Jennifer

Rubin,

MD

#{149} Hugh

D. Curtin,

MD

Malignant External of CT in Diagnosis

Malignant external otitis is a severe bacterial infection of the bone and soft tissues of the base of the skull that is frequently difficult to diagnose. The effectiveness of antibiotic therapy is likewise difficult to assess. Serial computed tomographic (CT) scans were obtained in 11 consecutive patients with malignant external otitis at time of diagnosis and periodically after conclusion of antibiotic therapy. All patients demonstrated abnormalities of the external auditory canal, with or without bone destruction. Soft tissue or fluid in the middle ear and mastoid, around the eustachian tube, and in the parapharyngeal space (both pre- and poststyloid) was seen in greater than 50% of the cases. While remineralization of bone was not seen, soft-tissue disease improved dramatically, and recurrence or persistence could be conroborated by detection of more extensive soft-tissue changes. By delineating the extraand intracranial extent of disease, serial CT scans enable one to make the diagnosis, determine the extent of infection, document recurrence, exclude progression, and confirm resolution of malignant external otitis. Index

terms:

mation

CT,

and

Ear, infection,

214.1211

eases,

CT, 211.1211 211.20,

Mastoiditis,

Ear,

212.20

214.26

#{149}

inflam-

#{149}

#{149} Mastoid, #{149} Skull,

dis-

12.20

Radiology

1990;

174:391-394

I

From

the

Departments

D.B.K.),

(V.L.Y.), Medicine, 15261.

Radiology

M

of Pittsburgh

University 968 Received

Scaife July

ed August 9, revision accepted September quests to V.L.Y. C

RSNA,

1990

and School

Hall, Pittsburgh. 10, 1989; revision

received 12. Address

September reprint

Medicine of PA request-

11; re-

#{149} Donald

external otitis is an infection of bone and soft tissues almost always caused by Pseudomonas aeruginosa. It occurs almost exclusively in the elderly patient with diabetes mellitus. The disease is manifest by severe unrelenting otalgia, headache, and purulent otomnhea unresponsive to topical antibiotics (1,2). A markedly elevated erythrocyte sedimentation rate (ESR), granulation tissue in the extennal auditory canal, and evidence of bone destruction on computed tomography

ALIGNANT

(CT)

scans

are

important

objec-

tive data for making the diagnosis (3,4). The diagnosis is confirmed by recovery of P aeruginosa from the external canal or bone and exclusion of the presence of a malignant neoplasm. Beginning as an area of granulation tissue at the bone-cartilage junction of the

external

auditory

canal,

the

infec-

tion may progress to chondnitis and osteomyelitis extending posteriorly into the mastoid, anteriorly into the temporomandibular joint, or medially toward the petrous apex. Most commonly, however, the inflammation spreads infenionly via the fissures of Santorini to involve the soft tissues inferior to the temporal bone. The ability to delineate normal fat planes, particularly those of the area infenior to the temporal bone, makes CT an ideal tool for evaluating malignant external otitis (5). The sensitivity of CT in diagnosis and follow-up of the disease has not been established. Strashun et al reported that CT had a sensitivity of only 30% at the time of clinical presentation (6); however, their assessment was confined

to

elitis

and

not

of Otolaryngology

(H.D.C.),

L. Yu, MD

B. Kamerer,

MD

Otitis: Utility and Follow-up’

comitant potential (JR.,

#{149} Victor

permit

the

documentation

did

not

of

take

soft-tissue limitation

into

account

con-

abnormalities. of CT is that

A it does

differentiation

of

external otitis and carcinoma. two cases have been reported malignant

external

osteomy-

otitis

malignant

incided with or predated the presence of squamous cell carcinoma of the skull base (7,8). Most articles have reported that the

MATERIALS

AND

METHODS

Serial CT scans were obtained in i i consecutive patients with malignant external otitis seen at the Eye and Ear Hospital of Pittsburgh between 1986 and 88. CT was performed on a 9800 scanner (GE Medical Systems, Milwaukee) with use of intravenous contrast material. The section thickness was 1.5 mm through the temponal bones through

and skull base the nasopharynx.

and

3 mm Soft-tissue

and

bone algorithms were performed in all cases. Patients underwent an average of three examinations, including one at the time of initial presentation. Nine of the 1 1 patients (82%) were rescanned at least 8 months

after

therapy

(range,

months).

