Sinonasal Schwannomas: Imaging Findings and Review of Literature

Abstract

Objective

Schwannomas are common nerve sheath tumors and may occur anywhere in the body. 4% of head and neck schwannomas occur in the sinonasal cavity, and fewer yet have an intracranial component, making these presentations extremely rare. Furthermore, schwannomas present with nonspecific imaging signs and can only be definitively differentiated via histopathologic review, leading to misdiagnosis as various nasal tumors. We aim to conduct a review of published literature on sinonasal schwannomas with and without intracranial extension and provide additional case representations.

Methods

A literature review was conducted using the PubMed Database with the terms “sinonasal schwannoma,” “intracranial,” “anterior skull base,” and “schwannoma.” Results were reviewed, and additional cases identified were referenced and included in the study. Inclusion criteria were any case with intracranial extension of the schwannoma. There were no exclusion criteria. Review data was compiled into Excel and used for data analysis and comparison. Additionally, a search was done within our institution to identify additional cases of sinonasal schwannoma.

Results

We identified 17 cases of sinonasal schwannoma with intracranial extension, five from our institution and twelve from literature. Analysis revealed: 8 females (47%), 9 males (53%), 9 patients presented with headaches (53%), 6 patients presented with anosmia (35%), 4 patients presented with nasal obstruction (24%), and 2 patients with no symptoms (12%). Mean age and median were 39.4 ± 10.1 and 40, respectively. For treatment, 4 patients underwent endoscopic resection (24%), 11 underwent craniotomy (65%), and data was unavailable for 2 patients. Post-treatment complications occurred in 6 patients, 5 had CSF leaks (29%) and 1 had a hematoma (6%).

Conclusion

We identified and discussed 17 cases of sinonasal schwannoma with intracranial extension. We hope our review provides insight for clinicians to maintain schwannoma as a potential differential when evaluating nasal and anterior skull base masses.

Introduction

Schwannomas are slow-growing and benign tumors thought to arise from Schwann cells, which are responsible for the myelination of nerve fibers. While schwannomas may occur anywhere in the body, roughly 25–45% of all schwannomas occur in the head and neck region, the most commonly affected location being the vestibulocochlear nerve. ¹ Sinonasal schwannomas account for 4% of all head and neck schwannomas, with fewer than one hundred reported cases.^1-3 The clinical presentation of sinonasal schwannomas is generally variable and nonspecific due to tumor location and indolent course. Additionally, when schwannomas extend intracranially, there is considerable overlap with more common entities. Some patients are asymptomatic and diagnosed after workup of incidental findings on imaging. When present, symptoms can vary from anosmia, nasal obstruction, epistaxis, headaches, visual disturbances, and fullness.^2,4-6 This review tries to elucidate characteristic features of sinonasal schwannomas, however, the findings are nonspecific. Our set of cases demonstrates that schwannoma must be on the differential for a sinonasal or anterior skull base mass. We consider an additional 6 cases ranging in size and presentation.

Methods of Review

A thorough review of published literature was done to identify additional cases of sinonasal schwannomas with intracranial extension, done via a search of the “PubMed” database. First, a simple search was conducted for “sinonasal schwannoma” and “intracranial.” Following this, another search was done for “anterior skull base” and “schwannoma.” Relevant articles and their references were reviewed, and additional articles of interest were gathered from them. The inclusion criteria for the review were any cases that had sinonasal schwannomas with an intracranial extension. All statistical analysis was done in Excel. Our review identified twelve reported patients with an intracranial extension of sinonasal schwannomas (Table 3).

Patients and Results

Our cohort consisted of 6 patients who presented to our institution between 2003 and 2022. Out of the 6 patients found with sinonasal schwannoma, five were confirmed to have intracranial extension. Five out of six patients endorsed nonspecific symptoms such as headache and nasal obstruction, and one patient was diagnosed purely incidentally. Among the patients included, 66% were female, and ages ranged from 40 to 65 years old. MRI and CT findings were also nonspecific, resulting in biopsy and histopathologic diagnosis of schwannoma in all 6 patients. Four out of six patients underwent trans-nasal endoscopic resection, one required frontal craniotomy, and one was lost to follow-up with no treatment. One patient experienced a post-surgical CSF leak which was repaired. In follow-up, no patient experienced a recurrence of schwannoma. The cases are summarized in Table 1.

Table 1.

Summary of Schwannoma Cases Presenting to Our Institution Beginning in 2003(ER: Endoscopic Resection) (Figures 1 and 2).

