx and the nasal cavity and along the vidian nerve into the floor of the sphenoid sinus. Lateral extension through the pterygomaxillary fissure leads to invasion of the infratemporal fossa, which in advanced lesions may be completely filled. When the lesion expands anteriorly, the posterior wall of the maxillary sinus is progressively pushed forward. Although benign, juvenile angiofibroma may extend intracranially through the orbit via the inferior and superior orbital fissure or along the maxillary nerve to the parasellar region. Encroachment upon the anterior skull base through the ethmoid is less commonly observed. Regardless of the site and pattern of intracranial involvement, transdural growth of the lesion is very rare.³¹

Unilateral nasal obstruction and epistaxis are the most common heralding symptoms of small to intermediate-size juvenile angiofibromas. In advanced lesions, swelling of the cheek, proptosis, or headache may be present, indicating an involvement of the infratemporal fossa, the orbit, or the cranial fossa, respectively. The endoscopic finding of a smooth, hypervascularized lesion originating behind the middle turbinate, which is usually laterally displaced against the lateral wall (Fig. 49-7), in a teenage boy strongly suggests a diagnosis of juvenile angiofibroma, which is usually confirmed by CT and MRI. Therefore, resorting to a biopsy, which is associated with a high risk of hemorrhage, is rarely if ever justified.

Figure 49-7. Juvenile angiofibroma. On endoscopy, the lesion typically appears as a polypoid hypervascularized mass bulging from the lateral wall behind the middle turbinate, which is laterally compressed. The choana is completely obstructed.

On CT and MRI the diagnosis of juvenile angiofibroma is based on the following three features: the area of origin invariably located at the level of pterygopalatine fossa, its hypervascular appearance after contrast enhancement, and its pattern of growth.³² On MRI, the presence on both T1- and T2-weighted sequences of several signal voids within the lesion, indicating major intralesional vessels, further corroborates a diagnosis of juvenile angiofibroma. Sometimes differentiation of this lesion from lobular capillary hemangioma, hemangiopericytoma, and schwannoma can be difficult in view of a similar pattern of enhancement. However, these other lesions do not commonly involve the pterygopalatine fossa and occur in a different age group.

Intraoperative bleeding has always been considered one of the most challenging issues in the management of juvenile angiofibroma, leading in the past to a high rate of persistent disease and to a notable morbidity. The introduction in the early 1970s of preoperative embolization,³³ which is commonly performed 48 hours before surgery, has revolutionized the treatment of this lesion by dramatically decreasing intraoperative bleeding and therefore making the assessment of tumor borders at dissection more accurate. Nowadays, the availability of intra-arterial digital subtraction angiography, microcatheters, and embolic agents such as polyvinyl-alcohol particles makes superselective embolization of feeding vessels even easier.³⁴ Furthermore, angiography provides a detailed map of the lesion’s vascular supply, showing connections with the internal carotid artery, the vertebral artery, and branches of the contralateral carotid system. Although the currently available methods of embolization provide excellent devascularization of feeding vessels from the internal maxillary artery and its branches as well as from the ascending pharyngeal artery, control of major vascularization from the internal carotid artery is demanding. Devascularization by direct tumor puncture and embolization is associated with an unacceptable risk of major neurologic complications³⁵ and has therefore been abandoned. In case of encasement of the internal artery, which is indeed a very rare event, a balloon occlusion test and sacrifice of the internal carotid artery or, as a less invasive procedure, stenting of the intratemporal carotid artery³⁶ may be considered.

Not all authorities concur about routinely performing preoperative embolization. In fact, the modifications induced by this procedure at the tumor periphery have been shown to increase the likelihood of leaving residual tissue behind.³⁷

Several classification systems for juvenile angiofibroma are available in the literature.^38–41 They should be used with the intent to stratify cases according to lesion extent and to make comparison among different series easier.

Surgery is considered the mainstay in the management of juvenile angiofibroma. Several approaches are currently available, ranging from microendoscopic techniques to midfacial degloving and infratemporal fossa resection. Independent of the technique selected, the key steps to minimizing bleeding and achieving radical resection are the dissection of the lesion in the subperiosteal plane with the help of bipolar coagulation and an extensive drilling of the basisphenoid where the tumor is growing with digitations that are difficult to identify even under magnification. The importance of this latter surgical step has been emphasized by Howard and associates,⁴² who have observed a dramatic reduction of recurrences in their series with the systematic removal of the cancellous bone of the sphenoid involved by the lesion.

