Histology and histochemistry of nasal polypsShaila A Nimbkar, Sudha Y Sane
Department of Pathology, Seth G.S. Medical College and K.E.M. Hospital, Parel, Bombay-400 012, India
Surgically removed nasal polyps have been studied histologically and histochemically. Out of the 70 specimens studied, 55 polyps (77.2%) were of edematous type with allergy and infection as the etiological factors while 15 (22.8%) constituted rest of the types which are not likely to be allergic in nature. The standard line of treatment of nasal polyps is combined anti-allergic and anti-inflammatory, but for the polyps which are not allergic in nature, we propose that mere surgical resection without antiallergic therapy would suffice for the complete cure.
Nasal polyp is a routine out patient problem. Though it is a common condition the exact structure and etiology is debatable. Virchow and his pupils  believed polyp to be myxomatous tumour. Eggston and Wolff  view it as passive edema of mucosa. Anderson and Bing' have shown it as proteinaceous exudate, while Weisskopf and Burn  consider that it has acid mucopolysaccharides. The present work was undertaken to reassess the histological and histochemical features of nasal polyps, which may help to understand the nature and plan the treatment.
Two hundred and fifty tumours and and tumour-like lesions obstructing nasal passage were received at the Surgical Pathology Department during two years. Out of these 70 (27%) were nasal polyps with a pedicle attached in nose or paranasal sinuses.
Gross appearance of the polyps was noted down. Two to three sections were taken from each polyp including the stalk. Paraffin sections were prepared. Apart from routine staining with haematoxylin and eosin the following stains were used wherever indicated.
Histologically polyps were studied with special reference to the changes in the mucosa and in the basement membrane, type of inflammatory cells, glands, vessels and stroma.
The size of the polyp varied from about 1 cm. to 10 cm. They were oval or pear shaped with a pedicle. Covering mucosa was smooth, translucent or opaque and partly ulcerated. Cut surface of most of the polyps showed grey semitranslucent, edematous, jelly like material. A few specimens showed areas of congestion and haemorrhage while some others showed cystic changes.
The polyps were histologically typed into five groups as shown in [Table 1].
See [Figure 1] on page 230B
This is the commonest type of polyp. Fifty four out of seventy were of this group. The main feature of the polyp was severe edema of tunica propria. The covering epithelium varied from normal respiratory mucosa to partial or complete denudation. Squamous metaplasia was seen in 8 polyps, while 5 showed papillary hyperplasia of the epithelium. The basement membrane was thickened in 31 polyps. It was PAS positive. The ciliated columnar epithelium showed PAS positive material in the cells. It was diastase resistant and was positive with Alcian blue and mucicarmine, indicating the presence of acid mucopolysaccharides and mucoprotein, but no glycogen. In areas of squamous metaplasia, the deepest layer was PAS negative, while PAS positivity appeared towards the surface.
Unlike normal respiratory epithelium, the surface epithelium of the polyp occasionally invaginated into the stroma and produced inclusion glands. The cells lining the glands were cilliated, columnar, cuboidal to flattened. The histochemical characters were similar to those of the surface epithelium. The PAS positiveness decreased as the cells became flattened.
The stroma consisted of reticular network, ground substance with inflammatory cells and vessels. The ground substance was negative with PAS and Alcian blue indicating the absence of carbohydrate and acid mucopolysaccharide. The organization of edematous polyp was accompanied by fibroblastic proliferation with formation of collagen and reticulin specially in subepithelial layer and around vessels and glands. This was well demonstrated by Elastic Van Gieson stain. It also showed PAS positivity due to collagen.
The inflammatory cells were predominent in the subepithelial layer and around vessels. They were mainly eosinophils, plasma cells, lymphocytes and mononuclear cells. Polymorphs were seen only in ulcerated areas. Toluidine blue stain showed significant number of mast cells in edematous polyps.
Ten per cent of the polyps were of fibrous type. The main core of these polyps was formed by collagenous connective tissue, demonstrated by Masson's trichrome and Van Gieson stains. Most of the surface was covered by stratified squamous epithelium. At places columnar epithelium was present without cilia, Inflammatory cell infiltration was scanty.
Glandular polyps See [Figure 2] on page 230B
Six polyps were of this variety. The invagination of the surface epithelium into the lamina propria produced gland like structures, which were seen in polyps of all varieties while glandular polyps were mainly formed by seromucinous glands. The mucous glands were distended with secretions. Extreme distension of glands formed degenerating cysts, which are classified as cystic polyps by Cameran.  The lining epithelium as well as secretions showed strong PAS positivity, resistant to diastase. The staining characters of invagination type glands were similar to those of surface epithelium; of normal nasal mucosa.
Four polyps were characterised by presence of many dilated capillary spaces lined by endothelium and filled with red blood cells suggesting angiomatous polyps. The inflammatory cells wept scanty in this type of polyps.
Congo red stain was done on four polyps which were suspected to have amyloid material on haematoxylin and eosin stain but these polyps were negative for amyloid.
The histological study reveals that the commonest variety of nasal polyps is oedematous which is shown to have allergic basis by many workers while other types which together form about one third of polyps have different etiology. We perceive our environment through our sensory receptors of nose. The mucosa of the ethmoid region is the most common target organ for the allergic reaction leading to the formation of polyp. The polyps also arise in the paranasal sinuses and pass via the osteum to the choana. Rarely the mucosal covering of the turbinates and septum show polyp formation. Eggston's  concept of the etiology of polyp is that it arises due to basic vascular changes in the nasal mucosa induced by repeated attacks of sinusitis, periphlebitis, obstruction of return flow of interstitial tissue fluid leading to passive congestion and edema. The pioneer work of Kern and Schenck  introduced the concept that the nasal polyp is allergic in origin. Berdal  states that accumulation of reagins and ample edema in polyp is due to allergic inflammation. Schenck  observed that during active nasal allergy there is degranulation of mast cells with release of histamine. This attracts eosinophils. Tandon et al  observed no difference in the histological appearance of allergic and infective polyps.. While Kaker  assessed the effect of cortisone therapy in nasal polyps and he found good response specially in small ethmoidal polyps with edematous mucosa.
In the present study, ground substance of nasal polyps was PAS negative and did not stain with alcian blue indicating that the stroma did not contain acid mucopolysacharide. This agrees with the findings of Taylor  while it is in direct contrast to Weisskopf and Burn  who observed the constant presence of acid mucopolysaccharides in all polypoid tissue indicating that the polyp is an active progressive growth of connective tissue, rather than due to mechanical engorgement of extravasated edema fluid.
The glandular polyps are mainly formed by the disease of the glands of respiratory mucosa. The ducts of the infected glands become obstructed. cystic and produce periglandular irritation with polyp formation.
Angiectatic polyps are comparatively rare. These usually present as pedunculated haemorrhagic masses arising from Little's area of the nasal septum. Hypertrophy of the nasal spur causes repeated trauma to the septal vessels. This leads to proliferation of septal vessel with exudation of plasma like fluid and formation of polyp.
We are grateful to Dr. C. K. Deshpande, M.D., F.R.C.P. Dean, Seth G.S. Medical College and K.E.M. Hospital, Bombay 400 012 for permitting us to publish the hospital material.
We are also grateful to Dr. (Mrs.) S. M. Sant, M.D. Head and Professor of Pathology, Seth G.S. Medical College, for allowing us to use the surgical Pathology material.
[Figure 1], [Figure 2]