Inverted papilloma (Schneiderian papilloma — inverted type) is a benign but locally aggressive neoplasm arising from the Schneiderian membrane of the sinonasal mucosa. It accounts for approximately 0.5-4% of all sinonasal tumors and most commonly originates from the lateral nasal wall, particularly the middle meatus and ethmoid infundibulum region. Histopathologically, it demonstrates an endophytic (inward) growth pattern with epithelial hyperplasia growing into the underlying stroma — this inverted growth pattern gives the lesion its name. Association with HPV types 6, 11, 16, and 18 has been reported, with higher malignant transformation risk in HPV 16/18 positive cases. The rate of malignant transformation (squamous cell carcinoma — SCC) is reported between 5-15%, and this risk is the fundamental reason the lesion requires aggressive surgical treatment. The pathognomonic 'cerebriform' (brain gyri-like) enhancement pattern on MRI strongly supports the diagnosis. Postoperative recurrence rate is 15-20%, requiring endoscopic follow-up for 5 years.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Inverted papilloma develops through neoplastic proliferation of the Schneiderian membrane (ectodermal-origin sinonasal respiratory epithelium); the normal surface epithelium grows in an inverted fashion into the stroma, forming thick, interdigitating epithelial plications. This endophytic growth pattern translates to cerebriform enhancement on MRI: the stromal vascular cores between the epithelial infoldings enhance while the avascular epithelial layers do not — these alternating enhancing and non-enhancing bands create an appearance resembling brain gyri (gyrus-sulcus pattern). The tumor's lateral nasal wall origin is attributed to the Schneiderian membrane being embryologically thicker and more glandularly rich in this region. As the tumor grows, it produces pressure-related remodeling and focal erosion of surrounding bony structures; however, extensive bone destruction suggests malignant transformation. Malignant transformation (SCC) typically begins in the deep stromal component of the tumor and is associated with p53 mutation, cyclin D1 overexpression, and HPV E6/E7 oncoprotein activation — these molecular changes lead to loss of cell cycle control and invasive growth.
The cerebriform (brain gyri-like) enhancement pattern seen as alternating enhancing stromal bands and non-enhancing epithelial bands on contrast-enhanced MRI is considered pathognomonic for inverted papilloma. The presence of this pattern distinguishes inverted papilloma from other sinonasal lesions with over 90% sensitivity and over 95% specificity. Loss of the pattern or conversion to solid homogeneous enhancement should be alerting for malignant transformation (SCC).
On contrast-enhanced T1-weighted sequences, inverted papilloma demonstrates the pathognomonic 'cerebriform' enhancement pattern. This pattern appears as alternating enhancing stromal bands and non-enhancing epithelial bands within the tumor, creating a convolutional appearance resembling brain gyrus-sulcus structure. The enhancing stromal bands correspond to vascular-rich fibrous cores, while the non-enhancing bands correspond to avascular thick epithelial layers. This pattern is most prominently seen as regular parallel striations from periphery to center, best visualized on coronal and sagittal planes. While the cerebriform pattern reflects the benign inverted papilloma nature of the tumor, loss of this pattern or replacement with solid homogeneous enhancement suggests malignant transformation.
Report Sentence
On contrast-enhanced T1-weighted sequences, the lesion demonstrates pathognomonic cerebriform enhancement pattern (alternating enhancing and non-enhancing bands), findings consistent with inverted papilloma.
On T2-weighted sequences, inverted papilloma shows intermediate signal intensity — neither markedly hyperintense as in polyposis nor hypointense as in desiccated secretions. A convoluted striation pattern similar to the cerebriform pattern on contrast-enhanced sequences may also be seen on T2. Epithelial layers show slightly hyperintense T2 signal while stromal bands show slightly hypointense signal — although this signal difference is not as pronounced as on contrast-enhanced sequences, it provides diagnostic clues. Peritumoral obstructed sinus secretions show variable signal on T2. The intermediate T2 signal of the tumor reflects the difference of its solid structure from edema-dominant polypoid tissue and is a critical finding in differential diagnosis.