Endoscopic surgery has also emerged as a viable alternative to traditional external approaches in the management of small to intermediate size juvenile angiofibroma.^43–45 Involvement of the infratemporal fossa, orbit, and parasellar region cannot be considered contraindications to endoscopic surgery (Fig. 49-8), but advanced lesions with extensive involvement of the cavernous sinus or encasement of the internal carotid artery (Fig. 49-9) are better treated through a combined endonasal-external approach. Midfacial degloving or an infratemporal fossa approach may be selected according to the location of the intracranial component and the surgeon’s preference. For lesions with a large intracranial extension, another option is resecting the extracranial component and the intracranial component in two sessions. For residual lesions involving critical areas, the possibility of switching to a combined procedure should always be discussed with the patient, in view of possible scarring that makes dissection through an exclusively endonasal approach problematic. One should also keep in mind that radiotherapy at a low dose (30-36 Gy) has been demonstrated to be effective in cases of advanced or recurrent lesions deemed not amenable to complete resection with acceptable morbidity.⁴⁶ The availability of new techniques such as Gamma knife radiosurgery⁴⁷ and the Cyberknife system⁴⁸ might be alternatives with a low morbidity when used for lesions of limited size.

Figure 49-8. Juvenile angiofibroma on coronal contrast-enhanced magnetic resonance (MR) images obtained before and after endoscopic resection. A, Pretreatment image shows encroachment of both the floor and lateral wall of the left sphenoid sinus and infratemporal fossa. Intracranial extension is demonstrated in close proximity to the superior orbital fissure (arrows). B, MR image obtained after surgical resection shows solid tissue (arrows) along the lateral sphenoid sinus wall; the lack of contrast enhancement suggests residual scar tissue.

Figure 49-9. Juvenile angiofibroma on axial T2-weighted, spin-echo magnetic resonance image. The lesion invades the left orbital apex (OA), the lateral wall of the left sphenoid sinus (white arrows) is completely destroyed, and the internal carotid artery (ICA) is encased. On the right side, a bony barrier (arrowheads) still separates the lesion from the internal carotid artery.

Postoperative surveillance is based on periodic endoscopic and imaging examination. However, because most of the residual lesions tend to grow submucosally, contrast-enhanced CT or MRI plays a key role in their early detection. Imaging studies performed in the immediate postoperative period would identify residual juvenile angiofibroma tissue more easily, because of the absence of any inflammatory changes.⁴⁹ The actual frequency of residual lesions, although difficult to assess, ranges from 6% to 39%.⁴⁷ Even though there is a great variability in postoperative surveillance with respect to the timing and imaging techniques used by different investigators, most residual lesions are diagnosed within 1 year after surgery. Independent of the surgical approach used (external vs. endoscopic), invasion of the sphenoid or pterygoid process, involvement of the infratemporal fossa, foramen lacerum, and/or cavernous sinus in more advanced lesions have a negative impact on local control.⁴¹ Endoscopic surgery, when appropriately planned, is associated with a low rate of residual lesions, which are reported in 6.6%⁴³ to 17%⁴¹ of patients.

Because the understanding of the biologic behavior of residual lesions is still limited, we commonly monitor residual lesions with MRI to assess their pattern of growth. Treatment, in the form of surgery or radiotherapy, is scheduled only when there are clear signs of constant increase in size.

Osteoma

Osteoma, a benign, slow-growing osteoblastic lesion, is the most common benign tumor of the sinonasal tract. It is found in 1% of subjects undergoing plain sinus radiographs and in 3% of those undergoing CT for sinus symptoms.⁵⁰ Osteomas are generally diagnosed between the second and fifth decades of life, with a slight male preponderance commonly reported in the literature. The frontal sinus is the most frequently involved anatomic site (approximately 80% of cases), followed by the ethmoid, the maxillary sinus, and, more rarely, the sphenoid sinus. Osteomas can be observed in conjunction with Gardner’s syndrome, a genetic disorder characterized by multiple polyps of the colon in association with osteomas of the skull and multiple soft tissue tumors.

Macroscopically, most osteomas appear as hard, white, multilobulated masses. The area of origin is easily recognizable in small lesions, whereas in large osteomas its identification can be problematic.

