muscle and tendon. Other structures arising in whole, or in part, from the second arch include the mandibular condyle, styloid process, and facial nerve canal.83Ossicular development occurs simultaneously with the formation and differentiation of the middle ear cavity and its out- pouchings. The second half of this interval is primarily concerned with ossification, the ossicles having achieved adult size by the 15th week.84Formation of the stapes is not complete until week 38.85 Early in gestation the stapes primordium is pierced by the stapedial artery and is separated from the developing facial nerve and pyramidal eminence (laterohyale) by the interohyale, which becomes the stapedius tendon.86The stapes foot- plate has two layers: the tympanic portion, which is derived from the second brachial arch, and the vestibular portion (with its annular ligament), which develops from the otic capsule.81,84,85 The ossicles change little during life and, similar to the otic capsule, demonstrate a limited capacity for repair.
The TM and the supportive tympanic ring are formed by the 18th week of gestation. Portions of the TM are derived from all three germ layers. The outer epithelial layer is derived from the ectoderm of the first branchial groove (external auditory meatus). The middle fibrous layer is derived from the mesoderm, which insinuates itself between the tympanic cavity and the first branchial
groove. The inner mucosal layer is derived from the endo- derm of the first pharyngeal pouch.30
The tympanic ring (tympanic bone) is formed in mem- branous bone from four ossification centers. It is virtually completely developed by the 15th week of gestation.
There is a defect in the ring superiorly, which is known as the notch of Rivinus. The TM inserts in this location. The tympanic ring provides the scaffolding for the TM. The TM is relatively horizontal at birth and does not assume the adult vertical orientation until 3 years of age.81The tym- panic ring also contributes to the development of the styloid process. It is this tympanic bone that forms the sides and floor of the bony EAC as it elongates.
human immunodeficiency virus (HIV) patients.87Aggres- sive fungal or pseudomonas mastoiditis may be seen, how- ever, in severe HIV cases.88,89
As indicated in the previous paragraphs, middle ear effusions occur with both AOM and COM. Children are predisposed to AOM and effusion for several reasons. The eustachian tube in children is inherently dysfunctional due to its relatively horizontal orientation and shorter length. Obstruction of the eustachian tube by prominent adenoidal tissue, release of inflammatory mediators from adenoidal mast cells and adenoidal tissue acting as a reservoir for bacteria are all mechanisms for the develop- ment of middle ear effusion.90
The reader is cautioned that identification of debris suggestive of inflammatory disease within the mastoid is common, especially in children.91Perhaps 10 to 15% of children and a substantial percentage of adults examined with MRI for other reasons will have heterogeneous T2-weighted hypersignal within the peripheral mastoid and middle ear proper despite the absence of a history of otitis media. The reason for this is unclear, but the observer should not misconstrue this common finding to be necessar- ily indicative of clinically significant inflammatory disease.
A common error is to refer to abnormal signal in this region as mastoiditis, a clinical diagnosis. I refer to this type of finding as “nonspecific mastoid debris” and rec- ommend CT, if clinically indicated.
Acute Otomastoiditis and Complications
Most cases of acute otomastoiditis occur in children and manifest clinically as otalgia, fever, and erythema/edema of the TM. The middle ear and mastoid are generally considered an extension of the upper respiratory tract and subject to bacterial invasion via the eustachian tube.
Mucoperiosteal inflammation results initially in serous effusion, which may become mucoid or purulent.92Fluid levels are commonly demonstrated at CT provided that there are two orthogonal planes (axial and coronal).
Previously, we referred to the aditus ad antrum, an inher- ently narrow communication between the epitympanum (attic) and the mastoid antrum. Swollen mucosa may block the aditus, which traps secretions in the peripheral mastoid with subsequent development of AOM. Effective therapy is crucial at this juncture.
AOM is most often caused by bacterial infection. Strep- tococcus pneumoniae(pneumococcus) and Haemophilus influenzaeaccount for 65 to 80% of cases.93The latter agent is less common but more aggressive and associated with a higher incidence of meningitis.88Proteusand Pseudomonas species are less common culprits.94The development of antibiotics, of course, resulted in a remarkable decline in the incidence of the complications of this disorder.