All

the

Each

study

(a) external

studies

same

head

was

suture

of antibiotic

months;

of the

mean, were

and

assessed

auditory

with or without tension beneath

crossing mastoid

completion

8-37

preted by the ogist (H.D.C.).

nadiol-

evidence

of

abnormality

bone destruction, the temporal

bone,

(b) ex(c)

(d) fluid in the (e) petrooccipital

(f) intracranial

involvement,

17.2

inter-

neck

for

canal

of the midline, or middle ear,

ex-

tension, (g) mass effect in the nasopharynx, (h) involvement of the clivus, (i) extension

into

parapharyngeal involvement, eustachian

In fact, in which

apparently

abnormalities on CT scans persist despite the obvious clinical remission of disease (4-6,9,10). However, Gold et al concluded that serial CT scans could aid in evaluating the effectiveness of therapy, given its ability to demonstrate the resolution of central soft-tissue disease (ii). We analyzed 33 sequential CT scans in 1 1 patients in an attempt to identify diagnostic features of this disease and to establish the radiologic features of both the eradication of disease as well as its persistence or recurrence.

the

pre-

and

poststyloid

space, (j) masticator and (k) disease around tube.

space

the

co-

Abbreviations: tion

ESR

erythrocyte

sedimenta-

rate.

391

Figure 1. (a) Axial section through the temporomandibular posterolateral margin of the condyle (arrow). (b) Fat planes to the temporomandibular joint have resolved. The appearance tamed at an angle different from that in a.)

RESULTS A total of 33 CT scans were obtained, with an average of three scans per patient (range, 1-5). Two patients did not undergo follow-up studies. One died of causes unrelated to malignant external otitis at 1 year after treatment. The othen had no evidence of clinical disease at 49 months after therapy, but because of hen general debilitated condition, she was unable to return for follow-up scanning. Findings at the time of diagnosis are listed in descending order of frequency in the Table. Clinical cure predated madiologic regression in all cases. Progressive resolution of soft-tissue disease (in contrast to osseous involvement) was noted at varying intervals after the completion of antibiotic therapy. One patient had severe temponomandibulan joint tenderness at presentation with extensive soft tissue in the area of the right temporomandibular joint on CT scans (Fig la). Hen joint tenderness progressively resolved, and CT scans obtained at 4 and 12 months after treatment showed progressive resolution of the inflammatory process (Fig ib). Two patients had evidence of obliter-

a.

(a) Scan

2. normal

the months

shows increased fat planes beneath the

after

therapy,

the

fat

planes

Progression

of disease

despite

antibi-

the

penitubal

therapy

fat

showed

planes

less

on

CT

obliteration

parapharyngeal

of fat in both the parapharyngeal and penitubal areas (Figs 2b, 3b). Soft tissue in the external auditory canal, with or without bone destruc-

junction

tion,

py

was

initial cessful

a near

finding

in

tissue

contour

restoration

masticator cases

of (Fig

space at

4b).

was

diagnosis

chitecture of the normal were initially inappanent cerned after treatment 392

#{149} Radiology

the

normal

Disease

noted (Fig

5a).

subtemporal

with

hyperbaric

oxygen

(Fig 3b). The patient well, with no evidence re-

softin

in

and

areas (Fig 3a). However, these findings improved after 12 weeks of tobnamycin and piperacillin administration in con-

at

CT examination (Fig 4a). Sucantibiotic therapy frequently

suited

the

universal

month around

The

midline

fat planes that could be dis(Fig Sb).

follow-up.

initially

the 27% of an-

at the

and (Section

lateral ob-

defined

biotic

the

soft tissue

tissue in the retropharyngeal area and obscuration of skull base, close to the eustachian tube (arrow). (b) At 12 immediately beneath the skull base (arrow) are better

scans obtained at the time of presentation (Figs 2a, 3a). Subsequent CT scans obtained following completion of anti-

of

shows

U.