According to the Fu and Perzin⁵¹ classification, osteomas are histologically divided into the following three categories:

There is no general agreement on the mechanisms leading to the development of osteomas. Three main theories have been proposed. The embryologic theory, which proposes that osteoma develops at the junction between the embryonic cartilaginous ethmoid and the membranous frontal bone, does not explain the occurrence of osteomas distant from the area where the frontal bone and the ethmoid labyrinth join together. The traumatic theory correlates the development of osteoma with a previous trauma, whereas the infective theory is based on the belief that local inflammation may alter adjacent bone metabolism by activating osteogenesis.³² One additional possibility is that the etiology of osteomas is variable and the lesions should be more properly considered slow-growing osseous hamartomas arising in childhood.⁵²

Most osteomas are asymptomatic and are occasionally diagnosed during radiographic examinations performed for unrelated reasons. In its more typical frontal or frontoethmoidal localization, an osteoma may interfere with sinus drainage and therefore cause a sinusitis or even a mucocele, with consequent frontal pain. If the lesion involves the outer table of the frontal bone, the patient may complain of aesthetic deformity, whereas tumors growing toward the orbit can cause orbital or lacrimal symptoms (i.e., proptosis, diplopia, orbital pain, epiphora, decreased visual acuity, and even transient blindness). Osteomas extending into the anterior cranial fossa carry the risk of cerebrospinal fluid leak, pneumocele, meningitis, and brain abscess. According to the different patterns of growth, maxillary osteomas impair the sinus drainage, causing symptoms such as pain in the maxillary area, compress the infraorbital nerve and cause neuralgic symptoms, or modify the aesthetic profile of the maxillary region.

Endoscopic examination of the nasal cavity is usually normal, because the lesion is deeply located inside a paranasal cavity. Only in very rare instances in which the osteoma is growing toward the nasal cavity can it be visualized as a firm mass covered by normal or atrophic mucosa.³²

Imaging assessment of osteomas is currently based on CT. According to the amount of mineralized bone within the lesion, osteomas may exhibit a very high density, resembling cortical bone (Fig. 49-10), or a gradually decreasing density to a ground-glass pattern (Figs. 49-11 and 49-12). Contrast enhancement is usually unnecessary to reach a diagnosis.³² Multiplanar reconstructions may help identify the sinus wall of origin of the lesion, which is a relevant finding for selecting the best surgical approach. Whenever the lesion is massively eroding the bony interface with the anterior skull base or the orbit, MRI may better delineate the relationship between the osteoma and adjacent soft tissues (i.e., dura, brain, orbital content).

Figure 49-10. Osteoma on a coronal computed tomography scan. A huge ivory osteoma is shown in the right ethmoid, encroaching on the crista galli and the cribriform plate and invading the anterior cranial fossa. The right orbit is not invaded, and the thin lamina papyracea can still be detected (arrows).

Figure 49-11. Coronal computed tomography (CT) scan showing a frontoethmoid osteoma exhibiting a mixed CT pattern, ivory in the anterior ethmoid and spongiosum into the frontal sinus.

Figure 49-12. Coronal computed tomography scan showing a right ethmoid osteoma that displays a ground-glass density typically seen in the spongiosum variant. The lesion is adjacent to the frontal recess, which is unobstructed (arrows).

Because osteomas are slow-growing, there is general consensus in the literature for a “wait and see” policy for any lesion that is asymptomatic, does not encroach upon critical structures such as the optic nerve (risk for intracranial complication), and is not extensively invading the anterior skull base or the orbit (risk for orbital complication). In this setting, it is advisable to monitor the lesion with periodic cross-sectional imaging examinations, which preferably include MRI. In all other situations, surgery is recommended.

Different external surgical approaches (i.e., frontoethmoidectomy through a Lynch-Howarth incision, midfacial degloving, lateral rhinotomy, Caldwell-Luc procedure, and osteoplastic frontal sinusotomy via a coronal incision) have all been extensively used in the past according to the site and size of osteomas. The introduction and subsequent refinement of microendoscopic techniques led to a revolution in the surgical management of these lesions, and most are now treated through a transnasal approach (video clip available on website). A surgical trick that helps resect even large osteomas through the nose is cavitation, which consists of drilling the core of the lesion with a diamond bur, thus leaving a very thin shell of bone that can be easily fractured and dissected from the adjacent tissues.⁵³ The possibility of using a device inducing ultrasound bone emulsification has also been proposed.⁵⁴ Cerebrospinal fluid leak can be expected during these maneuvers if the lesion is in contact with dura. Consequently, the patient should be informed about this possibility and the need to repair the defect with a multilayer technique.⁵⁵

