extended middle fossa approach to lateralized pontine

CLINICAL ARTICLEJ Neurosurg Pediatr 21:384–388, 2018

Cavernous malformations (cavernomas) occur in up to 0.5% of the population, with nearly one-quarter of these lesions found in the posterior fossa, most

commonly the pons.14 Hemorrhage of pontine cavernomas can result in significant morbidity and mortality, and some authors advocate resection of symptomatic brainstem cav-

ernomas after the first hemorrhage.14,15 Nonetheless, surgi-cal approaches to brainstem cavernomas must be carefully planned and executed due to the complex extra- and intra-dural anatomy of this region.

The technically demanding extradural subtemporal extended middle fossa “rhomboid” approach relies on

ABBREVIATIONS AE = arcuate eminence; CN = cranial nerve; CPA = cerebellopontine angle; GSPN = greater superficial petrosal nerve; V3 = mandibular branch of the trigeminal nerve.SUBMITTED July 10, 2017. ACCEPTED October 31, 2017.INCLUDE WHEN CITING Published online February 2, 2018; DOI: 10.3171/2017.10.PEDS17381.

Extended middle fossa approach to lateralized pontine cavernomas in childrenRobert C. Rennert, MD,1 Reid Hoshide, MD,1 Mark Calayag, MD,1 Joanna Kemp, MD,1 David D. Gonda, MD,1 Hal S. Meltzer, MD,1 Takanori Fukushima, MD,2 John D. Day, MD,3 and Michael L. Levy, MD, PhD1

1Department of Pediatric Neurosurgery, University of California, San Diego, California; 2Carolina Neuroscience Institute, Raleigh, North Carolina; and 3Department of Neurosurgery, University of Arkansas, Little Rock, Arkansas

OBJECTIVE Treatment of hemorrhagic cavernous malformations within the lateral pontine region demands meticulous surgical planning and execution to maximize resection while minimizing morbidity. The authors report a single institu-tion’s experience using the extended middle fossa rhomboid approach for the safe resection of hemorrhagic cavernomas involving the lateral pons.METHODS A retrospective chart review was performed to identify and review the surgical outcomes of patients who un-derwent an extended middle fossa rhomboid approach for the resection of hemorrhagic cavernomas involving the lateral pons during a 10-year period at Rady Children’s Hospital of San Diego. Surgical landmarks for this extradural approach were based on the Fukushima dual-fan model, which defines the rhomboid based on the following anatomical structures: 1) the junction of the greater superficial petrosal nerve (GSPN) and mandibular branch of the trigeminal nerve; 2) the lat-eral edge of the porus trigeminus; 3) the intersection of the petrous ridge and arcuate eminence; and 4) the intersection of the GSPN, geniculate ganglion, and arcuate eminence. The boundaries of maximal bony removal for this approach are the clivus inferiorly below the inferior petrosal sinus; unroofing of the internal auditory canal posteriorly; skeletonizing the geniculate ganglion, GSPN, and internal carotid artery laterally; and drilling under the Gasserian ganglion anteriorly. This extradural petrosectomy allowed for an approach to all lesions from an area posterolateral to the basilar artery near its junction with cranial nerve (CN) VI, superior to the anterior inferior cerebellar artery and lateral to the origin of CN V. Retraction of the mandibular branch of the trigeminal nerve during this approach allowed avoidance of the region involv-ing CN IV and the superior cerebellar artery.RESULTS Eight pediatric patients (4 girls and 4 boys, mean age of 13.2 ± 4.6 years) with hemorrhagic cavernomas involving the lateral pons and extension to the pial surface were treated using the surgical approach described above. Seven cavernomas were completely resected. In the eighth patient, a second peripheral lesion was not resected with the primary lesion. One patient had a transient CN VI palsy, and 2 patients had transient trigeminal hypesthesia/dysesthesia. One patient experienced a CSF leak that was successfully treated by oversewing the wound.CONCLUSIONS The extended middle fossa approach can be used for resection of lateral pontine hemorrhagic caver-nomas with minimal morbidity in the pediatric population.https://thejns.org/doi/abs/10.3171/2017.10.PEDS17381KEY WORDS pontine cavernoma; extended middle fossa approach; rhomboid; surgical technique