Figure

otic therapy was also documented. One patient with persistent disease after two 6-week courses of oral therapy with ciprofloxacin and nifampin had, on CT scans, more extensive soft tissue around the eustachian tube as well as

ation

joint

abutting the condyle is now normal.

sels,

had the but

completion

veloped reelevation

with (Fig

The evidence tip

clear 6a).

One

at 24-

patient

disease

and

great

delineation

of antibiotic

recurrent of his

other of

mastoid

thera-

is currently of disease

month therapy,

yes-

of the after

fections

the he

tamed at this time showed crossing of the midline and obscuration of fat medial to the lateral pterygoid muscles (Fig 6b). We further divided our patients into two groups based on the severity of disease as defined by (a) evidence of cranial nerve palsies on examination, (b) an ESR greater than 80 mm/sec, and (c) symptoms present for 12 weeks on longer before the institution of definitive antibiotic therapy. The seven patients with more severe disease at the time of presentation had a greater number of abnormal findings (Table) on CT scans (range, 6-10; mean, 8) compared with the four patients whose in-

de-

symptoms as well as ESR. A CT scan ob-

appeared

less

2-4; mean, 3). There normal finding seen in those with severe presence of intracranial

virulent

(range,

was no single abmore frequently infection. The extension,

February

1990

however, indicated a particularly recalcitrant form of the disease, as seen in the one patient who required four courses of antibiotics in conjunction with hyperbaric oxygen treatments before clinical and bacteriologic cure could be demonstrated (Fig 7).

DISCUSSION

b. Figure ryngeal

3.

(a) Obscuration

of the normal fat planes around the eustachian tube and parapharegion (black arrow) (compare with opposite side). This image represents progression of disease compared with a previous CT scan (not shown). The torus tubarius on the normal side (white arrow) is seen posterior to the eustachian tube orifice. (b) Considerable improvement in the fat beneath the skull base is seen 15 months after the completion of antibiotic therapy. Some residual abnormality (arrow) persists in the area around the eustachian tube.

Much of the experience recounted in the literature with malignant external otitis has involved plain radiography and plunidirectional tomography. These techniques can demonstrate bone destruction, the presence of soft tissue in the external auditory canal, and increased density of the mastoid air cells, but they are inadequate for documenting infnatemponal or intracranial disease extension (5,12,13). Nuclear medicine studies, such as bone scanning with technetium-99m methylene diphosphate, have frequently been

used

to

confirm

the

clinical

di-

agnosis of malignant external otitis (6,9-ii,i3-i6). A mere 10% increase in osteogenic activity is sufficient for the detection of a lesion by means of bone scanning (6). The modality is extremely sensitive,

but

its

usefulness

is impaired

by its low specificity. Since the tracer accumulates at sites of any osteogenic activity, a “positive” scan may be seen in inflammatory disease, carcinoma, temponomandibular joint disorder, or fracture. In one study, radiologists blinded to the patients’ diagnosis were unable to differentiate scans of patients with malignant external otitis from those

with

simple

severe

external

otitis

Additionally, the bone scan memains positive despite the clinical nesolution of disease, limiting its utility in follow-up (4,6,9,13-15). (17).

a. Figure pare part

b. 4. (a) Soft with opposite of the external

tissue

(arrow)

fills

the

normally

air-filled

side). There is also more superficial ear. (b) After therapy, the external

external

soft-tissue canal is air

auditory

change filled

in the (arrow).

canal

(com-

Gallium

posterior

scanning

has

also

been

used

for evaluation because activity in malignant contrast to the minimal

of the intense external otitis in uptake of galli-

um

the

normally

seen

in

head

region.

Like Tc-99m bone scanning, Ga-67 citrate studies are characterized by low specificity and imprecision in the anatomic localization of disease. Although it has been suggested that serial gallium scans may help in predicting clinical resolution (13-15), recurrent on persistent disease has been documented in patients with normal gallium studies (9,iO,18). This is especially true in deeper lesions close to the nasopharynx and central skull base. Magnetic resonance (MR) imaging has

been

nant

used

external

limited.

