Other / Other / MRI

Sphenochoanal polyp

A patient with unilateral nasal obstruction, postnasal discharge, headache, or visual changes presents for imaging to evaluate a suspected choanal polyp and determine its sinus of origin prior to endoscopic surgery.

Key Images

Image 3

Image

Image 2

Look For First
  • Opacified sphenoid sinus with clear maxillary sinus—this asymmetry is the most reliable imaging clue that differentiates sphenochoanal from antrochoanal polyp
  • Unilateral soft-tissue mass extending from the sphenoid ostium through the sphenoethmoid recess toward the nasopharynx/choana
  • Stalk or pedicle originating within the sphenoid sinus and passing medial to the middle turbinate (away from the middle meatus)
Key Image Findings
  • On CT: The polyp appears as a unilateral, low-attenuation soft-tissue mass arising from the sphenoid sinus with an opacified (fluid-filled) sphenoid sinus and a clear, well-aerated maxillary sinus.
  • Expansion of the sphenoid ostium without bony erosion or cortical destruction is typical and supports benign inflammatory origin rather than malignancy.
  • The stalk or pedicle can be traced from the sphenoidal origin through the sphenoethmoid recess and into the nasopharynx/choana, confirming sphenoidal origin.
  • The polyp passes between the nasal septum and middle turbinate, keeping the middle meatus clear—a crucial distinction from antrochoanal polyp, which emerges through the middle meatus.
  • MRI shows T2 hyperintensity within the mass and T2 hyperintensity/fluid signal in the opacified sphenoid sinus, reflecting inflammatory/cystic contents.
  • On MRI, the stalk demonstrates clear continuity with the sphenoid sinus mucosa, establishing site of origin definitively.
Differential Diagnosis
  • Antrochoanal polyp (ACP): Arises from the maxillary antrum with an opacified maxillary sinus; stalk emerges through the middle meatus rather than passing medial to the middle turbinate; maxillary and sphenoid sinuses are clear.
  • Ethmochoanal polyp: Originates within the ethmoid sinus; typically bilateral or midline presentation; ethmoidal origin can be traced on imaging.
  • Inverted papilloma: May present as a unilateral sinonasal mass; typically shows mixed signal intensity, bone erosion or hyperostosis, and irregular margins; requires histologic confirmation.
  • Pituitary adenoma: Can extend into the sphenoid sinus; usually arises from within the sella turcica rather than polypoidal from the sinus mucosa; MRI shows connection to the sella and pituitary gland.
  • Squamous cell carcinoma or adenocarcinoma: More common in older patients; shows aggressive features (bone erosion, heterogeneous enhancement, cervical lymphadenopathy) and requires biopsy.
  • Lymphoma: May present as a sphenoidal mass; typically shows homogeneous enhancement and often presents with systemic symptoms; requires biopsy for diagnosis.
Discussion

Sphenochoanal polyp is a rare, benign, solitary inflammatory polyp representing a small minority of all choanal polyps (~4–6% of all nasal polyps); it is far less common than antrochoanal polyp.

Histologically, sphenochoanal and antrochoanal polyps are indistinguishable, making imaging identification of the sinus of origin essential for diagnosis and surgical planning.

Endoscopy alone is insufficient for diagnosis: on anterior rhinoscopy, a sphenochoanal polyp appears identical to an antrochoanal polyp; only the endoscopic clue that it passes medial to the middle turbinate (leaving the middle meatus clear) hints at sphenoidal origin.

CT and/or MRI are mandatory to establish the site of origin and plan appropriate endoscopic surgery, which requires complete removal of both the choanal component and the sphenoidal source.

Any mass arising from the sphenoid sinus must raise suspicion for neoplasm: in one case series, 3 of 6 isolated sphenochoanal masses were tumors (2 inverted papillomas, 1 pituitary adenoma), underscoring the importance of histologic confirmation.

Incomplete polypectomy that leaves sphenoidal tissue behind carries a high recurrence risk; endoscopic removal with widening of the sphenoid ostium and complete eradication of sphenoidal origin is the treatment of choice.

Reporting Pearls

Clearly identify the sinus of origin on imaging by tracing the stalk back into the sphenoid sinus and documenting the "opacified sphenoid, clear maxillary sinus" pattern; explicitly state that the polyp passes medial to the middle turbinate (not through the middle meatus) and describe the sphenoid ostium widening, confirming sphenoidal origin and guiding the surgeon to the correct sinus for complete removal.

Pitfalls
  • Mistaking a sphenochoanal polyp for an antrochoanal polyp on endoscopy alone, leading to incomplete surgical planning; always correlate with imaging to confirm site of origin.
  • Overlooking the opacified sphenoid sinus on imaging and focusing only on the choanal component, thereby failing to identify the sphenoidal origin and risking incomplete removal.
  • Failing to raise suspicion for malignancy when encountering any mass in the sphenoid sinus; up to 50% of isolated sphenochoanal masses may be neoplastic, requiring tissue diagnosis and careful evaluation for signs of erosion or aggressive features.
  • Incomplete surgical removal that leaves sphenoidal tissue behind, which carries a high recurrence risk; the surgeon must remove the entire sphenoidal source and widen the sphenoid ostium.
Source: Reference source

Secondary Links

HomeSinusesAnatomyGeneral Resources