Charles R. Souliere, Jr., M.D.and Alan W. Langman, M.D.

Combined Mastoid/Middle

Cranial Fossa Repair of

Temporal Bone Encephalocele

Herniation of dura (meningocele) and/or brain(meningoencephalocele) into the mastoid or middle ear

has become uncommon, as the incidence of chronic oti-tis media, its intracranial complications, and surgery foreither condition has decreased. Prior to the modem an-

tibiotic era, herniation of intracranial contents occurredmostly in association with and following surgical treat-ment of otogenic intracranial abscesses, sigmoid sinusthrombophlebitis, and advanced temporal bone choles-teatoma. Since 1950, 177 cases of meningoceles andmeningoencephaloceles have been described. 1'2 Themajority of these cases have occurred following mas-

toidectomy.Failure to recognize the presence of either middle

ear or mastoid communication with either the middle3or posterior fossa4 can result in devastating sequellaesuch as meningitis, intracranial abscess hemorrhage, or

seizure. Even though improvements in the antibiotic

treatment of chronic otitis media have lessened the needfor surgical treatment of the mastoid cavity, meningo-celes and meningoencephaloceles still do occur. Therelatively rare modem-day occurrence adds to the diffi-culty in diagnosing these lesions at an early stage oftheir development. Despite improvements in radiologi-cal imaging of the temporal bone, delayed diagnosis ofbrain hemiation into the temporal bone continues to oc-

cur primarily due to the nonspecificity of clinical signsand symptoms. The following cases (all which had rela-tively large hemiations into the temporal bone) high-light this continuing problem.

RESU LTS

Six cases of large (>1 cm) temporal bone en-

cephalocele (TBE) of diverse etiology are described

185

Skull Base Surgery, Volume 8, Number 4, 1998 Tacoma Ear & Balance Clinic, Tacoma (C.R.S.) and Department of Otolaryngology, VirginiaMason Clinic, Seattle, Washington (A.W.L.). Reprint requests: Dr. Charles Souliere, Tacoma Ear & Balance Clinic, 915 Sixth Avenue, Suite 1,Tacoma, WA 98405. Copyright C 1998 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel.: +1 (212)760-0888. All rights reserved.

SKULL BASE SURGERY/VOLUME 8, NUMBER 4 1998

Table 1. Temporal Bone Encephalocele Patient Population-Clinical Course and OutcomePatients

Age/sexDefect

CSF leak

Etiology oftegmendefect

Time intervalbetweenetiology anddiagnosis (y)

Audio SRTpre/post

Reconstruction

Clinicalpresentation

Follow-upinterval/compl ications

40 y/male10.0 x12.0 mmIMCF

No

Temporalbonefractu re/traumatic

1

40 db/i5 db

CombinedMCF-Mastoid

Hearing loss,disequilibrium

1 8 months/none

2

41 y/male10.0 x12 mmMCF

Yes/recurrentmeningitis

Temporalbonefracture/traumatic

21

50 db/S db

Same as 1

Recurrentmeningitis,CSFrh norrhea,mastoidcholesteatoma

48 months/none

3

35 y/female15.0 x20.0 mmMCF

Yes

Prior mastoid-ectomy,age 9

3

4

48 y/female10.0 x

1 0.0 mmMCF

No

Chronicmastoiditis

10

5

36 y/male5.0 x

10.0 mmlateral MCF

No

Priormastoidectomy,age 23; revision,age 29

7

27db/27db 70db/70db 60db/40db

Same as 1 Same as 1 Transmastoid

Clearotorrhea,headache,fever

Recurrentotitis media,middle earmass-fluid

48 months/ 6 months/none temporary

expressiveaphasia

Hearing loss,middle ear extauditorycanal mass

2 y/none

6

55 y/female10.0 x

10.0 mmMCF

No

Chronicmastoiditis

20

1 0 db/1 0 db

Same as 1

Drainage,MastoidCholestea-toma

3 months/none

MCF, middle cranial fossa; CSF, cerebrospinal fluid.

within (Table 1). Two patients had suffered previoustemporal bone fracture, two had had prior mastoidec-tomy, and two patients demonstrated cholesteatomalchronic mastoiditis. Two patients (patients 2 and 4) hadundergone prior unsuccessful transmastoid repair. Clini-cal presentation was suggestive of TBE in only two in-

stances (patients 2 and 3). Nonspecific signs and symp-toms commonly associated with serous or chronic otitis(hearing loss, dysequilibrium, and middle ear fluid)were seen in the remaining four cases. Time intervalsfrom original etiology until diagnosis ranged from 1 to21 years. Patient 2 had undergone three previous mas-

Figure 1. Noncontrast coronal computed tomography scan of temporal bone. Note bony dehiscence in tegmen186 with encephalocele.

REPAIR OF TEMPORAL BONE ENCEPHALOCELE-SOULIERE AND LANGMAN

Figure 2. Combined middle cranial fossa-mastoidapproach for temporal bone encephalocele. Note herni-ated temporal lobe encephalocele.

toid procedures over a 21-year interval following trau-matic temporal bone fracture (Fig. 1).