Ghenini

imaging a.

Figure space planes

Volume

b.

5.

(a) Axial

(arrow) (arrow).

174

section shows obscuration (compare with opposite side).

of the normal (b) Posttreatment

tion fat planes in the masticator return of the normal fat

although sponse imaging

#{149} Number

2

in

of

is

found

extent difficult

to antibiotics alone.

malig-

experience MR

to CT in demonstra-

anatomic it was

of

but

et al (19)

superior the

evaluation

otitis,

with Further

of to

disease,

establish use

of

neMR

experience

Radiology

#{149} 393

with MR imaging evaluation is needed, including investigation of the role of gadolinium and comparison with CT. CT has been reported to be insensitive in early cases of malignant external otitis (6), although in that study diagnostic criteria were restricted to the documentation of bone changes. In our study, all i 1 patients had abnormal findings on CT scans at the time of presentation as required for inclusion into the study; thus, the utility of CT in diagnosis was not assessable. Features on the initial CT scans included nonspecific findings such as aneas of soft-tissue density in the external canal (Fig 4a) and fluid in the mastoid or middle ear (Fig 5a). More specific and ominous findings included bone erosion, obliteration of fat planes beneath the temporal bone, parapharyngeal space involvement (Fig 3a), masticaton space disease (Fig Sa), mass effect in the nasopharynx, clivus erosion, and intracranial extension (Fig 7) (Table). As in earlier studies, we confirmed that certain abnormalities on CT scans, particularly bone destruction, did not return to normal despite the remission of infection and symptoms. However, there appeared to be a distinct subset of CT findings that did resolve with eradication of the bacterial infection. Specifically, fluid in mastoid or middle ear, as well as soft-tissue abnormalities beneath the temporal bone and skull base, disappeared or substantially improved within several months following antibiotic therapy. Since symptoms are frequently alleviated soon after the institution of antibiotics, there is uncertainty about the optimal duration of antimicrobial therapy. Thus, the resolution of soft-tissue disease on CT scans is an important objective marker in the symptom-free patient that may assist physicians

in

deciding

when

to

discon-

tinue antibiotic therapy. Malignant external otitis is notoriously difficult to eradicate, with a recurnence rate of approximately 20% in the larger clinical series (3). Our two patients with recurrent or persistent disease

as manifest

by

recurrence

of

headache and neelevation of ESR showed progressive soft-tissue changes at CT (Figs 3a, 6b). Thus, static CT scans may

be

useful

disease,

in

while

excluding

of disease

diagnosis

otitis

but

the

severity

394

S

of

also

further of

Radiology

the

malignant aid infectious

external in

assessing process.

b.

Figure 6. (a) Scan shows obscuration area of the great vessels (single arrow),

of fat planes around the mastoid tip (two arrows) and but the midline is clear, as are the fat planes medial

to the

arrow).

lateral

toid

tip

to the

pterygoid

has

muscles

improved,

lateral

sion

pterygoid

be obtained disease.

repeat

to rule In

the

posttherapy

is obscured

out

scans

auditory

tiguous.

findings

canal

are

is often

Clinically, of

whereas sent

ma.

the

severe

malignant

pain in

is usually early

2.

3.

4. 5.

6.

7. 8.

9.

arrow).

abnormality (arrow),

around and

the

the fat

mas-

medial

of

unlikely

not

to

exexter-

possible.

stages

pain external minimal

is charotitis,

Figure

10.

1 1.

