Adult sino-nasal alveolar rhabdomyosarcoma

A 22-year-old male presented with recurrent episodes of epistaxis for 3 months, blurring of vision and diplopia for 2 weeks with swelling in the left side of neck 2 weeks ago. He underwent FNAC from the left neck lymph-node which was suspicious for malignancy.

The patient was referred for MRI and PET scan at our institute.

Contrast-enhanced MRI of the paranasal sinuses revealed a heterogeneously enhancing mass in the left sinonasal region which demonstrated hypointense signal on T1, hyperintense signal on T2 and showed diffusion restriction with central non-enhancing areas. It measured 5x3.8x3.7 cm (APxTRxCC). Medially, the mass was eroding the nasal septum to involve the right ethmoidal cells, laterally eroding the medial wall of the left maxillary sinus, nasal bone, medial orbital wall and extending to the orbit till the orbital apex abutting the optic nerve and extraocular muscles. Superiorly, it was extending till the posterior table of the frontal sinus, involving cribriform plate, olfactory groove, planum sphenoidale and indenting the frontal lobe of the brain with adjacent dural enhancement. Posteriorly, it was extending into the sphenoid sinus. Subsequently performed PET-CT demonstrated the mass to be FDG avid with bone erosions appreciated on CT images.

Soft tissue sarcomas are rare heterogeneous tumours of embryonic mesoderm origin predominantly affecting the pediatric population [1]. Only 1% to 2% of all adult head and neck malignancies are sarcomas [1]. Rhabdomyosarcomas(RMS) are common in children constituting 5% of cancers in childhood [2,3]. Subtypes include embryonal, alveolar, and pleomorphic types with the most common type being the embryonal type [3]. Alveolar Rhabdomyosarcoma (ARMS) is a rare primitive small round blue cell neoplasm and is usually seen in the 10-25 years age group with extremities being the most common site of involvement [3]. They are usually misdiagnosed, largely in adult population, since squamous cell carcinoma is the most common malignancy in the adult patients involving the sinonasal tract and limited immuno-phenotypic panel are usually being selected to confirm poorly differentiated carcinoma as the tissue samples are usually scanty for definitive diagnosis in most cases [2]. Differential diagnosis of small blue round cells of sinonasal tract is vast with overlapping clinical as well as imaging features [2]. Alveolar rhabdomyosarcoma shows skeletal muscle differentiation and histology displaying small blue round cell appearance, which may lead to wrong diagnosis [2].  MRI is the preferred imaging modality of choice; however, CT is complementary because bone involvement is better appreciated on CT. MRI shows low signal intensity on T1-weighted sequence and high signal intensity on T2-weighted sequences. Heterogeneity and necrosis may be seen in the alveolar subtype of Rhabdomyosarcoma and lymphadenopathy is common [3]. PET-CT has a role in differentiating tumour recurrence from post-therapeutic tissue changes [4]. RMS can be sub-divided into orbital, non-orbital-parameningeal, and non-orbital non-parameningeal. Central nervous system dissemination is common in parameningeal type and is often unresectable at the time of diagnosis [1].  Distant metastasis is seen usually in the lungs, liver and bones [1, 2, 3].

Immunohistochemistry (IHC) panel and genetic studies are usually confirmatory. Chromosomal translocations involving the FOXO1 gene in 80% of the cases [5].

Treatment option is usually surgery if excision is possible, which is followed by radiotherapy and chemotherapy [1, 2, 3]. 

The sinonasal mass in our study was consistent with the imaging findings, and FOX01 gene rearrangement was detected in 72% of the cells.

Patient consent: written informed consent was obtained from the patient.