Schick and colleagues⁵⁶ have precisely established the indications for and limits of endoscopic removal of osteomas. Lesions involving the ethmoid, the sphenoid, the medial wall of the maxillary sinus, and, in some selected cases, even the inferior and medial wall of the orbit can be resected transnasally (Fig. 49-13). Frontal osteomas are amenable to endoscopic surgery if they are located medial to a virtual sagittal plane prolonged upward from the lamina papyracea, if they originate from the inferior portion of the posterior frontal sinus wall, and if the anteroposterior diameter of the frontal sinus is at least 10 mm. Performing a Draf III procedure may sometimes help resect the lateral part of an osteoma of the frontal infundibulum extending over the orbit. However, for lesions extending far laterally in a well-pneumatized frontal sinus, radical removal cannot be achieved with a purely endoscopic procedure (Fig. 49-14). Such a lesion can be completely exposed and drilled out through the combination of an endoscopic approach with an image-guided frontal trephination⁵⁷ or, in more extensive lesions, with osteoplastic flap sinusotomy. In our experience, obliteration of the frontal sinus is contraindicated whenever a large frontal sinusotomy, which can maintain satisfactory sinus drainage, is performed. On the other hand, when a frontal osteoma is located laterally and does not involve the frontal infundibulum, resection is better achieved through an exclusive osteoplastic flap without disturbing the frontal sinus outflow. In the case of a lesion that is massively eroding the anterior wall of the frontal sinus, reconstruction is required to maintain a regular frontal contour. This can be accomplished through the harvest of a split calvarial graft from the parietal bone, which is fixed in place by microplates.

Figure 49-13. On a coronal computed tomography scan, a large ethmoid osteoma can be seen invading the orbit and displacing the optic nerve (ON), the superior oblique muscle (SO), and the inferior rectus muscle (IR). The high and quite homogeneous density is characteristic of the ivory variant. The lesion was resected via an endoscopic approach.

Figure 49-14. An ivory osteoma is shown in the most lateral aspect of the left frontal sinus in this coronal computed tomography scan. The lesion is rather distant from the frontal recess (arrows), which is narrowed by large agger nasi cells (asterisks). The osteoma was managed with a combination of an endoscopic approach with an osteoplastic frontal sinusotomy. ioc, infraorbital cell.

Because osteoma recurrences are very rare, routine periodic postoperative surveillance by CT is not justified. We usually perform CT examination 1 year after surgery and, on the basis of its results, make a decision about further radiologic follow-up. The presence of a symptomatic stenotic frontal or maxillary sinusotomy is another situation calling for CT examination.

Lobular Capillary Hemangioma

Lobular capillary hemangioma is a rapidly growing lesion characterized by a proliferation of capillaries arranged in lobules and separated by a loose connective tissue stroma, often infiltrated by inflammatory cells.⁵⁸ The tumor has been commonly reported in the literature as “pyogenic granuloma,” which is currently considered inadequate in view of the fact that the lesion is neither the result of a bacterial infection nor a true granuloma.

Most mucosal lobular capillary hemangiomas of the head and neck arise in the oral cavity, and fewer in the nasal cavity. In a series of 40 patients reported by Puxeddu and colleagues,⁵⁹ age ranged from 10 months to 72 years, with a mean age of 42 years and a peak incidence in the fifth decade of life. No gender preponderance was observed.

The etiopathogenesis of lobular capillary hemangiomas is still obscure. Trauma, hormonal influences, viral oncogenes, underlying microscopic arteriovenous malformations, and the production of angiogenic growth factors have been all advocated as potential etiopathogenetic factors. The relevance of trauma such as habitual nose picking and nasal packing is supported by the fact that most lesions are located in the anterior half of the nasal cavity at the level of Little’s area or on the head of inferior and middle turbinates.