Report Sentence
On T2-weighted sequences, the lesion demonstrates intermediate signal intensity with discernible convoluted striation pattern within the lesion.
On non-contrast CT, focal hyperostosis or sclerosis is seen at the attachment point of the inverted papilloma to the bone wall. This finding indicates the origin point of the tumor and is critically important in endoscopic surgical planning because drilling of the bone where the tumor root is located is required for complete excision. The attachment point is most commonly seen on the lateral nasal wall (anterior end of middle turbinate, ethmoid infundibulum, uncinate process area). The hyperostosis reflects new bone formation due to chronic tumoral irritation and periosteal reaction. This focal sclerosis pattern is not seen in polyposis and most other benign lesions and is a highly specific CT finding for inverted papilloma.
Report Sentence
Focal bone hyperostosis/sclerosis is noted at the lateral nasal wall/middle turbinate level corresponding to the tumor attachment point, indicating the origin point of the inverted papilloma.
On contrast-enhanced CT, inverted papilloma demonstrates heterogeneous solid enhancement. Enhancement is generally moderate and inhomogeneous — enhancing solid areas are mixed with non-enhancing areas within the tumor. This heterogeneity is due to the different vascularity of stromal and epithelial components within the tumor. The spatial resolution of CT is insufficient to demonstrate the details of the cerebriform pattern seen on MRI; however, the presence of solid enhancement is helpful in differentiating from inflammatory polyps that show minimal or no enhancement. Peritumoral mucosal thickening and obstructed sinus secretions can complicate enhancement assessment.
Report Sentence
On contrast-enhanced CT, the lesion demonstrates heterogeneous moderate solid enhancement with significantly increased enhancement compared to inflammatory polyps.
On DWI, inverted papilloma may show mild to moderate diffusion restriction. ADC values are generally between 1.0-1.4 × 10⁻³ mm²/s, higher than ADC values of malignant tumors (typically <1.0 × 10⁻³ mm²/s) and lower than ADC values of simple polyps (>1.5 × 10⁻³ mm²/s). These intermediate ADC values reflect the moderate cellularity of inverted papilloma. Although DWI findings alone are not specific, they narrow the differential diagnosis when evaluated together with contrast-enhanced MRI findings. When malignant transformation develops (SCC), diffusion restriction becomes pronounced and ADC values decrease — therefore, a decrease in ADC values during follow-up should be alerting for malignancy.
Report Sentence
Mild diffusion restriction is noted in the lesion on DWI with intermediate ADC values (approximately ... × 10⁻³ mm²/s).
CT demonstrates a solid soft tissue mass filling the unilateral nasal cavity, originating from the lateral nasal wall. The mass typically begins at the middle meatus level and may extend to the ethmoid and maxillary sinuses. Smooth-margined pressure-related remodeling and thinning of surrounding bony structures is seen — uncinate process, middle turbinate, lamina papyracea, and medial wall of the maxillary sinus. In advanced cases, focal bone erosion may be seen but the absence of aggressive permeative destruction supports the benign character. The mass causes obstructive secretion accumulation in ipsilateral sinuses, producing sinus opacification. Determining the extent of the tumor and its relationship with adjacent structures on CT is fundamental for preoperative planning.
Report Sentence
A solid mass of soft tissue density filling the left/right nasal cavity and originating from the lateral nasal wall is identified, with smooth-margined pressure remodeling of surrounding bony structures; no aggressive bone destruction is identified.
On endoscopic ultrasonography, inverted papilloma appears as a solid hypoechoic mass showing a more heterogeneous echopattern compared to inflammatory polyps on B-mode ultrasound. Color Doppler examination demonstrates significant vascular flow within the tumor — this feature is a critical finding in differentiating from avascular/hypovascular inflammatory polyps. The vascular signal corresponds to the fibrovascular cores in the tumor stroma and correlates with stromal enhancement on contrast-enhanced MRI. Power Doppler is more sensitive than color Doppler at low flow velocities and provides an advantage in demonstrating small tumor vessels. However, ultrasonography is limited in evaluating the deep extent of the tumor and bone relationship and cannot replace CT/MRI.
