Sinonasal Myxoma: A Distinct Entity or a Myxoid Variant of Desmoid Fibromatosis?

Sinonasal Specific Bone Lesions, Including Fibro-Osseous and Select Odontogenic Lesions

Sinonasal bone lesions encompass a diverse spectrum, ranging from nonneoplastic and benign conditions to aggressive, malignant neoplasms. These lesions can affect individuals across various age groups, from pediatric to adult patients. Recognizing these entities is crucial, given the variability in treatment approaches, recurrence rates, and prognoses. This review explores the common and uncommon but distinctive bone lesions affecting the sinonasal region, highlighting key clinical, radiographic, morphologic, and genetic features for each. Additionally, we provide helpful tips on distinguishing and accurately classifying each lesion within its relevant differential diagnoses.

Sinonasal Myxoma in an Infant: Observations on Its Distinctiveness and a Discussion on Potential Reclassification As Infantile Intraosseous Myxoid Desmoid Fibromatosis

Myxomas, when they manifest in the paranasal sinuses and/or maxillae of infants, are classified as sinonasal myxomas (SNMs). We present a case of SNM in the maxilla of a 15-month-old infant. Following the initial surgical intervention, the patient unfortunately experienced a recurrence of the condition. However, a subsequent surgery employing marginal excision was performed, and since then, no further recurrence has been reported. SNM exhibits consistent clinical features and histological characteristics that are distinct from those of odontogenic myxomas. Furthermore, in this case, immunohistochemical staining was positive for β-catenin, whereas odontogenic myxomas are generally negative for β-catenin staining. Another study reported that SNMs share genetic mutations with desmoid tumors, which are not observed in odontogenic myxomas. This suggests that this entity is distinct from odontogenic myxomas, leading us to propose that it may indeed represent a separate disease entity. This fact may lead to the reclassification of the disease and, ultimately, to changes in treatment strategies.

Spindle Cell Tumors of the Sinonasal Tract: A Diagnostic Update with Focus on Ancillary Workup

Spindle cell neoplasms arising in the head and neck may be challenging to recognize due to their relative rarity. While underlying molecular alterations are increasingly elucidated, testing for these features may not be readily available. In most cases, combinations of key morphologic features and diagnostic immunohistochemical markers can be used to replace molecular diagnostics. Conversely, some molecular alterations and expression of their surrogate biomarkers are not specific for any one entity, and it is important to recognize these to avoid diagnostic pitfalls. In this review, we discuss both old and new spindle cell tumors of the sinonasal tract, with an emphasis on histologic features and clinically relevant immunohistochemical markers serving as surrogate markers for underlying genomic alterations.

CTNNB1 and APC Mutations in Sinonasal Myxoma : Expanding the Spectrum of Tumors Driven By WNT/β-catenin Pathway

Sinonasal myxoma (SNM) is a rare, benign mesenchymal neoplasm with distinct clinicopathologic features and aberrant nuclear localization of β-catenin by immunohistochemistry. The molecular underpinnings have been linked to that of a "myxoid variant" of desmoid fibromatosis. Herein, we describe a series of 8 cases of SNM and propose clinical and biologic differences compared with desmoid fibromatosis. Our patient cohort is comprised of 5 males and 3 females (age range: 10 mo to 12 y), 6 of whom are aged less than or equal to 24 months. All presented with facial swelling, reflecting lesions involving the maxillary bone, and all underwent resection. All tumors were variably cellular and comprised of bland spindled to stellate cells in a profusely myxoid background with diffuse nuclear β-catenin expression. All cases of SNM were analyzed by next-generation sequencing using the Oncopanel assay. Three cases failed sequencing, 2 of 5 successful cases exhibited exon 3 CTNNB1 alterations involving the ubiquitin recognition motif, and 3 had adenomatous polyposis coli ( APC ) deletions. One patient had APC germline testing which was negative. No germline testing was available for the remaining 7 patients. Follow-up data over a range of 1 month to 23 years was available for 7 of the 8 SNMs. One case patient had local recurrence, and all were alive without evidence of disease. This is in contrast to the high recurrence rate typically seen in desmoid fibromatosis, particularly after resection. Our findings expand the spectrum of tumors with underlying WNT/β-catenin pathway and highlight the histologic, clinical, and genetic differences of SNM compared with desmoid fibromatosis. APC deletion raises the possibility of underlying germline alteration and familial adenomatous polyposis.

Infantile Sinonasal Myxoma Is Clinically and Genetically Distinct From Other Myxomas of the Craniofacial Bones and From Desmoid Fibromatosis

Sinonasal myxomas are rare benign tumors of the maxillary bone and sinus. There is published evidence that sinonasal myxomas occurring in children up to 3 years of age ("infantile sinonasal myxomas") are clinically distinctive and harbor Wnt signaling pathway alterations. Here, we characterized 16 infantile sinonasal myxomas and compared them to 19 maxillary myxomas and 11 mandibular myxomas in older patients. Clinical follow-up was available for 21 patients (46%) overall (median: 2.6 y; range: 4 mo to 21 y), including 10 of 16 infantile sinonasal myxomas (62%). None of the 8 resected infantile sinonasal myxomas recurred, despite positive margins in 6 of them. One incompletely resected infantile sinonasal myxoma underwent partial regression without additional treatment. In contrast, 4 of the 11 other myxomas with follow-up recurred (36%), including one that recurred twice. Imaging studies demonstrated all infantile sinonasal myxomas to be expansile lesions arising from the anterior maxillary bone adjacent to the nasal aperture, with peripheral reactive bone formation. Histologically, infantile sinonasal myxomas showed short, intersecting fascicles of bland fibroblastic cells with prominent stromal vessels. Examples with collagenous stroma showed some morphologic overlap with desmoid fibromatosis, although none showed infiltrative growth into adjacent soft tissue. Immunohistochemistry demonstrated nuclear β-catenin expression in 14 of 15 infantile sinonasal myxomas (93%), in contrast to 4 of 26 other myxomas of craniofacial bones (15%). Smooth muscle actin was expressed in only 1 of 11 infantile sinonasal myxomas (9%). Next-generation sequencing was successfully performed on 10 infantile sinonasal myxomas and 7 other myxomas. Infantile sinonasal myxomas harbored CTNNB1 point mutations in 4 cases (D32Y, G34E, G34R, and I35S), and none harbored alterations to the phosphorylation sites T41 and S45 that are altered in 99% of CTNNB1 -mutant desmoid fibromatoses. Three tumors showed alterations consistent with biallelic APC inactivation. Three infantile sinonasal myxomas that showed strong nuclear β-catenin expression were negative for CTNNB1 and APC alterations. Sequencing was negative for CTNNB1 or APC alterations in all 7 myxomas of craniofacial bones in older patients. Four of these myxomas in older patients (57%) showed copy number alterations, and all lacked known driving alterations. These findings support the notion that infantile sinonasal myxomas are clinically and genetically distinctive, and we propose the use of the diagnostic term "infantile sinonasal myxoma" to distinguish this tumor type from other myxomas of the craniofacial bones. Infantile sinonasal myxoma should be distinguished from desmoid fibromatosis because of its unique clinical presentation, more indolent clinical behavior, different morphology, different immunohistochemical profile, and different genetics. Given its indolent behavior even when marginally excised, infantile sinonasal myxoma can be managed with conservative surgery.