In its typical presentation, lobular capillary hemangioma appears at endoscopy as a red to purple mass, not larger than 1 cm, associated with epistaxis.⁵⁹ However, in more rare instances the lesion reaches a considerable size, filling the nasal cavity entirely and leading to a complaint of unilateral nasal obstruction. In this setting, differential diagnosis from other hypervascularized lesions, such as angiofibroma, angiomatous polyp, hemangioma, hemangiopericytoma, paraganglioma, angiosarcoma, and metastases from highly vascularized tumors (i.e., kidney or thyroid carcinoma), can be problematic and requires appropriate imaging studies as a first step. On CT, the lesion appears as a unilateral mass with soft tissue density, whereas the MRI pattern consists of T2 hyperintensity and spontaneous T1 hypointensity; on both sequences, vivid enhancement can be observed after administration of paramagnetic contrast medium.³² Once angiofibroma is excluded, because of its peculiar location and epidemiologic profile, only histologic examination may establish a definitive diagnosis.

Surgery is the treatment of choice for lobular capillary hemangioma, and radical resection can be performed through an endoscopic approach even in large lesions.³² In our experience, only in one case was formal anterior craniofacial resection necessary; in that case, the lesion extensively involved the orbit and anterior skull base and was associated with intravascular papillary endothelial hyperplasia (Fig. 49-15).⁶⁰

Figure 49-15. A lobular capillary hemangioma appears on a coronal contrast-enhanced magnetic resonance image as a large ethmoid lesion abutting the orbit and encroaching on the floor of the anterior cranial fossa. The sharp borders of the intracranial part of the lesion and the subtle dural enhancement suggest extradural invasion (arrows).

Ossifying Fibroma and Fibrous Dysplasia

In the past, ossifying fibroma and fibrous dysplasia were traditionally grouped together because of their histologic similarities. In 1963, however, Reed⁶¹ suggested that they should be regarded as two distinct entities. Ossifying fibroma is a true benign neoplasm, whereas fibrous dysplasia is a genetically based developmental anomaly of the bone-forming mesenchyme with a defect in osteoblastic differentiation and maturation that leads to a replacement of normal bony tissue by fibrous tissue of variable cellularity and immature woven bone. The main histologic differences between the two lesions lie in the absence of a capsule and the presence of more immature bone without osteoblastic activity in fibrous dysplasia.⁶² Psammomatoid ossifying fibroma is a variant of ossifying fibroma characterized by the presence of numerous small ossicles in stroma that resemble psammoma bodies found in extracranial meningiomas, which are indeed acellular and test positive for epithelial membrane antigens.⁶³

Ossifying fibroma of the sinonasal tract generally occurs in the third and fourth decades of life, preferentially in black women, whereas its psammomatoid variant typically affects men at a younger age and displays a more aggressive local behavior. Fibrous dysplasia is commonly diagnosed within the first two decades of life and may present in the following three forms: monostotic, polyostotic, and disseminated, the last also known as McCune-Albright syndrome.

Neither ossifying fibroma nor fibrous dysplasia is associated with specific symptoms. However, the former more frequently manifests as a space-occupying lesion in the nasal cavity that is evident at endoscopic examination and causes nasal obstruction, whereas the latter in an advanced stage may interfere with frontal or maxillary sinus drainage resulting in pressure or pain in the corresponding area, compress the optic nerve or the orbit with impairment of the vision or diplopia, respectively, or result in aesthetic deformities. Endoscopic findings are usually unremarkable or, as with osteoma, may consist of a lesion covered by intact mucosa.

The CT appearance of fibrous dysplasia is strictly related to the degree of mineralization of the tissue. In the early phases, associated with a high density of fibrous tissue, the lesion displays a radiolucent or lytic appearance, which is difficult to differentiate from a simple bone cyst. As the amount of bony tissue increases, a ground-glass (Fig. 49-16) or sclerotic appearance is seen. On MRI, the signal is reported as rather variable on T2-weighted sequences, whereas the T1 signal is more commonly hypointense. Nonhomogeneous enhancement may be obtained after gadolinium administration.³²

Figure 49-16. Coronal computed tomography scan showing fibrous dysplasia. An expansile lesion can be seen in the right ethmoid with a mixed density pattern, including calcifications, ground-glass appearance, and low-density areas. This pattern reflects the different degrees of mineralization of the fibrous tissue replacing normal bone. The lamina papyracea is interrupted (arrowheads) but the orbit is not invaded. The cribriform plate is thickened and displays a ground-glass pattern (arrows), suggesting fibrous dysplasia.