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an anterior petrosectomy to gain surgical access to the petroclival and medial cerebellopontine angle (CPA) re-gions.6,12 This approach provides exposure to the antero-lateral brainstem between the level of cranial nerve (CN) V and the CN VII–VIII complex, with tolerated levels of temporal lobe retraction and no transposition of nerves or vessels.12 The rhomboid technique is thus well suited for surgical resection of lateralized pontine cavernomas. Although other complex skull base approaches have been used in children,3,11,18 reports of this approach in the pe-diatric population are limited.11 We report a single in-stitution’s experience using the extended middle fossa rhomboid approach for the safe resection of hemorrhagic cavernomas involving the lateral pons.

MethodsPatient Population

Based on a single surgeon’s case logs, a retrospective chart review was performed to identify and review the sur-gical outcome of any patient who underwent an extended middle fossa rhomboid approach for a hemorrhagic caver-noma involving the lateral pons during a 10-year period at

Rady Children’s Hospital of San Diego. Surgery for cav-ernoma resection and hematoma evacuation was pursued only in patients with symptomatic hemorrhages and with extension of the hemorrhage to the pial surface. The fol-lowing data were collected: age, sex, location of lesion, operative details, CN injuries, and perioperative compli-cations. Patient consent for procedures, data collection, and review was obtained based on institutional guidelines and in accordance with Health Insurance Portability and Accountability Act regulations. All procedures were per-formed by the senior author of this manuscript (M.L.L.).

Surgical ApproachAll surgeries were performed with intraoperative neu-

ronavigation and neuromonitoring. Lumbar drains for pro-phylactic CSF diversion were not routinely used. Patients were positioned supine, with the head turned away from the side chosen for the approach. A curvilinear incision from anterior to the tragus at the level of the zygoma in-feriorly to just below the superior temporal line superiorly was made (Fig. 1A). The temporalis was split and a tem-poral craniotomy was performed using a high-speed drill,

FIG. 1. Surgical technique for extended middle fossa approach. A: A temporal craniotomy is performed via a curvilinear incision from the zygoma inferiorly to just below the superior temporal line superiorly. B: The temporal dura is elevated from the floor of the temporal fossa to identify the landmarks for the extended middle fossa approach: 1) the junction of the GSPN and V3; 2) the lateral edge of the porus trigeminus; 3) the intersection of the petrous ridge and AE; and 4) the intersection of the GSPN, genicu-late ganglion, and AE. An anterior petrosectomy is then performed by drilling from the internal auditory canal posteriorly to under the Gasserian ganglion anteriorly; skeletonizing the geniculate ganglion, GSPN, and internal carotid artery laterally; and drilling the clivus inferiorly below the inferior petrosal sinus. FS = foramen spinosum. C: The dura is then opened sharply (dotted lines), and the superior petrosal sinus is transected to increase exposure. From Diaz Day J: The middle fossa approach and extended middle fossa approach: technique and operative nuances. Neurosurgery 70(2 Suppl Operative):192–201, 2012. Copyright Oxford University Press. Published with permission. Figure is available in color online only.



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ensuring that the inferior aspect of the craniotomy was flush with the floor of the temporal fossa. The temporal lobe dura mater was elevated from the floor of the tempo-ral fossa to identify the critical surgical landmarks for the extended middle fossa approach.

Surgical landmarks for the extended middle fossa ap-proach were based on the Fukushima dual-fan model, which defines the rhomboid based on the following ana-tomical structures: 1) the junction of the greater superfi-cial petrosal nerve (GSPN) and mandibular branch of the trigeminal nerve (V3); 2) the lateral edge of the porus tri-geminus; 3) the intersection of the petrous ridge and arcu-ate eminence (AE); and 4) the intersection of the GSPN, geniculate ganglion, and AE (Fig. 1B). The boundaries of maximal bony removal for this approach, performed with a diamond burr on a high-speed drill and suction irriga-tion, are the clivus inferiorly below the inferior petrosal sinus; unroofing of the internal auditory canal posteriorly; skeletonizing the geniculate ganglion, GSPN, and internal carotid artery laterally; and drilling under the Gasserian ganglion anteriorly. The internal auditory canal was local-ized and unroofed using the House technique, wherein the

GSPN is followed to the geniculate ganglion, the labyrin-thine segment of the facial nerve, and ultimately the fun-dus of the canal.9 This extradural petrosectomy allowed for an approach to all lesions from an area posterolateral to the basilar artery near its junction with CN VI, superior to the anterior inferior cerebellar artery, and lateral to the origin of CN V. Retraction of V3 during this approach al-lowed avoidance of the region involving CN IV and the superior cerebellar artery.

