Mer, in 1967, was the first to describe use of an endoscope to view the anatomy of the middle ear.  He initially performed endoscopy through a tympanic membrane incision on cadavers and on a feline model. Endoscopy in human patients was only attempted through previously existing perforations. Despite his initial success, the endoscope had only limited use as an instrument to photograph the tympanic membrane.
Two decades would pass before Nomura popularized the idea of a surgical myringotomy in an intact drum to permit endoscopic examination of the middle ear structures.  Subsequently, direct endoscopy through the middle ear space has been used successfully (1) as an alternate procedure for second-look mastoidectomy, middle ear exploration for perilymphatic fistula, and limited removal of epitympanic cholesteatoma and (2) as an intraoperative aid to visualize the attic, eustachian tube, and sinus tympani.
In 1989, Kimura introduced the concept of endoscopy of the middle ear through the eustachian tube orifice.  This technique has not met with the same clinical success as transtympanic endoscopy because of the small image size provided by the scope, difficult orientation, and poor illumination. In a recent study, 25% of endoscopy attempts through the eustachian tube orifice were aborted because of local irritation, bleeding, thick mucus, and/or blocked view by bony spicules. Theoretically, when the difficulties of this technique are overcome, it may provide information pertaining to pathologies in the epitympanum, mesotympanum, and mastoid antrum, and it may allow assessment of ossicular chain mobility. For now, however, the authors find only the transtympanic route for middle ear endoscopy to be a clinically viable technique.
The ear is composed of external, middle (tympanic) (malleus, incus, and stapes), and inner (labyrinth) (semicircular canals, vestibule, cochlea) portions. The auricle and external acoustic meatus (or external auditory canal) compose the external ear. The external ear functions to collect and amplify sound, which then gets transmitted to the middle ear. The tympanic cavity (middle ear) extends from the tympanic membrane to the oval window and contains the bony conduction elements of the malleus, incus, and stapes. The primary functionality of the middle ear is that of bony conduction of sound via transference of sound waves in the air collected by the auricle to the fluid of the inner ear. The inner ear, also called the labyrinthine cavity, is essentially formed of the membranous labyrinth encased in the bony osseus labyrinth. The labyrinthine cavity functions to conduct sound to the central nervous system as well as to assist in balance. 
For more information about the relevant anatomy, see Ear Anatomy.
Surgical eradication of cholesteatoma uses canal wall down or canal wall intact techniques. The extent of the disease process dictates the choice of technique. For limited and readily removable disease, the canal wall up technique is frequently employed. Elimination of a mastoid bowl and improved ability for hearing reconstruction are the major advantages of the canal wall up technique. However, the main disadvantage of canal wall up mastoidectomy is the rate of recurrent disease, which may reach 40%. This high rate of persistent cholesteatoma is due to poor visualization of the middle ear regions that harbor residual disease, eg, the attic, eustachian tube, and sinus tympani. [5, 6, 7, 8]
The sinus tympani is the most frequent site of residual cholesteatoma. Endoscopic intraoperative visualization of these regions has been demonstrated to reduce recurrence of cholesteatoma in canal wall up mastoidectomy. In several series that used an endoscope to complement traditional microscopic techniques, the recurrence rate fell significantly (from 8.6% to 0%).
The high rate of residual cholesteatoma in canal wall up mastoidectomies mandates a second-look procedure to ensure freedom from residual disease. This procedure usually involves a standard postauricular approach under a general anesthetic with the same morbidity and a similar recovery period as the original operation.
McKennan was the first to use the endoscope for examining mastoid cavities in patients who had undergone a previous canal wall up procedure. If no residual cholesteatoma existed, the patients did not undergo a standard postauricular approach. Small residual cholesteatoma pearls were removed endoscopically. The discovery of a large cholesteatoma residual requires a standard postauricular approach for removal. McKennan found that patients experienced decreased postoperative morbidity, including a smaller incision, less postoperative swelling, reduced operative time, and reduced auricular numbness. He found a residual cholesteatoma rate of 17%. 
In a 1994 report, Rosenberg and colleagues further evaluated the sensitivity of performing second-look procedures with the endoscope, first using the endoscope to examine pediatric patients undergoing second-look procedures followed by a standard postauricular microscopic procedure.  The endoscopic findings correlated with findings during the open procedure. Other investigators have confirmed these findings and have concluded that an open second-look procedure might be unnecessary if no cholesteatoma is found during the initial endoscopic procedure.
Deep retraction pockets with attic cholesteatoma
Use of the endoscope has been extended beyond its use as a tool for diagnosing middle ear disease. Middle ear endoscopes have been used, in place of the operative microscope, for management of deep retraction pockets with attic cholesteatoma. The procedure, as described by Tarabichi in 2000, is that of a transcanal atticotomy.  Patients were carefully observed, on an outpatient basis, to assess for recurrence. Long-term follow up (mean 41 mo) of this procedure demonstrated a 10% recurrence rate. Any disease with extensive mastoid involvement must be handled in traditional fashion.
Ménière disease is characterized by episodic vertigo, hearing loss, tinnitus, and aural fullness. Episodic vertigo is the most debilitating symptom. Many patients respond well to medical management, including diuretics and salt restriction. Some cases, however, are refractory to treatment and require intervention for control of vertigo.