Although differentiation on imaging between fibrous dysplasia and ossifying fibroma may be problematic, the latter more commonly appears on CT as a well-defined, multiloculated lesion, bordered by a peripheral eggshell-like dense rim.⁶⁴ On MRI, ossifying fibroma displays a hyperintense signal on T2-weighted sequences, but on T1-weighted sequences, the signal is intermediately intense to hyperintense in the central part of the lesion and hypointense in the outer shell.³²

The objective of surgical treatment is different for the two lesions. Ossifying fibroma requires radical resection, in view of both the high rate of relapses, accounting for 44% of lesions localized in the ethmoids,⁶⁵ and the aggressive behavior of recurring tumors, with local destruction and potential invasion of adjacent vital structures.⁶⁶ Successful removal of ossifying fibroma via an endoscopic approach has been reported in the literature.^67–69 For fibrous dysplasia, surgery is intended to relieve symptoms such as visual impairment due to compression of the optic nerve or to correct aesthetic deformities, but not to remove the entire lesion. Optic nerve decompression has been traditionally achieved through external transfacial, neurosurgical, or combined approaches, although most cases can nowadays be managed with endonasal endoscopic surgery.^67,70–73 Radiotherapy is contraindicated because of the risk of malignant transformation and the possible side effects on facial skeleton growth in young patients.

Medical treatment of fibrous dysplasia based on the use of bisphosphonates (i.e., pamidronate), which inhibit osteoclastic activity, has been used with success in patients with extensive lesions associated with significant disfigurement and pain.^74,75

Schwannoma

Schwannoma is a neurogenic tumor arising from the Schwann cells of the sheath of myelinated nerves. This is a rare neoplasm that can be found in any part of the body; in 25% to 45% of cases, it is localized at the level of the head and neck. Only 4% of the lesions involve the sinonasal tract, where the ethmoid, maxillary sinus, nasal fossa, and sphenoid are involved (listed in order of decreasing frequency). According to a review of 160 cases,⁷⁶ the age distribution ranges from 6 to 78 years, with most patients between 25 and 55 years of age, and no gender preference. The lesion has been only rarely observed in association with von Recklinghausen’s disease.

Sinonasal schwannomas are considered to arise more frequently from the ophthalmic and maxillary divisions of the trigeminal nerves, but they can also originate from sympathetic fibers of the carotid plexus or parasympathetic fibers of the pterygopalatine ganglion. Particularly in large lesions, identification of the nerve of origin at surgery is extremely difficult.

Macroscopically, the tumor appears as a well-delineated but nonencapsulated globular, firm to rubbery yellow-tan mass.⁷⁷ Histologically, schwannomas are composed of cellular Antoni A areas with Verocay bodies and hypocellular myxoid Antoni B areas. Tumor cells are strongly and diffusely immunoreactive for S-100 protein. The pathologist should differentiate schwannoma from neurofibroma, solitary fibrous tumor, leiomyoma, fibrous histiocytoma, and fibrosarcoma.

At endoscopy, the appearance of a sinonasal schwannoma is quite nonspecific; the presence of a network of capillaries on the surface may sometimes suggest a diagnosis of a hypervascular lesion (Fig. 49-17). CT findings are not usually diagnostic, but MRI reflects the histologic features of the lesion (Fig. 49-18). Specifically, lesions with a prevalent Antoni A component have an intermediate signal on both T1- and T2-weighted images, whereas in those with a predominant Antoni B pattern, which is related to a loose myxoid stroma, hyperintensity is observed on T2-weighted images.^78,79

Figure 49-17. This benign schwannoma appears on endoscopy as a large polypoid mass entirely filling the left nasal cavity. A network of capillaries on the surface of the lesion may suggest a diagnosis of hypervascularized tumor.

Figure 49-18. Benign schwannoma on a sagittal T2-weighted, spin-echo magnetic resonance image. A large hyperintense mass obliterates the nasal fossa and protrudes into the sphenoid and frontal sinus. The ethmoid roof is eroded, and the crista galli cannot be recognized. A concomitant hemangioma of the soft palate is also visible.

Radical surgery is the treatment of choice for sinonasal schwannoma. Before the advent of endoscopic surgery, a large variety of external approaches were employed in relation to the site and size of the lesion. After the initial report by Klossek and coworkers⁸⁰ on the endoscopic management of sinonasal schwannomas, other cases with successful outcome have appeared in the literature,^81–83 thus supporting the idea that even for this tumor, endoscopic surgery can be considered a viable alternative to traditional techniques.