Recently, however, there has been somewhat of an upsurge
due to drug-resistant organisms (penicillinase-producing Streptococcus pneumoniaeand beta-lactamase-producing strains of Moraxellaand Haemophilus) and a change in microbial flora.95
Mycotic disease is unusual. These infections may be invasive when they occur in the immunocompromised host.96 Type I infections are limited to the EAC (otitis externa). Type II infections involve extension into the mastoid cavity (mastoiditis). Type III is invasive mastoidi- tis with facial palsy, and type IV infection is a fulminant skull base osteomyelitis.97–99
Tuberculous otomastoiditis (TOM) is increasing in prevalence due to the rising incidence of immunocom- promised hosts. There are many possible methods of inoculation, but most commonly it is either hematogenous or extends directly from the nasopharynx. Classically, these patients present with chronic painless otorrhea and an intact TM; however, wide variations in presentation have been recently described.100,101Pain, purulence, and EAC/TM involvement are all now considered to be common presentations. Ossicular erosion, aggressive tumor-like middle ear/mastoid destruction, and lymphadenopathy are all associated with this disease (Fig. 3.32). The lym- phadenopathy commonly involves the postauricular region but may involve the parotid gland or other upper cervical lymph nodes.100TOM should be considered in any patient regardless of immune state who fails to respond to antibacterial therapy.102,103Peridural disease and facial nerve involvement are especially common in these patients. In fact, the classic clinical triad of TOM is multiple TM perforations, “pale” granulation tissue, and facial paralysis.104 Atypical mycobacteria are most frequently associated with chronic intractable granulation tissue.
Often, these patients are also immunosuppressed.105 Complications of acute otomastoiditis include coales- cent mastoiditis, subperiosteal abscess, Bezold abscess, meningitis, parenchymal/extracerebral abscess, empyema, dural sinus occlusive disease, otitic intracranial hyperten- sion (otitic hydrocephalus), facial nerve involvement, labyrinthitis, and petrous apicitis. Occasionally, these com- plications may occur superimposed upon chronic otitis media. Such superinfection is especially dangerous when CH is present. In these cases, careful study of the tegmen tympani and sigmoid sinus plate is required for reasons that will be described in subsequent sections of this chap- ter. When this type of bony defect is present, evaluation with MRI (and MR angiography [MRA]) is strongly recom- mended.106,107
Coalescent Mastoiditis
Fortunately, the vast majority of patients with acute otomastoiditis are cured after a course of antibiotics, and no imaging procedures are necessary.11Should CT or MRI
be performed at this time, nonspecific debris would be identified, typically associated with several fluid levels (Fig. 3.33). CT will demonstrate the integrity of the mas- toid septa, ossicular chain, and the internal and external mastoid cortex.108The turning point for these patients is when mucoperiosteal disease becomes bone disease with enzymatic resorption of mastoid septa and the develop- ment of an intramastoid empyema. This is referred to as coalescent mastoiditis.109,110Osteoclastic dissolution of the pneumatic cell walls is likely a result of hyperemia, local
acidosis, and subsequent calcium dissolution.84,92The di- agnosis of coalescent mastoiditis often requires the demon- stration of subtle bony changes, which must be carefully sought in all AOM patients; therefore, high-resolution CT is the best imaging modality available during this interval (Fig. 3.34, Fig. 3.35,and Fig. 3.36). Subtle evidence of alternations of these mastoid septations may be clini- cally significant and reflect antibiotic failure. Often a com- parison to the opposite side is needed in this regard (despite the fact that mastoid pneumatization is not always
Chapter 3 The Middle Ear and Mastoid
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A
B
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Fig. 3.32 Tuberculous otomastoiditis with parenchymal abscess. (A)Axial and (B)coronal computed tomography images reveal a destructive process sparing the inner ear. (C)Contrast-enhanced T1-weighted magnetic resonance image reveals a thick rind of enhancement surrounding the mastoid debris (single arrow) as well as a mature abscess in the periphery of the cerebellar hemi- sphere (double arrows).
symmetric). Fortunately, coalescence is usually not subtle, and the diagnosis will be obvious. Importantly, when coa- lescent disease is the result of aditus obstruction or perhaps attic blockade (isthmus obstruction), the TM and middle ear may appear normal otoscopically. This is referred to as latent mastoiditis due to the paucity of clinical clues.92
Subperiosteal Abscess
In addition to evaluating the status of the mastoid septa, the internal mastoid cortex and external mastoid cortex must be carefully examined. A subperiosteal abscess typi- cally develops via direct extension of the inflammatory debris through a defect in the external mastoid cortex.