Following this extradural dissection, the dura was then opened sharply, and the superior petrosal sinus was tran-sected to increase prepontine exposure (Fig. 1C). The cav-ernomas were then localized, dissected from surrounding brain parenchyma, and removed piecemeal. Cavernoma location within the pons was described using a zone sys-tem based on the distance of the cavernoma to the brain-stem exit site of CN V (zone I, closest; zone II, intermedi-ate; and zone III, most distal/lateral) (Fig. 2). Following resection, dural defects were closed using vascularized pericranium and/or abdominal fat grafts. The temporal craniotomy bone flap was secured in place, and the galea and skin were closed. Patients were taken to the pediatric intensive care unit for early care and recovery.

ResultsEight pediatric patients (4 girls and 4 boys, mean age

13.2 ± 4.6 years) were identified with hemorrhagic caver-nomas involving the lateral pons that were resected using an extended middle fossa approach (Table 1; Fig. 3). Five lesions were lateralized to the left and 3 to the right. One lesion was in zone I within the pons, 4 lesions were in zone II, and 3 lesions were in zone III. In 7 of the 8 patients, the cavernomas were completely resected, whereas in the eighth patient, a second peripheral lesion was not resected with the primary cavernoma.

Regarding complications, 1 patient had a transient CN VI palsy, and 2 patients had transient trigeminal hypesthe-sia/dysesthesia. One patient experienced a CSF leak that was successfully treated by oversewing the wound.

DiscussionThe extradural subtemporal extended middle fossa

rhomboid approach provides a wide operative corridor for the treatment of lateralized pontine hemorrhagic caver-

FIG. 2. Zones of pontine cavernomas. Lateral pontine cavernoma loca-tions were recorded using a zone system based on the relationship of the cavernoma to the brainstem exit site of CN V (zone I, closest; zone II, intermediate; and zone III, most distal/lateral). MMA = middle meningeal artery; V1 = ophthalmic branch of the trigeminal nerve; V2 = maxillary branch of the trigeminal nerve. Image courtesy of Mauro A. T. Ferreira, Barrow Neurological Institute, Phoenix, AZ. Published with permission. Figure is available in color online only.

TABLE 1. Patient demographic data and surgical results

Pt No. Age (yrs) Sex Side Zone CN Injury CN Injury Resolution Other Complications Complete Resection

1 8 M Lt I VI Yes NA No*2 10 M Rt II V Yes NA Yes3 5 M Lt II V Yes NA Yes4 14 F Lt II NA NA CSF leak Yes5 16 F Lt II NA NA NA Yes6 16 F Lt III NA NA NA Yes7 17 F Rt III NA NA NA Yes8 18 M Rt III NA NA NA Yes

NA = not applicable; Pt = patient.* Satellite lesion left.


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nomas. This extended approach, which differs from the standard middle fossa approach used only to access the internal auditory canal from above, gives surgical access to the upper CPA and clival regions via removal of the anterior aspect of the petrous ridge. Following this extra-dural work, the dura is opened subtemporally to allow for visualization and transection of the tentorium and for ac-cess to the superior anterolateral posterior fossa. For fur-ther visualization of this anatomical region, the superior petrosal sinus can be transected.

