Subcutaneous rhinosporidiosis masquerading as soft tissue tumor: diagnosed by fine-needle aspiration cytology.

Rhinosporidiosis is a chronic granulomatous lesion caused by Rhinosporidium seeberi. It frequently involves nasopharynx and ocular region. Presenting as cutaneous and subcutaneous mass is extremely rare. This report describes the FNA cytology of rhinosporidiosis occurring as a soft tissue mass in the right mid thigh region. We present a rare case of a 71-year-old male, who presented with multiple subcutaneous soft tissue mass lesions in the posteromedial aspect of mid right thigh region since 2 weeks. Local examination revealed multiple firm to hard mass with skin over the swelling was unremarkable. CT of the right thigh showed a heterogeneous lesion with infiltrative margins in the thigh. Clinically soft tissue sarcoma was considered. Diagnostic FNAC was performed showing numerous mature and immature sporangias with giant cell reaction. Hence, an excision biopsy confirmed the rhinosporidiosis. To conclude, the FNAC diagnosis of rhinosporidiosis is specific. Preoperative diagnosis is possible even in cases with unusual clinical presentations.

What was known?

The rhinosporidiosis with disseminated is very rare phenomenon. Very few literature supports for FNAC as diagnostic tool in such cases. In these reported cases, patients are known case of nasal or ocular rhinosporidiosis with dissemination detected by FNAC.

Introduction

Rhinosporidiosis is a chronic granulomatous lesion caused by Rhinosporidium seeberi.[123] Clinically, rhinosporidiosis presents as pedunculated polypoidal soft tissue mass. Nose and nasopharynx are the most common sites involved, accounting for more than 70% cases. Ocular lesions, particularly of the conjunctiva and lacrimal sac, account for 15% cases.[23] Rare sites of involvement are lips, palate, uvula, maxillary antrum, epiglottis, larynx, trachea, bronchus, ear, scalp, vulva, penis, rectum and skin. Rarely, disseminated infections are also reported involving limbs, trunk and viscera especially in the immunocompromised patients.[234] Presenting as cutaneous and subcutaneous mass is extremely rare.[34] We describe a case of FNA cytology experience of rhinosporidiosis occurring as a soft tissue mass in the right mid thigh region.

Case Report

A 71-year-old male presented with multiple subcutaneous soft tissue mass lesions in the postero medial aspect of mid right thigh region since 2 weeks. Local examination revealed multiple firm to hard mass with skin over the swelling being unremarkable [Figure 1a]. CT of the right thigh showed a heterogeneous lesion with infiltrative margins in the thigh. Clinically soft tissue sarcoma was considered. Routine hematological and biochemical investigations were unremarkable. HIV and HBs Ag tests were nonreactive. Diagnostic FNAC was performed showing numerous mature and immature sporangias with giant cell reaction [Figure 1c and d]. Intraoperatively, the mass was irregular and nodular grey white [Figure 1b]. An excision biopsy showed multiple grey white masses with cystic and mucoid areas [Figure 2a]. Histopathology confirmed the rhinosporidiosis with numerous mature and immature sporangia surrounded by dense inflammatory response [Figure 2b]. Complete ENT examination revealed no obvious rhinosporidial lesion. The patient is under regular follow up since 1 year without any evidence of recurrence.

Figure 1

(a) Clinical photograph showing nodular mass in subcutaneous plane in the thigh (b) Intraoperatively nodular grey white mass in the subcutaneous plane (c) Lesional aspiration showing many mature sporangia with endospores in background [Papanicolou stain, ×400] (d) Lesional aspiration showing many mature and immature sporangia [Papanicolou stain, ×400]

Figure 2

(a) Gross specimen showing multiple grey white masses with cystic and mucoid areas (b) Histopathology showing with hyperplastic epithelium and immature spornagias with giant cell reaction [H and E, ×400]

Discussion

Rhinosporidiosis is a rare disease, known for many years and first described in argentina.[13] The mode of infection from the natural aquatic habitat of R. seeberi is through the traumatized epithelium.[234] It is an aquatic protozoan and recent taxonomy suggests it is now a new eukaryotic group of protists known as Mesomycetozoa. Ahluwalia et al. suggested the cyanobacterium Microcystis aerogenosa as the causative agent which has been isolated from clinical samples as well as water samples in which patients are taking bath.[56] There is evidence for hematogeneous spread of rhinosporidiosis to anatomically distant sites especially in immunocompromised individuals.[2] However in our case, HIV was nonreactive and mode of dissemination to a distant site is obscure.

A typical polypoid appearance of the lesions often helps in correct preoperative diagnosis. However, atypical presentations may cause confusion with soft tissue tumors or papillomas.[245] Aspiration cytology can be helpful in these cases.[235] Microscopically, demonstration of endospores of 5-10 μm and sporangium of 50-1000 μm in the cytological smears clinches the diagnosis. Background shows granulomatous reaction. The endospores may be confused with epithelial cells. The PAS stain is used to discriminate between endospores and epithelial cells, in which the residual cytoplasm and large nuclei can sometime simulate the residual mucoid sporangial material around the endospores.[245] In our case, aspiration cytology was classical of rhinosporidiosis and hence PAS stain was not performed.

R. seeberi should be distinguished from Coccidioides immitis.[234] The latter has similar mature stages represented by large, thick-walled, spherical structures containing endospores, but the spherules are smaller (diameter of 20-80 μm versus 50-1000 μm) and contain small endospores (diameter of 2-4 μm).[134]

The definitive diagnosis of rhinosporidiosis is by histopathology on biopsied or resected tissues, with the demonstration of sporangia and endospores.[245] The sporangia are large, thick-walled spherical structures with endospores seen in a fibromyxomatous or fibrous stroma containing chronic inflammatory cells, which include macrophages and lymphocytes. Each mature sporangium contains an operculum or pore through which the endospores are extruded.[245] Our case also showed similar histopathological finding.

The only curative approach is the surgical excision combined with electro coagulation.[245] There is no demonstrated efficacy in using antifungal and/or antimicrobial drugs. Recurrence, dissemination and local secondary bacterial infections are the most frequent complications. Dapsone, ketconazole, ciprofloxacin and amphotericin have been tried with varied success.[345] Our case was managed with surgical excision and on 1 year of follow up no evidence of recurrence was noted.

Conclusion

The FNAC diagnosis of rhinosporidiosis is specific. It can be diagnosed cytologically from its morphological features similar to histopathology. Preoperative diagnosis is possible even in cases with unusual clinical presentations.

What is new?

The disseminated rhinosporidiosis without nasal or ocular lesion is very rare phenomenon and diagnosing such cases by FNAC is very challenging. Our case is of first of its kind in the literature