Such collections are often palpable (Fig. 3.37and Fig. 3.38).
They are usually postauricular due to the thin trabecular bone in this region (Macewen’s triangle).11Abscess forma- tion should not be confused with the edema, which occurs in this location secondary to thrombosis of mastoid emis- sary veins (Griesinger’s sign). Preauricular abscess forma- tion is possible if the infection preferentially spreads along the zygomatic root. Even more rare is the Luc’s abscess which develops deep to the temporalis muscle.
Bezold Abscess
The Bezold abscess is analogous to the superiosteal abscess occurring when the bony defect is seen at the mastoid tip (instead of the external mastoid cortex) medial to the insertion of the posterior belly of the digastric (digastric groove) and sternocleidomastoid muscle. This results in inflammatory debris extending inferiorly along the soft tissues of the neck, often with formation of an abscess (Fig. 3.39).111,112,113Importantly, the inflammatory lesion most commonly lies within the posterior cervical space deep to the sternocleidomastoid muscle, resulting in the absence of a clinically palpable fluctuance.113Pneumatiza- tion of the mastoid tip is a predisposing factor (also anal- ogous to petrous apicitis in this regard, vide infra); therefore, this process is more common in adults than children. For Fig. 3.33 Uncomplicated acute otomastoiditis. (A)Axial and (B)coronal computed tomography images. There is diffuse debris throughout the mastoid. Note the preservation of the integrity of the mastoid septations as well as the internal and external mastoid cortices.
Fig. 3.34 Acute coalescent mastoiditis. Magnified axial computed tomography image reveals diffuse mastoid debris with fluid level (arrow). All of the septations are thin and irregular. There is a sigmoid sinus plate defect (outlinedarrows), which must be viewed with suspicion.
A B
these reasons, temporal bone CT is recommended for unexplained neck abscesses. The potential exists for this abscess to extend inferiorly as far as the mediastinum.
Meningitis, Abscess, and Empyema
Defects in the internal mastoid cortex are of obvious con- cern, as this leaves the underlying dura adjacent to the sigmoid sinus and cerebellum directly exposed to the inflammatory process. Dangerous intracranial complica- tions such as sigmoid sinus thrombosis, intracerebral or
extracerebral (perisinus) abscess formation, and meningi- tis can occur via direct extension, hematogenous dissemi- nation, or retrograde thrombophlebitis.114 The latter is considered to be the most common mode of spread.
An abscess is a collection of pus lined by a fibrous cap- sule. When it occurs in the subdural or epidural compart- ment, it must be distinguished from empyema, which spreads out over a wider area. Individuals with a subdural empyema (SDE) typically have meningitis as well. SDE is a much more likely complication of sinusitisthan otomas- toiditis.115Sterile subdural collections (hygroma) are also
Chapter 3 The Middle Ear and Mastoid
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B
Fig. 3.35 Coalescent mastoiditis. (A)Axial computed tomography image reveals diffuse mastoid debris with extensive coalescent changes in mastoid septations (arrows). (B)Axial T2-weighted MRI confirms debris but not the changes in the bony septations. (C)Coronal-enhanced T1-weighted MRI reveals that debris enhances.
associated with meningitis in the absence of abscess for- mation. Rarely, spread of inflammatory disease to the meninges occurs along normal anatomical structures such as the petrosquamous suture and petromastoid canal (subarcuate artery).11Proteus, Pseudomonas, and Staphylo- coccus species are often isolated in these advanced cases.116Abscesses may occur in the middle cranial fossa, but are much more common in the posterior fossa due to osseous destruction in the Trautmann triangle between
the sigmoid sinus plate and the sigmoid sinus (Fig. 3.32, Fig. 3.40,and Fig. 3.41).92
Unexplained episodes of meningitis especially in chil- dren typically provoke a search for a parameningeal focus, and history/findings compatible with otitis media are care- fully sought in this context. Detailed CT investigation of the bony margins of the temporal bone is required. Congenital fistulas, often associated with inner ear malformations, may be present (see Chapter 5). These patients typically Fig. 3.36 Coalescent mastoiditis, left ear. (A)Magnifed axial computed
tomography (CT) image of the normal right ear. Note the normal pneumatization and well-defined septations. (B)Magnified axial CT of
the left ear demonstrates debris (*) in the peripheral mastoid in a patient with otalgia and fever. Note the loss of mastoid septations, confirming coalescent disease. The internal and external mastoid cortex is intact.
