Rhinosporidiosis

Rhinosporidiosis is a slowly progressive, chronic granulomatous infection that produces strawberry-like vascular polyps which bleed easily. It most often affects the lining of the nose, the pharynx and the conjunctiva of the eye.

Historically it was grouped with the deep fungal infections because its sporangia look like those of fungi, but modern molecular studies (18S rRNA sequencing) have shown that the causative organism, Rhinosporidium seeberi, actually belongs to the Mesomycetozoea (the DRIP clade), aquatic single-celled organisms on the boundary between animals and fungi. At Haute-Derma, our management of rhinosporidiosis focuses on early recognition of its characteristic sporangial granulomas and on excising the polyp at its base with thorough electrocoagulation to reduce the high risk of recurrence.

Pathogenesis and Life Cycle

The Organism Rhinosporidium seeberi and Its Source

Rhinosporidium seeberi is an aquatic microorganism that has never been grown in vitro.
Source: stagnant fresh water, ponds, lakes, rivers and streams in tropical and subtropical regions.
Route of entry: through scratches or tiny breaks in the mucosa while bathing, swimming or washing the face in contaminated pond or lake water.

Developmental Cycle in Tissue

In human tissue, R. seeberi passes through stages that differ markedly in size:

Free spore (trophozoite / endospore): small (6–8 µm), single cells with a distinct nucleus.
Mature sporangium: the cell enlarges enormously into a giant sphere 100–350 µm across, visible to the naked eye as tiny white dots on the polyp surface.
Spore release: each sporangium holds thousands of endospores. When it ruptures through its pore, the endospores spill into the surrounding stroma and start a new cycle of infection, provoking a highly vascular granulomatous reaction.

Clinical Forms

Nasal and Nasopharyngeal Form (70%–80% of cases):

A soft, pink-red or pale gray polypoid growth, stalked or broad-based, with a bumpy surface dotted with countless tiny white or yellow spots (superficial sporangia just beneath the mucosa).
Symptoms: one-sided nasal blockage, blood-stained nasal discharge, a sensation of something in the nose and recurrent nosebleeds.

Ocular Form (15%–20% of cases):

Polyps arise on the palpebral or bulbar conjunctiva or in the lacrimal sac.
Symptoms: a gritty foreign-body sensation, constant tearing and a red, papilloma-like lump that bleeds easily with blinking.

Cutaneous and Other Extranasal Forms (Rare): secondary skin lesions from autoinoculation from nasal or ocular sores, appearing as warty nodules or verrucous plaques attached to the surrounding skin.

Clinical and Histologic Differential Diagnosis

Rhinosporidiosis	Ordinary Nasal Polyp	Squamous Cell Carcinoma of the Nasal Mucosa (SCC)
Red, strawberry-like papillary mass with tiny white dots	Translucent gray polyp with a smooth surface	Necrotic, ulcerated, invasive growth that bleeds easily
Bleeds very easily with light contact	Rarely bleeds spontaneously	Bleeds easily from necrotic areas
Giant sporangia (100–350 µm) packed with endospores	No sporangia; many eosinophils	Atypical epithelial cells with abnormal mitoses
Hyperplastic mucosa with numerous thick-walled sporangia in the stroma	Edematous connective tissue stroma with eosinophil infiltration	Malignant keratinocytes breaching the basement membrane
Cannot be cultured	No microorganism	No microorganism

Standard Diagnostic Workup at Haute-Derma

Surface Examination and Cytology:

Touch smear / aspiration: a cotton swab is gently wiped across the surface of the strawberry-like polyp, or a small tissue sample is crushed between two glass slides.
KOH / Giemsa wet mount: immediately reveals giant spherical sporangia (up to 300 µm across) containing thousands of round or disc-shaped endospores (6–9 µm across).

Mandatory Biopsy for Histopathology:

Epithelium/mucosa: edematous, irregularly hyperplastic, or thinned by pressure from the mass.
Stroma: a chronic inflammatory granulomatous reaction with marked vascular proliferation (which explains the tendency to bleed).
Characteristic organisms: numerous sporangia at different stages of development:
- Immature, thin-walled sporangia with a central nucleus.
- Mature sporangia with very thick walls, packed with endospores.
- Ruptured sporangia: collapsed walls surrounded by multinucleated giant cells and neutrophils.
Special stains: the spores and sporangial walls stain strongly with PAS (periodic acid–Schiff) and GMS (Grocott's methenamine silver).

Treatment at Haute-Derma

Surgical Excision With Electrocautery of the Polyp Base

Because Rhinosporidium seeberi cannot be cultured and responds very poorly to standard antifungal drugs, complete surgical removal is the mainstay of treatment:

Technique: the papillary polyp is excised in one piece.
Electrocautery of the base: the surgical base (the polyp's attachment) must be thoroughly cauterized to destroy sporangia lying deep in the submucosa. Removing the mass without cauterizing its base is the main reason recurrence rates can exceed 50%.

Adjuvant Medical Therapy to Prevent Recurrence

Dapsone:
- Mechanism: dapsone inhibits maturation of the sporangia and blocks folic acid synthesis in R. seeberi.
- Dose: 100 mg/day for 3–6 months after surgery.
- Indications: especially useful for extensive disease, when surgery cannot remove the entire base, or in patients with repeated recurrences.

Frequently Asked Questions (FAQs)

+Is rhinosporidiosis actually caused by a fungus or by a parasite?

For more than a century, Rhinosporidium seeberi was classed as a deep fungus because its sporangia and endospores look very much like those of Coccidioides immitis. Modern genetic analysis (18S rRNA sequencing), however, has placed R. seeberi in the Mesomycetozoea (the DRIP clade), a group of aquatic single-celled organisms that sit between animals and fungi. Although it is not a true fungus genetically, the disease is still managed by dermatology and ENT specialists.

+Why does rhinosporidiosis recur so often after surgery, and how can this be prevented?

The high recurrence rate has two main causes:

Small sporangia deep in the submucosa are not fully removed when the mass is excised.
Rough surgical handling ruptures mature sporangia, releasing thousands of endospores into the operative field and seeding infection into nearby healthy mucosa. Prevention: the surgeon should remove the mass whole without breaching it, cauterize deeply into the base of the polyp, and keep the patient on oral dapsone 100 mg/day for 3–6 months after surgery.

+Why does a rhinosporidiosis polyp look like a strawberry, and why does it bleed so easily?

The strawberry-like appearance comes from two factors together:

The countless tiny white or yellow dots on the surface are the tops of giant sporangia lying just beneath the mucosa.
The organism provokes an inflammatory reaction in the stroma with abundant granulation tissue and a very dense network of capillaries. This intense vascular growth beneath a thinned mucosa makes the mass very fragile, so even a light knock or blowing the nose can cause heavy bleeding.