Sinonasal Schwannoma Presenting as a Polypoidal Mass of the Posterior Ethmoid and Sphenoid Sinus: A Rare Case Report with Radiological and Histopathological Correlation

Schwannomas are benign encapsulated tumors originating from Schwann cells of peripheral nerves. In the head and neck region, they commonly arise from cranial nerves; however, sinonasal schwannomas are rare due to sparse innervation.

They most frequently originate from:

•              Branches of the trigeminal nerve (V1, V2)

•              Autonomic nerve fibers

Their nonspecific presentation often mimics:

•              Nasal polyps

•              Inverted papilloma

•              Malignancy

Thus, radiological and histopathological confirmation is essential.

Patient Details

•              Age/Sex: 49-year-old male

•              Presenting complaints:

o             Progressive unilateral nasal obstruction (right side)

o             Occasional nasal discharge

o             No epistaxis or visual symptoms

Radiological Findings

CT PNS (Axial & Coronal)

Key Findings:

•              Polypoidal soft tissue density mass in:

o             Right posterior ethmoid sinus

o             Sphenoid sinus

•              Mild heterogeneous enhancement

•              No significant bone destruction

•              No intracranial or orbital extension

👉 Suggestive of benign expansile lesion

Intraoperative Findings

•              Polypoidal, lobulated mass

•              Moderately vascular

•              Origin: posterior ethmoid region extending to sphenoid

•              Complete excision done endoscopically

•              Minimal intraoperative bleeding

Histopathological Findings

Gross

•              Multiple soft tissue fragments

•              Largest ~3 × 1.5 × 1 cm

Microscopy

•              Biphasic pattern:

o             Antoni A areas: hypercellular with nuclear palisading

o             Antoni B areas: hypocellular myxoid regions

•              Spindle-shaped cells with wavy nuclei

•              No atypia or malignancy

Diagnosis

✅ Schwannoma

Sinonasal schwannomas are rare and account for a very small fraction of sinonasal tumors.

Origin

Likely from:

•              Posterior ethmoidal nerve (branch of V1)

•              Sphenopalatine ganglion fibers

Clinical Features

•              Unilateral nasal obstruction (most common)

•              Rhinorrhea

•              Headache

•              Rarely epistaxis

Radiological Features

•              Well-defined soft tissue mass

•              Mild to moderate enhancement

•              Bone remodeling rather than destruction

👉 Helps differentiate from malignancy

Differential Diagnosis

•              Antrochoanal polyp

•              Inverted papilloma

•              Fungal sinusitis

•              Esthesioneuroblastoma

•              Sinonasal carcinoma

Histological Hallmarks

•              Antoni A & B areas

•              Verocay bodies (occasionally)

•              S-100 positivity (if IHC done)

Treatment

•              Endoscopic complete excision (gold standard)

•              No role of radiotherapy in benign lesions

Prognosis

•              Excellent

•              Recurrence rare if completely excised

•              Malignant transformation extremely rare

Sinonasal schwannoma should be considered in unilateral sinonasal masses, especially when imaging shows a well-defined lesion without aggressive bone destruction. Endoscopic excision provides excellent outcomes with minimal morbidity.

1.      Thompson LD. Sinonasal schwannoma. Head Neck Pathol.

2.      Shugar JM et al. Schwannoma of nasal cavity. Laryngoscope.

3.      Perzin KH, Panyu H. Non-epithelial tumors of nasal cavity.

4.      Friedman I et al. Tumors of nasal cavity and sinuses.

5.      Barnes L. Surgical pathology of head and neck tumors.