Lars-Eric Stenfors

Anatomy of the Rat Middle Ear

The rat is of value in otological research for many reasons. For instance, the middle ear structures are easily approachable. Recently a couple of studies in the rat have been published concerning the

Repair of Experimental Tympanic Membrane Perforations

In this investigation the healing pattern of experimental central and marginal pars tensa perforations in cats and rats was studied by using light and scanning electronmicroscopic techniques. The perforations were closed by hyperplastic squamous epithelium exhibiting a marked keratin production. This keratin formed a membranous structure which primarily appeared to close the perforation. No ingrowth of squamous epithelium into the middle ear cavity could be detected. Generally speaking, the perforations had closed within 9-11 days in rats and within 12-14 days in cats.

Absorbable Gelatin Sponge (Gelfoam) In Otosurgery: One Cause of Undesirable Postoperative Results?: An Experimental Study in the Rat

Absorbable gelatin sponge (Gelfoam)--commonly used in otosurgery--was gently inserted or firmly packed into the middle ear cavities of rats. The postoperative changes were evaluated 2 to 3 months later when, apart from some air-filled canals leading from the tympanal orifice of the Eustachian tube towards the attic, the middle ear cavity had become filled with newly formed bone and an amorphous mass of adhesions and bridles. The mass consisted of loose connective tissue, with fibroblasts, vessels and inflammatory cells. The tympanic membrane was retracted and fixed to the promontory. There were no signs that any Gelfoam had been removed through the Eustachian tube. The authors proposed that similar tissue reactions may occur in tympano-plasties.

The Release of Histamine from the Pars Flaccida Mast Cells One Cause of Otitis Media with Effusion

In this experimental study in the rat, compound 48/80--a potent degranulating drug of mast cells--was instilled in the external auditory meatus towards the tympanic membrane. Moreover, effusion material was produced in the attic space by blocking the tympanic isthmus with a piece of Gelfoam applied through the tympanic bulla. Both these procedures caused a degranulation of the pars flaccida mast cells and subsequently histamine was detected in the rinsing fluid collected from the middle ear cavity. A possible direct cause of the effusion material in the middle ear cavity may be a degranulation of the pars flaccida mast cells, thus resembling an allergic reaction Type I.

Myringotomy Made by CO2 Laser An Alternative to the Ventilation Tube?:An Experimental Study

In order to examine whether a myringotomy made with a CO2-laser might be alternative to a ventilation tube, a perforation was made in the upper rear quadrant bilaterally, of 22 rats. The laser-made perforations showed a delayed healing pattern, about twice the closing time of a similar-sized perforation made with a myringotomy lancet. Serous effusion was constantly observed in the attic space during the first 9 days but only in one ear was there actual discharge through the perforation. The size of the perforation started to diminish when the hyperplastic keratinizing squamous epithelium reached the perforation border.

Mast cells in the pars flaccida of the tympanic membrane. A quantitative morphological and biochemical study in the rat

The present study has shown that the pars flaccida of the tympanic membrane of the rat is extremely rich in mast cells. The findings were compared with those from earlier investigations in the rat; the pars flaccida is one of the tissues in this animal in wich mast cells are most abundant.

Secretory IgA-, IgG- and C3b-coated Bacteria in the Nasopharynx of Otitis-Prone and Non-Otitis-Prone Children

The proportions of secretory IgA (SIgA)-, IgG- and C3b-coated bacteria obtained from a well-defined area on the posterior wall of the nasopharynx (NPH) close to the Eustachian tube were determined. Samples taken from 25 otitis-prone (OP) and 25 non-otitis-prone (NOP) children with normal serum levels of IgA and IgG were evaluated using an immunofluorescence assay. Both groups harboured significantly more nasopharyngeal bacteria coated with IgG than with SIgA (p < 0.001). The OP children had significantly fewer SIgA-coated bacteria (p < 0.05) but more C3b-coated bacteria (p < 0.01) in the NPH than the NOP children had. No significant difference was noted between the two groups regarding IgG coating. The occurrence of Branhamella catarrhalis in the NHP was more pronounced in the OP group (p < 0.05). No significant differences in the occurrence of other middle ear pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus) or quantitative dominance of pathogens were noted between the two groups. Deficiency in SIgA coating of the nasopharyngeal bacteria may contribute to the otitis-prone condition.

Structure and Healing Capacity of the Rat Tympanic Membrane After Eustachian Tube Occlusion

Obstruction of the Eustachian tube in rats results in an accumulation of serous fluid in the middle ear cavity. the fluid was first detected in the attic, and subsequently the whole cavity became filled. However, when a perforation of the tympanic membrane was performed in connection with experimental tube obstruction, the mesotympanon was found free from fluid, but not the attic, as long as the perforation remained open. After 9-11 days of obstruction the pars flaccida was found to be maximally retracted, forming a non-adhesive clean retraction pocket. in addition, marked ultrastructural changes were found to have taken place in the pars flaccida following tube obstruction. Finally, in spite of the occluded Eustachian tube, traumatic tensa perforation was found to heal rapidly.

The Role of the Pars Flaccida in the Mechanics of the Middle Ear

The role played by the pars flaccida in the functioning of the middle ear is not altogether clear. The aim of our research was to study the movements of pars flaccida in altering the air volume in the middle ear. By using a sond placed either in the tympanic bulla or in the Eustachian tube in the rat, the middle ear can be insufflated or aspirated with exact volumes of air. Pars flaccida reacted promptly to the changes, while pars tensa remained immobile. A large air volume caused perforation of the pars flaccida. It seems that pars flaccidas function may consist in maintaining a constant middle ear pressure within certain limits, by changing its position.

Middle Ear Effusion Caused by Mechanical Stimulation of the External Auditory Canal: An Experimental Study in the Rat

Mechanical stimulation of the external auditory canal (EAC) in rat, either by scratching or exposure to a stream of air, caused effusion behind an intact ear-drum both in the experimental ear and in the contralateral one. Histologically the pars flaccida appeared oedematous, especially its lamina propria; and was infiltrated by inflammatory cells indicating a vascular leakage. Determination of the histamine level of the content of the middle ear cavity showed elevated levels, not only in the experimental ear but also in the contralateral. This increased level of histamine was recorded as long as 24 hours after stimulation. Though the mechanisms involved are not known, new ideas about the initiation of otitis media with effusion are inferred.