Biphenotypic sinonasal sarcoma, initially named low-grade sinonasal sarcoma with neural and myogenic features, is a rare low-grade sarcoma of the nasal and paranasal sinuses. The tumor exhibits both neural and myogenic differentiation and thus can be problematic to diagnose histologically as elements can closely resemble other tumors (e.g. schwannoma, malignant peripheral nerve sheath tumors, various sarcomas) 1.
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Epidemiology
Biphenotypic sinonasal sarcomas tend to occur in middle-aged and older adults, with a predilection for females 2,3.
Clinical presentation
The clinical presentation is non-specific indistinguishable from other sinonasal masses. Patients typically present with nasal obstruction with or without facial pain 1. Eventually, local invasion of local structures (orbit, anterior cranial fossa) can also occur leading to additional signs and symptoms.
Pathology
Genetics
Biphenotypic sinonasal sarcomas are characterized by rearrangements of PAX3, a transcription factor responsible for skeletal muscle and neural crest differentiation 1. A number of genetic abnormalities have been identified in these tumors including PAX3-MAML3 fusion protein (t(2;4)(q35;q31.1) - most common; PAX3-NCOA1 fusion; PAX3-FOXO1 fusion; and as yet to be elucidated abnormalities referred to as PAX3-X 1,3.
Histology
These tumors are typically hypercellular, composed of uniform spindle cells 1,4.
Immunohistochemistry
Biphenotypic sinonasal sarcomas are usually positive for both S100 and smooth muscle actin (SMA) 1,4.
Radiographic features
Imaging features are non-specific with these tumor presenting as soft tissue masses usually of the nasal and/or ethmoidal air cells 4.
CT
CT is the modality of choice to assess the relationship of the tumor to the facial skeleton and base of skull. The tumors usually demonstrate hyperostosis of adjacent bone 4.
MRI
MRI demonstrates a sinonasal mass with the following signal intensities 4:
T1: hypointense to muscle
T1 C+: enhances
T2: hypointense to muscle
Treatment and prognosis
Unlike other sinonasal sarcomas, biphenotypic sinonasal sarcomas have a very low mortality 1-4. Although indolent, these tumors have a tendency to locally recur 1,2,4 and can eventually invade the orbit and base of skull. Distant metastases are not reported 2.
Differential diagnosis
The differential diagnosis of biphenotypic sinonasal sarcoma includes other masses of the nasal and paranasal sinuses, including 1,2,4:
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