Case	Age at presentation	Sex	Presenting complaint	Location	Treatment	Intracranial component?
1	59	F	Headache, Fullness	Olfactory Groove	ER	Yes
2	58	M	Headache, Sinusitis	Left Ethmoid	ER	Yes
3 (Imaging Unavailable)	33	F	Nasal Obstruction	Ethmoid	ER	Yes
4	49	F	Dizziness, Nonspecific Neurologic	Ethmoid	Craniotomy	Yes
5	64	F	None	Unknown	None	No
6	43	M	Headaches, Incidental finding	Ethmoid, Anterior cranial fossa	ER	Yes

When added to the reported cases in existing literature, the results are as follows: 8 out of 17 cases were female (47%,), 9 out of 17 cases were male (53%), 9 out of 17 patients presented with headaches as the primary symptom (53%), 6 patients presented with anosmia (35%), 4 patients presented with nasal obstruction (24%), and 2 patients had no symptoms, and the mass was found incidentally (12%). The mean age of the 17 patients was 39.4 ± 10.1, and the median was 40. The most common origin location seen was the ethmoid sinus. For treatment, 4 patients underwent endoscopic resection (24%), 11 underwent craniotomy (65%), and treatment data was unavailable for 2 patients. Post-treatment complications occurred in 6 out of the 17, with 5 having CSF leaks (29%) and 1 having hematoma post craniotomy (6%).

Discussion

Schwannomas are tumors of the peripheral nervous system most commonly arising from tumorigenic Schwann cells, which are responsible for the myelination of nerve fibers. They are usually sporadic; however, about 5% of schwannomas occur in relation to the Neurofibromatosis Type 2 mutation.^3,7,8 The leading theory on the origin of sinonasal schwannomas is that they arise from the ophthalmic and maxillary branches of the trigeminal nerve or nasal autonomic nerves. ⁹ Based on our review, there are twelve documented cases of sinonasal schwannomas with intracranial extension, and our series describes an additional five cases, bringing the total to seventeen in published literature (Table 3). Schwannomas have been shown to arise from Schwann cells but more recently have been thought to involve injury to many cell types such as axons, macrophages, T cells, fibroblasts, extracellular matrix, and blood vessels. ⁷ Schwannomas tend to occur in areas where the nerve is prone to injury or undue stress, such as the trigeminal nerve, which is confined during its course.^7,8 While mostly benign tumors, they do have the potential to become malignant. As they grow larger, schwannomas remodel surrounding tissue and bone, leading to invasion of adjacent spaces such as the anterior skull base (Figures 1 and 2).

Figure 1.

Panel 1. (A–B): Case 1, Homogenously enhancing mass in the right anterior ethmoidal sinus and nasal cavity, extending into the right orbit and anterior cranial fossa. (C): Case 2, Homogenous mass involving the right nasal cavity and anterior ethmoid sinuses with erosion of the cribriform plate and intracranial extension. (D–E): Case 4, Heterogeneously enhancing nasoethmoidal mass with intracranial extension abutting the inferior surface of the frontal lobe. [White Arrows].

Figure 2.

Panel 2. (A–B): Case 5, Lesion involving the posterior nasal cavity extending into the sphenopalatine foramen. No intracranial extension. (C–D): Case 6, Large multilobulated heterogeneously enhancing mass centered at the level of the anterior skull base, involving the anterior cranial fossa and nasal cavity. [White Arrows] (E–F): Histology of case 6, Compact hypercellular Antoni A areas and myxoid hypocellular Antoni B areas, nuclear palisading around fibrillary process (Verocay bodies) is seen in cellular areas. Hemosiderin deposition can also be seen as brownish deposits (white circle).

Histologically, schwannomas present with 2 distinct architectures: Antoni Type A and Antoni Type B. Verocay bodies are zones lacking any nuclei amidst areas of organized elongated nuclei, a hallmark feature of Type A. Type B, on the other hand, demonstrates an array of cells with no organization amongst loose stroma and lipid vacuoles in a microcystic pattern. Interestingly, the 2 architectures are not exclusive, and Type A may transition into a structure more similar to Type B.^7,8,10 (Figure 2). Schwannoma cells can also be characterized by a + S-100 immunohistochemical stain, further narrowing the differential of nasal tumors. ¹⁰

On CT, the schwannomas appear isodense to the brain with moderate enhancement with contrast. Intratumor cystic areas, if present, are hypodense and can help differentiate them from other masses such as esthesioneuroblastomas. MRI findings on T1 reveal iso- to hypointense masses with prominent heterogeneous enhancement and T2 hyperintensity. Furthermore, on T2*, hemosiderin deposition can be visualized in some schwannomas offering a critical diagnostic clue (Figures 1 and 2).^11-14