The majority of patients were repaired through acombined mastoid-middle cranial fossa approach. Sur-gical approach was through an S-shaped post- andsupraauricular temporal incision. To provide maximalwould closure protection, an anteriorly based C-shapedtemporalis muscle flap complemented the posteriorlybased temporal skin flap. Craniotomy through the squa-mous temporal bone, amputation of herniated brain(Fig. 2), and complete visualization of the dural defectvia adequate temporal lobe retraction were performed(Fig. 3). Successful tegmen-dural repair was accom-plished extraduraly with autogenous fascia and bone(Fig. 4). Due to the limited and lateral dural defect pres-ent in case 5, transmastoid approach alone utilizing tra-gal cartilage and temporalis fascia was performed. Overfollow-up ranging from 3 months to 4 years, no evi-dence of reherniation or infection has been apparent. Al-though not the primary surgical goal, audiometric per-formance was often enhanced postoperatively.

Figure 3. Transmastoid amputation of encephalo-cele.

Figure 4. Temporalis fascia-calvarial bone graft re-pair placed via middle cranial fossa approach (blow-up ofcircled area, Fig. 3).

DISCUSSION

TBE has become less common as the incidence ofchronic mastoid infection and surgery for this conditionhas decreased. Due to declining incidence, the diagnosisof TBE may be delayed and may result in the develop-ment of serious complications such as cerebrospinalfluid (CSF) leak, meningitis, and epidural and subduralabscess. A high index of suspicion must be maintainedin evaluating patients with history of temporal bonetrauma or surgery to avoid potential misdiagnosis.

The clinical presentation of TBE can be dividedinto common and uncommon signs. Common signs ofTBE include CSF otorrhea or rhinorrhea, serous otitismedia, with or without hearing loss, recurrent meningi-tis, and a retrotympanic mass.2 Temporal lobe seizure,facial nerve paralysis, and expressive aphasia mayrarely be the presenting sign of TBE.5,6 The typical pre-sentation of TBE as a serous middle ear effusion or clearwatery otorrhea may be mistakenly attributed to morecommon mastoid-middle ear infections. In one recentstudy, 42% of patients with spontaneous CSF otorrheasecondary to tegmen-posterior fossa defects presentedwith otorrhea alone, whereas 33% had evidence of mid-dle ear effusion. Only 24% presented with classicalwarning signs such as meningitis.3 Definitive diagnosisis primarily based on laboratory and radiographic find-ings. In patients with suspected CSF otorrhea or rhinor-rhea, analysis for glucose, chloride, or I2 transferrin, aprotein found only in CSF, may be useful.6

Radiographic evaluation with high-resolution com-puted tomography (HRCT) and magnetic resonanceimaging (MRI) is the preferred means of diagnosis. 187

SKULL BASE SURGERY/VOLUME 8, NUMBER 4 1998

HRCT can demonstrate the location and size of bonydefects of the tegmen and posterior fossa and the pres-

ence of middle ear fluid-soft tissue. HRCT cannot,however, clearly distinguish between middle ear fluidand soft tissue. MRI, with its affinity for soft tissue def-inition, complements HRCT study in such patients. OnMRI study, cholesteotoma will appear isointense on T,weighting, and hyperintense on T2, whereas cholesterolgranuloma will appear hyperintense in both T, and T2.Brain herniation into the middle ear will appear isoin-tense on T /T2, will demonstrate continuity with in-tracranial contents, and will be nonenhancing. A classic"teardrop sign" distortion of temporal lobe gyri sec-

ondary to temporal lobe herniation may be observed.MRI study can also demonstrate dural integrity, al-though HRCT with intrathecal omnipaque (a low-osmo-larity, nonionic, water-soluble contrast agent) may benecessary to diagnose small CSF fistulous tracts.6

Numerous factors may contribute to the pathogen-esis of mastoid encephelocele. Congenital defects havebeen described in the mastoid tegmen of 21% of ca-

daver temporal bones studied; 6% demonstrated multi-ple sites of dehiscence.7 Bony dehiscence alone, whetherof the middle or posterior fossa, will not in of itself re-

sult in TBE. Dural injury, whether due to trauma, infec-tion, tumor, or surgery, is a necessary prerequisite.8 Fol-lowing dural injury, if the arachnoid layer remainsintact, a meningoencephelocele may result. If the arach-noid is also injured, herniation of the temporal lobeinto the mastoid (TBE) can occur. Loss of dural integ-rity following temporal bone fracture, tumor resection,or iatrogenic injury during mastoidectomy, with sub-sequent TBE development, is readily understood. Theetiology of apparent spontaneous dural defects of themiddle and posterior fossa34 is less well understood.Glasscock et a19 and Ferguson et al3 have proposed thatsmall elevations in baseline intracranial pressure, focalinflammation, or aging associated with congenital duralweakness may lead to spontaneous dural rupture. Gra-ham has observed that dural thickness in the temporallobe varies as a function of age and location and variesamong individuals.'0 Langman et al have further postu-lated that bone erosion secondary to prolonged contactwith arachnoid granulations can result in the loss of pos-terior fossa dural integrity.4