Various surgical treatments are available to help control vertigo, including labyrinthectomy, endolymphatic shunt procedures, and vestibular neurectomies; however, intratympanic gentamicin injection is an increasingly popular and less invasive alternative. With recent dosing techniques, vertigo control rates can be as high as 90% with hearing loss rates of 3%.
The main diffusion route of gentamicin into the middle ear is through the round window membrane. Studies have demonstrated that the round window membrane may be completely obstructed in 12% of patients and partially obstructed in an additional 17%. Endoscopy performed before instillation of gentamicin can identify the obstruction. Any adhesions near the round window can be removed with variously angled hooks. Performing this maneuver may aid diffusion of gentamicin into the inner ear, thereby assisting treatment effectiveness.
Diagnosis of perilymphatic fistulae
Diagnosis of perilymphatic fistulae remains a challenge. Although the most common presenting symptoms are the triad of tinnitus, vertigo, and hearing loss, these symptoms can occur in a variety of combinations. Presentation can be indistinguishable from that of Ménière disease. A clear antecedent event that results in the symptoms of a fistula is absent in 23-35% of patients, further complicating diagnosis. Additionally, the classic fistulae test is as variable as the presentation, providing positive results in 25-77% of patients. Even with strong clinical suspicion, the odds of finding a definite leak at exploration can be as low as 50%. Even if exploration is undertaken, distinguishing pooling of local anesthesia from true perilymph may be difficult.
Without a clear event or strong clinical history, the decision to surgically explore an ear suspected of harboring a perilymphatic fistula is difficult. This decision is especially confounded by the lack of a sensitive preoperative confirmatory test. As described in the American Journal of Otology, in feline models, Poe surgically created perilymphatic fistulas, which were easily visualized with middle ear endoscopes.  He followed these experiments with exploration of patients with a high clinical suspicion of perilymphatic fistula, finding no active fistulae, as reported in Laryngoscope. However, Poe placed blood patches transtympanically in 7 patients with strong suspicion. Half of these patients had symptomatic improvement.
Transtympanic middle ear endoscopy is an office-based procedure that can aid diagnosis of perilymphatic fistulae. The transtympanic technique provides excellent visualization of the round window and the oval windows, as can be seen in the image below. Additionally, this technique avoids welling of local anesthetic or fluid within the round and oval window niches. The use of the endoscope to determine the presence of fistulae can obviate the need for a more extensive surgical procedure.
Treatment of cerebrospinal fluid otorrhea
Cerebrospinal fluid (CSF) rhinorrhea results from an unwanted connection between the subarachnoid space and the temporal bone. Through this connection, the CSF has a pathway to the unsterile environment of the nasal cavity. The development of this connection may be spontaneous, due to traumatic injuries, or due to surgical complication. The fluid travels through the air cells of the temporal bone to the ear, through the eustachian tube to the nasal cavity. This leaves a patient at risk for meningitis as long as the connection persists. Treatment, which is based the cause, may consist of conservative management or may require surgical intervention. Traditionally, surgery involves a mastoidectomy and packing of the middle ear. Recently, endoscopy to close the eustachian tube has shown promise as an alternative when conservative management fails. 
Place the patient in the supine position and clean the external auditory canal of cerumen and debris. Apply topical phenol to the posterior inferior quadrant of the tympanic membrane. Then, inject the posterior canal skin with 1% lidocaine with 1:100,000 epinephrine. The authors do not routinely perform the canal injection when looking for perilymphatic fistulae.
Make a radial 2-mm myringotomy incision along the line of the previously anesthetized drum, as seen in the first image below. Direct the endoscopes into the middle ear and through the myringotomy site by watching the video monitor. The authors then use 1.2-mm diameter 0° and 30° endoscopes. The round window, oval window, and stapes suprastructure are easily visualized, as seen in the second image below. In cases of suspected perilymphatic fistulae, ask the patient to perform the Valsalva maneuver during direct visualization of the fissula ante fenestram and the round window region.
After endoscopy, place a Teflon patch on the myringotomy incision site. Remove this patch in 2 weeks.
Use McKennan's method to examine mastoid cavities for residual cholesteatoma in second-look procedures. Perform this procedure while the patient is under a general anesthetic in the operating room. Make a 1-cm stab incision in the postauricular region. Next, place an aural speculum in the incision. If bony regrowth is present, use a drill to provide an opening in the mastoid cortex, thus allowing passage of the endoscope. Use the 30° and 0° endoscopes to view the mastoid cavity. If any cholesteatoma is found, the authors convert the operation to an open procedure.
Potential complications of this procedure include excessive heat and discomfort from the light source. In addition, a risk to the ossicular chain and tympanic membrane exists. The authors have encountered no complications with use of these techniques.
Middle ear endoscopy is a minimally invasive office-based procedure that has demonstrated an important adjunctive role in the management of otologic disease. Middle ear endoscopy has the potential to decrease both patient morbidity and cost without compromising results. Operatively, the use of middle ear endoscopy can complement traditional microscopic mastoid surgery to prevent recurrence and further surgery.