Due to their unusual location and rarity, sinonasal schwannomas are low on the differential diagnosis of masses in the anterior skull base or nasal cavity. Many lesions have overlapping nonspecific symptoms, including esthesioneuroblastoma (ENB), adenocarcinoma, sinonasal undifferentiated carcinoma (SNUC), squamous cell carcinoma, inverted papilloma, sinonasal neurofibromas, and olfactory ensheathing cell tumors (OECT).^14-16 While radiographic clues may help with clinical differentiation, diagnosis hinges on a tissue biopsy. Of note, OECT and sinonasal neurofibromas are challenging to differentiate from schwannoma since all are S-100+ and have similar radiologic features. Specialized immunostaining can aid in a more accurate diagnosis.^3,10

We organized a blinded read study with three expert neuroradiologists to evaluate the top differential diagnosis in our cases of interest. The results are shown in Table 2. Survey findings reveal a common confusion distinguishing an anterior skull base mass as ENB or a schwannoma. Whereas schwannomas are usually benign, ENBs are malignant tumors arising from the neuroepithelium of the nasal cavity. ENB and schwannoma are both slow-growing, indolent masses that remodel surrounding bone.^17,18 Although not always present, ENBs may be uniquely identified on imaging by the presence of peritumoral cysts and calcifications. Ultimately, differentiation between a schwannoma and an ENB relies on a histopathologic analysis, where ENB shows primitive neuroblastoma cells in a dense neurofibrillary background.^14,18-20 Additional confusion was also seen with SNUC and inverted papilloma. On imaging, an inverted papilloma typically has lobulated borders and a cerebriform appearance on MR imaging, while SNUC is a more aggressive tumor that causes destruction of the bone; however, this is a nonspecific sign, and diagnosis also relies on histopathologic confirmation.^15,21

Table 2.

Summary of the Top Differentials Given by 3 Independent Expert Neuroradiologists. They Were Blinded to the Patient History and Presentation.(Figures 1 and 2)

	Blind reader 1	Blind reader 2	Blind reader 3
Case 1	Schwannoma	Schwannoma	Schwannoma
Case 2	Esthesioneuroblastoma	Mucocele	Mucocele
Case 3 (imaging unavailable)
Case 4	SNUC	Natural killer cell lymphoma	SNUC
Case 5	SNUC	Inverted papilloma	Inverted papilloma
Case 6	Schwannoma	Schwannoma	Schwannoma

Treatment for schwannomas consists of endonasal resection, with frontal craniotomy when needed.^5,22 Potential treatment complications include graft failure and CSF leaks, as observed in one patient described in our series, but more prevalent in the literature review (Table 3).

Table 3.

Summary of Sinonasal Schwannomas with Intracranial Extension as Described in the Literature. Presenting Symptoms of Sinonasal Schwannomas are Generally Nonspecific, Such as Headache and Anosmia, Similar to the Patients Described in Our Cohort.

Author	Year	Age	Gender	Clinical features	Surgical approach	Complications
Zovickian et al. 23	1986	40	M	Headache, nasal obstruction	Frontal craniotomy	None
Enion et al. 24	1991	28	M	Headache	Bifrontal craniotomy	CSF leak
Bavetta et al. 25	1993	41	M	Anosmia, nasal obstruction	Frontal craniotomy	Hematoma
Fujiyoshi et al. 26	1997	38	M	Epistaxis, nasal congestion	Unknown	Unknown
Sharma et al. 27	1998	35	M	Anosmia, epistaxis	Bifrontal craniotomy	CSF leak
Gatscher et al. 28	1998	50	F	Anosmia, headache	Bifrontal craniotomy	Unknown
Siqueira et al. 29	2001	40	F	Anosmia, headache	Bifrontal craniotomy	None
Ogunleye et al. 30	2006	31	F	Anosmia, facial swelling	Unknown	None
George et al. 5	2009	27	F	Headache, blurred vision	Frontal craniotomy	CSF leak
Hong et al. 4	2016	24	M	Asymptomatic	Bifrontal craniotomy	Abscess, CSF leak
Eichberg et al. 6	2017	41	M	Anosmia, headache	Bifrontal craniotomy	None
Narang et al. 2	2019	33	F	Left eye proptosis, Epistaxis	Bifrontal craniotomy	None

Conclusion

Although rare, schwannomas in the sinonasal cavity can be easily misdiagnosed due to their indolent nature and nonspecific presentation. As their size increases, sinonasal schwannomas can extend into and remodel the anterior skull base tissues, leading to neurologic symptoms. We reported five cases of sinonasal schwannoma with extension into the cranium, bringing the total in available literature to seventeen. Our review highlights the fact that one must consider sinonasal schwannomas when evaluating nasal masses, resulting in earlier diagnosis and treatment.