The surgical management of temporal lobe hernia-tion dates back historically to 1913, when Canfield de-scribed the closure of dural defect with fascial repair."Since that time, a number of reconstruction techniquesand materials of varying clinical complexity and loca-tion have been applied to the closure of TBE. In general,three separate issues must be addressed when one at-tempts surgical repair of a temporal bone encephecele:(1) management of brain herniation, (2) restoration ofdural integrity, and (3) exenteration of mastoid infectionand cholesteotoma.'0 The necessity of mastoid disease

188 eradication is well known to otologic surgeons and will

not be further addressed. Brain tissue herniated into themastoid is felt by most authors to be nonfunctional and,in general, should be excised. Glasscock et al have cau-tioned against reduction of herniated cerebral cortexdue to potential risk of temporal lobe aphasia or seizureactivity.9 Aristegui et al advocate amputation of herni-ated brain tissue via a middle cranial fossa approach,whereupon the amputated remnant is left undisturbed inthe mastoid as a further reinforcement against infec-tion. '

Restoration of dural integrity is of key importancein successful management of TBE. The size of en-cephalocele itself is not as important as that of the duraldefect.9 Dural defects as small as 2 mm can give rise toa TBE.3 Accurate dural closure and support of intracra-nial contents are imperative to prevent recurrence. Toaccomplish successful repair the surgeon has three pos-sible surgical options: (1) approach from below by atransmastoid technique, (2) combined approach by amiddle cranial fossa-mastoid technique, or (3) repairfrom above via middle cranial fossa approach alone. Inthe past, transmastoid approach alone was the procedureof choice for treatment of most mastoid encephalocele.Intracranial repair was reserved for large anteriomedialdefects.'2 In 1970, Dedo and Sooy described nine casesof ME that were managed via transmastoid approachonly. Herniated brain was amputated, and a temporalismuscle flap was rotated into the mastoid defect, fol-lowed by split thickness skin grafting with prolongedpacking of the cavity. Two of nine cases reherniated andrequired intracranial approach.'3 Similar high failurerates with transmastoid approach were noted by Fergu-son et a13 and were also seen in the original presentationof two cases in the current study. Due to the high risk ofrecurrence, transmastoid repair is now generally re-served for those cases with small, lateral effects withminimal dural defect. In general, such defects aresmaller than 1 cm2 and can be repaired with temporalisfascia alone. 1'3 Likewise, approach from above via MCFalone may be acceptable with small anteromedial de-fects in clean, previously unoperated ears.9 In larger de-fects (>1 cm2), combined approach via MCF-mastoidtechnique best permits meticulous eradication of mas-toid infection, accurate dural closure, and adequate sup-port of intracranial contents. The necessity of completeeradication of all mastoid infection from below is self-evident. Approach from above, utilizing dural and tem-poral lobe exposure with a middle fossa retractor, al-lows meticulous placement of the graft material withsupport of intracranial contents verified visually. Auto-genous graft material is preferred, and successful repairhas been described with composite perichondrial-auric-ular cartilage graft,3'18 septal cartilage wrapped withtemporalis fascia,' and cranial bone sandwiched withtemporalis fascia.10'4 Both extra- and intradural graftplacement have been described. Either approach ap-pears acceptable. 9 Finally, Aristegui et al have recently

REPAIR OF TEMPORAL BONE ENCEPHALOCELE-SOULIERE AND LANGMAN

described a two-staged approach in those cases withlarge anterior tegmen defects and active middle ear in-fection. These authors reported meningitis in 6 of 27cases initially treated with simultaneous combinedMCF-mastoid approach. To lessen this risk the authorsrevised their approach in later cases. Initial MCF ap-proach alone with extradural defect reconstruction andbrain amputation into the mastoid cavity was performedas a first stage. Three to 6 months later, second-stagemastoidectomy was performed. Utilizing this staged ap-proach, the incidence of postoperative meningitis de-clined to 4%.1

CONCLUSION

The diagnosis, evaluation, and surgical treatmentof TBE are detailed within. Due to the nonspecificity ofusual clinical signs, delay in diagnosis is common andmay result in significant morbidity. Any patient withpersistent unilateral serous otitis media, clear otorhinor-rhea, or middle ear mass must be evaluated for possibleTBE. Patients with history of temporal bone trauma,prior mastoidectomy, or meningitis are particularly sus-pect. Definitive diagnosis can best be established bycombined HRCT and MRI radiographic study. Middleear effusion or otorrhea should be tested for the pres-ence of I2 transferrin. Transmastoid repair may be suit-able in isolated small lateral dural defects. Wide intra-operative exposure, accurate dural closure, and supportof intracranial contents with autologous bone-cartilageare imperative to prevent recurrence. We find that per-manent repair can best be performed with a combinedtemporal bone-middle cranial fossa approach.

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