Report Sentence
On endoscopic ultrasonography, a solid hypoechoic mass is noted with significant vascular flow signals within the lesion on color Doppler examination.
Criteria
Most common form (80-90%). Originates from the lateral nasal wall, particularly the middle meatus/ethmoid infundibulum region. Usually extends to ethmoid and maxillary sinuses.
Distinct Features
Focal hyperostosis on the lateral nasal wall (attachment point) and unilateral middle meatus-ethmoid mass on CT. Cerebriform enhancement pattern on MRI. Krouse staging system is used for extent assessment.
Criteria
Less common (10-15%). Originates from the medial or posterior wall of the maxillary sinus. Expands within the sinus causing remodeling of sinus walls.
Distinct Features
Focal hyperostosis on the maxillary sinus wall on CT, solid mass filling the sinus. May extend to the nasal cavity through the ostium (unlike antrochoanal polyp, solid, enhancing, and not showing three-component structure). Medial maxillectomy may be required.
Criteria
SCC development in 5-15% of cases. Can be synchronous (SCC at diagnosis) or metachronous (SCC during follow-up). Aggressive bone destruction, loss of cerebriform pattern, and marked diffusion restriction are warning findings.
Distinct Features
Replacement of cerebriform pattern with solid homogeneous enhancement, decrease in ADC values (<0.8 × 10⁻³ mm²/s), transformation of bone destruction from remodeling to aggressive permeative pattern, peritumoral dural enhancement or orbital invasion. Risk is increased in HPV 16/18 positive cases.
Distinguishing Feature
Sinonasal polyposis is bilateral and multiple, shows markedly hyperintense signal on T2 (different from the intermediate T2 signal of inverted papilloma), demonstrates minimal peripheral enhancement on contrast-enhanced sequences (no cerebriform pattern), and no bone hyperostosis is seen.
Distinguishing Feature
SCC shows marked aggressive bone destruction (irregular, permeative pattern), pronounced diffusion restriction on DWI (ADC <0.8 × 10⁻³ mm²/s), and homogeneous solid enhancement — no cerebriform pattern. Perineural spread and deep tissue invasion are characteristic features of SCC.
Distinguishing Feature
Antrochoanal polyp is predominantly cystic (markedly hyperintense on T2, hypointense on T1), shows minimal/no enhancement, and exhibits three-component structure (cyst + pedicle + polyp). Inverted papilloma is a solid mass with intermediate T2 signal and significant enhancement.
Distinguishing Feature
JNA occurs in adolescent males, shows intense homogeneous enhancement on CT, pterygopalatine fossa widening is characteristic, and prominent 'flow void' signals are seen on MRI. Inverted papilloma shows heterogeneous enhancement, does not involve the pterygopalatine fossa, and does not show flow voids. Angiography before biopsy is mandatory in JNA — serious bleeding risk.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
Cerrahi sonrası ilk 2 yıl her 6 ayda bir, ardından 3-5 yıl boyunca yıllık endoskopik kontrol ve MRG takibi. Rekürrens oranı %15-20 olup attachment point bölgesi dikkatle değerlendirilmelidir.Inverted papilloma is a benign neoplasm requiring surgical treatment due to malignant transformation risk (5-15% SCC). Standard treatment is complete excision via endoscopic medial maxillectomy or endoscopic modified Lothrop procedure with mandatory drilling of the bone at the attachment point. Preoperative CT is needed for bone anatomy and attachment point localization, while MRI is needed for tumor extent, cerebriform pattern confirmation, and exclusion of malignant transformation. Incomplete resection is the main cause of recurrence. Loss of cerebriform pattern or decrease in ADC values during follow-up is alerting for malignancy. Biopsy is needed for histopathological diagnosis confirmation and exclusion of malignant transformation.
Inverted papilloma requires wide excision (endoscopic medial maxillectomy). Recurrence rate is 0-20% (depending on surgical technique). 5-15% risk of synchronous or metachronous SCC development. Focal hyperostosis is critical for surgical planning — indicates tumor attachment point.