A B
A B
Fig. 3.37 Coalescent mastoiditis, subperiosteal abscess. (A)Axial com- puted tomography (CT) image. Debris throughout mastoid with thin- ning and poor definition of mastoid septations (compare with opposite
side). Focal defect in external mastoid cortex (arrow). (B) Axial CT image, postcontrast. Low-density mass representing subperiosteal abscess. Note small air bubble (arrow).
have CSF otorhinorrhea. In several published reports, surgi- cal investigation of focal cortical defects along the posterior and middle fossa surfaces of the temporal bone has revealed arachnoid granulations as the cause of recurrent meningitis in a significant number of cases117(see Chapter 5). Hyrtl’s (tympanomeningeal) fissure normally closes at 24- to 26-week gestation. If persistently patent, this structure may also be responsible for spontaneous CSF otorrhea.
These defects are infralabyrinthine adjacent to the round window.118Spontaneous CSF otorrhea may also be caused by significantly larger defects and be associated with menin- goencephalocele. These patients often present with CHD.119 Meningitis is the most common intracranial complica- tion of acute otomastoiditis.120Proteus, Pseudomonas, or Staphylococcus species are usually isolated. A brain (parenchymal) abscess usually involves the temporal lobe
Chapter 3 The Middle Ear and Mastoid
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Fig. 3.38 Coalescent mastoiditis with subperiosteal phlegmon and lymphadenopathy. (A,B)Axial computed tomography (CT) images reveal diffusely eroded mastoid septations, indicating coalescent disease, with a large defect in the external mastoid cortex (arrow).
(C)Corresponding axial CT image with soft tissue window reveals phlegmonous debris (arrow) rather than subperiosteal abscess, which typically occurs under these circumstances. (D)Axial CT image through neck soft tissue reveals multiple pathologic lymph nodes (arrows).
A
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B
D
and presents with symptoms of a mass lesion. Anaerobes such as Bacteroidesand Fusobacteriummay be the culprit.
Interestingly, a brain abscess is often a complication of chronic rather than acute otitis. Epidural and subdural abscess often occurs adjacent to the sigmoid sinus and is strongly associated with bone erosion. Middle fossa extraaxial collections often exhibit somewhat limited extension due to the firm attachment of the dura to the arcuate eminence, a convexity corresponding to the site of the superior semicircular canal.120
Dural Sinus Occlusive Disease
Dural sinus occlusive disease (DSOD) is an extremely dan- gerous and potentially fatal complication of AOM that
may occur via direct extension or result from erosive osteitis and retrograde thrombophlebitis via emissary veins. The majority are associated with epidural abscess.
Perisinus inflammation may induce formation of mural thrombus within the sinus lumen secondary to pressure effects, causing the adherence of fibrin and platelets.121,122 This mural thrombus becomes infected and propagates to form an obliterating thrombus.94Some consider the formation of a thrombus to be a protective mechanism attempting to limit and localize the infection. Severe headaches, high spiking fevers, postauricular edema, sixth nerve palsy, and mental status changes herald the diagno- sis clinically. Alterations of posture may be catastrophic for these patients. Antibiotic therapy is the cornerstone of treatment.123Anticoagulation is controversial. Surgical Fig. 3.39Mastoiditis–Bezold abscess. (A)Axial computed tomogra- phy (CT) image reveals diffuse mastoid debris with a large sigmoid sinus plate defect (arrow). (B)More inferior image at the mastoid tip reveals a large area of erosion with a large lateral bony defect (arrow). (C)Axial CT image immediately subjacent to the mastoid tip reveals a classic Bezold abscess (arrow).