U

Cohen D, Friedman P. The diagnostic critena of malignant external otitis. J Laryngol Otol 1987; 101:216-221. Cohen D, Friedman P. Eilon A. Malignant external otitis versus acute external otitis. Laryngol Otol 1987; 101:211-215. Rubin J, Yu VL. Malignant external otitis: insights into pathogenesis, clinical manifestations, diagnosis. and therapy. Am J Med 1988; 85:391-398. Rubin J, Yu VL, Stool S. Malignant external otitis in children. J Pediatr 1988; 113:965-970. Curtin HD, Wolfe P. May M. Malignant external otitis: CT evaluation. Radiology 1982; 145:383-388. Strashun A, Nejatheim M, Goldsmith SJ. Malignant external otitis: early scintigraphic detection. Radiology 1984; 150:541-545. Chandler JR. Pathogenesis and treatment of facial paralysis due to malignant external otitis. Ann Otol 1972; 81:648-658. Matucci KF. Setzen M, Galantich P. Necrotizing otitis externa occurring concurrently with epidermoid carcinoma. Laryngoscope 1986; 96:264-266. Gherini SG, Brackmann DE, Bradley WG. Magnetic resonance imaging and computerlied tomography in malignant external otitis. Laryngoscope 1986; 96:542-548.

12.

13.

Axial section through superior bone shows a small area of intrainvolvement (arrow).

7.

temporal cranial

on ab-

of cancino-

References 1.

(open

the midline

patient,

We have observed, however, that in malignant external otitis, bone erosion may occur in several areas with intervening “skip” regions, whereas, in cancinoma, bone erosions are usually conactenistic

the

should

progression

influence management. It should be noted that nadiologic differentiation between malignant ternal otitis and carcinoma of the nal

Although

crosses

If symptoms CT

asymptomatic CT

(b)

now

that CT scans be obof diagnosis prior to and at the conclutherapy.

on recur,

tissue

muscles

of antibiotic

persist

(open

abnormal

We recommend tamed at the time antibiotic therapy

recurrent

progression

on CT scans in a symptomatic patient can support the decision to continue or reinstitute antibiotics. When classifying our patients into groups based on the severity of disease, we found that those with a more virulent infection had more abnormalities of the initial CT scan than did those with a milder infection. Thus, the CT scan may not only contribute to the accurate

a.

Mendelson

MH,

Meyers

BR, Hirschman

SZ,

Shapiro ER, Parisier SC. Treatment of invasive external otitis with cefsulodin. Rev Infect Dis 1984; 6:698-704. Gold S. Som PM, Lawson W, Lucente FE, Mendelson M, Parisier SC. Radiographic findings in progressive necrotizing “malignant” external otitis. Laryngoscope 1984; 94:363-366. Mendez G, Quencer RM, Donovan Post MJ, Stokes NA. Malignant external otitis: a radiographic-clinical correlation. AJR 1981; 91:960-964. Ostfeld E, Aviel A, Pelet D. Malignant externat otitis: the diagnostic value of bone scmtigraphy. Laryngoscope 1981; 91:960-964.

14.

Garty

15.

clide diagnosis. evaluation and follow-up of malignant otitis externa (MOE): the value of immediate blood pool scanning. J Laryngol Otol 1985; 99:109-115. Parisier SC, Lucente FE, Hirschman SZ, Som

I. Rosen

PM, Arnold

16.

17.

18.

19.

G, Holdstein

LM, Riffman

Y.

JD.

The radionu-

Nuclear

scan-

ning in necrotizing progressive “malignant” external otitis. Laryngoscope 1982; 92:10161020. Reiter D, Bilaniuk LT, Zimmerman RA. Diagnostic imaging in malignant otitis externa. Otolaryngol Head Neck Surg 1982; 90:606609. Levin WJ, Shary JH, Nichols LT, Lucente FE. Bone scanning in severe external otitis. Laryngoscope 1986; 96:1193-1195. Kraus DH, Rehm SJ, Kinney SE. The evolving treatment of necrotizing external otitis. Laryngoscope 1988; 98:934-939. Gherini SC, Brackman DE, Bradley WG. Magnetic resonance imaging and computerized tomography in malignant external otitis. Laryngoscope 1986; 96:542-548.

February

1990

Malignant external otitis: utility of CT in diagnosis and follow-up.

Malignant external otitis is a severe bacterial infection of the bone and soft tissues of the base of the skull that is frequently difficult to diagno...
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