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exploration is often needed. Aspiration of the clot may yield the necessary restoration of flow, but incision into the sinus and removal of the clot may be necessary. Liga- tion of the sinus is rarely needed, but it has been used to control septic emboli.120
Due to anatomic proximity, involvement of the sigmoid/
transverse sinus is most common. In many patients, a clot may propagate antegrade into the internal jugular vein or retrograde to the torcula and superior sagittal sinus.124 Extension along emissary veins to the subcutaneous tissues
Chapter 3 The Middle Ear and Mastoid
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A
B Fig. 3.40 Coalescent mastoiditis with temporal lobe parenchymal
abscess. (A)Axial computed tomography (CT) image at bone window reveals diffuse middle ear debris sparing the inner ear. (B)Axial CT image at soft tissue window reveals a well-defined ring-enhancing mass in the middle cranial fossa, consistent with abscess (arrow).
Fig. 3.41 Acute otomastoiditis, cerebritis. (A)Axial and (B)coronal contrast-enhanced T1-weighted magnetic resonance images reveal mastoid debris with a heterogeneous intensely enhancing area (arrow) in the adjacent temporal lobe.
A B
may also occur. Furthermore, the reader should be aware of the anatomic proximity of the superior and inferior petrosal sinuses, which drain the cavernous sinus. Clot propagation retrograde could thus have further dire clinical consequences. Systemic septic emboli and pulmonary thromboembolic disease also have grave implications.119,125 DSOD remains a difficult imaging diagnosis despite the advent of MRI (Fig. 3.42, Fig. 3.43,and Fig. 3.44).
Clinical suspicion is the single most important diagnostic element.126If examination of conventional spin echo im- ages reveals a flow void in the typical anatomic location of the sigmoid sinus, the diagnosis of occlusive disease is effectively excluded. Similarly, bright signal repre- senting flow-related enhancement (FRE) on gradient echo pulse sequences also lessens the likelihood of this diagnosis. Findings on spin echo images can be particu- larly perplexing due to the vagaries of flow phenomena.
In addition, gadolinium-enhanced T1-weighted images
may be confusing as a result of dose-related issues and due to thrombus enhancement, which occurs consis- tently in chronic cases, presumably secondary to the conversion of the clot into vascularized connective tissue.127 Enhancement with gadolinium also occurs commonly in normal casesdue to physiological slow flow.
When considering this diagnosis, the observer must take into account indirect factors such as absent flow void on spin echo images and absent FRE on gradient echo sequences. These findings are nonspecific, but should spark suspicion under certain clinical circumstances. On occa- sion, signal characteristics allow for direct visualization of the clot within the lumen of the sinus. This is perhaps most effective in the case of the acute clot (initial stage) on spin echo pulse sequences as the hypointensity elicited by deoxyhemoglobin can ordinarily be distinguished from the signal void produced by rapidly flowing blood. Slightly greater intensity of the clot may be appreciated on the first Fig. 3.42 Mastoiditis. sigmoid sinus occlusive disease. (A)Axial contrast-
enhanced T2-weighted MRI and (B)T1-weighted MRI reveals enhancing debris throughout mastoid in a patient with spiking fevers. (A)Abnormal
hypersignal (arrow) in the expected location of the sigmoid sinus and (B)an area of nonenhancement (arrow) centrally within the sigmoid sinus representing a thrombus.
A B
Fig. 3.43 Acute otomastoiditis, sigmoid sinus thrombosis. (A)Axial con- trast-enhanced computed tomography (CT) image reveals mastoid debris with a “vacant” nonenhancing sigmoid sinus (arrow). (B)Magnified axial CT, left ear, reveals coalescent disease (arrow) with thinning of the sigmoid sinus plate (arrow). (C)Axial contrast-enhanced CT image reveals lym- phadenopathy (arrows), more noticeable on the left. (D)Axial T2-weighted
MRI reveals hyperintense mastoid debris with a hypointense area in the vicinity of sigmoid sinus (arrow), representing an acute clot. (E)Sagittal contrast-enhanced T1-weighted MRI reveals a nonenhancing area (arrow), representing thrombosis. (F)Magnetic resonance venography confirms absent flow in the sigmoid sinus and internal jugular vein (arrow). (Courtesy of Deborah Shatzkes, MD.)