Although not needed in this patient series because the surgical target was the lateral pons, this versatile approach can also be combined with transmastoid-retrolabyrinthine drilling as part of a combined petrosal technique, and ex-tends surgical access to the inferior CPA and the lateral pontomedullary region down to approximately the CN IX–X complex. This combined approach is nonetheless typically reserved for large lesions of the CPA that involve the CNs, where visualization of the contralateral side and ventral brainstem, as well as preservation of hearing, are surgical goals.4

Although not used in this series, the far lateral and standard suboccipital approaches are other techniques that can be considered for the resection of hemorrhagic brain-stem cavernomas.1 Specifically, the far lateral approach (termed the “complete far lateral approach” with all bony removal) combines a partial C-1 laminectomy and suboc-cipital craniotomy with drilling of the occipital condyle and jugular tubercle, but is primarily used to access the lower clival and ventral foramen magnum regions.16 In

contrast, the retrosigmoid approach provides a direct cor-ridor to the lateral pons and CPA, and other authors have described resection of similarly located lateral pontine cavernomas using this approach.1 In the senior author’s experience, however, the largely parallel trajectory of the suboccipital approach in relation to the pons, as well as the high density of critical neurovascular structures one must traverse with this approach, is suboptimal compared with the orthogonal trajectory and clear surgical window provided by the extended middle fossa technique for later-alized pontine lesions.

Although well described in the adult population, the extended middle fossa approach is sparingly used in pe-diatric patients due to the relative rarity of lesions in this area and apparent predilection for alternative surgical ap-proaches among pediatric neurosurgeons.1,5,8,13,19 In one of the few reports on the subject, a multiinstitutional series of 13 patients accumulated over an undefined time period, the authors describe the use of the extended middle fossa approach (combined with a posterior petrosal approach) in two 19-year-old patients for a petroclival meningioma and a lateral pontine cavernoma, respectively.11 Similarly, in a single institution’s review of 26 pediatric skull base sur-geries performed over a 10-year period, only 1 patient was treated with an extended middle fossa approach (called extended transpetrosal in this work) for a schwannoma.17 To the authors’ knowledge, the data set presented herein is thus the largest series of extended middle fossa approach-es for any pathology in a pediatric population.

When adapting the extended middle fossa technique to

FIG. 3. Patient 8. Representative MR images obtained in an 18-year-old male with a history of familial cavernous malformations who presented with a progressive right-sided CN IV palsy. MRI demonstrated serial hemorrhages into the right posterior lateral pontine region, with local mass effect and edema. Surgery was scheduled at this time. A: Serial (i–iii) axial T2-weighted FLAIR images. B: Sagittal T1-weighted image. C: Coronal gradient echo image.



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the pediatric population, there are fewer unique anatomi-cal considerations than with other skull base approaches. For example, in anterior skull base surgery, surgeons must be aware of the relatively anterior displacement of the pterion in the pediatric versus adult populations to avoid entering the periorbita with a keyhole burr hole, a less prominent sphenoid wing, and the possibility of mini-mally or unaerated frontal sinuses. In the posterior skull base, relative differences in the size and aeration of the mastoid region, which can affect the distance between the sigmoid sinus and the labyrinth, are similarly important considerations.8,11 For the extended middle fossa approach, however, the key anatomical landmarks for this technique remain in place despite their reduced size in the pediatric population.

Our surgical results are in line with previous reports in the adult population demonstrating generally favor-able outcomes for the resection of brainstem caverno-mas.2,7,10,14,15 The major complication risks with the ex-tended middle fossa approach and subsequent intrapontine cavernoma resection include CN, brainstem, and vascular injuries, as well as CSF leak. Neurophysiological monitor-ing of CNs, somatosensory evoked potentials, and motor evoked potentials is critical to reduce the surgical risks to involved CNs and major motor and sensory tracts.

To minimize disruption of normal pontine tissue dur-ing cavernoma resection, it is the senior author’s practice to only use this approach for lesions with hemorrhages that extend to the pial surface. Intraoperatively, the sur-rounding hematoma is removed first, followed by a me-ticulous dissection around the periphery of the lesion. Sur-rounding hemosiderin-stained gliotic tissue should not be removed.14 CSF leaks are best avoided with a meticulous multilayered closure, including a watertight dural seal, al-logeneic dural graft, and pericranial flaps as needed. It is the authors’ recommendation that this approach only be attempted by experienced skull base surgeons with intri-cate anatomical knowledge of all involved areas.

ConclusionsWith appropriate planning and skull base knowledge,

the extended middle fossa approach can be used to access the superior CPA for resection of lateral pontine hemor-rhagic cavernomas with minimal morbidity in pediatric patients.

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Bristol R, et al: Cavernous malformations of the brainstem presenting in childhood: surgical experience in 40 patients. Neurosurgery 67:1589–1599, 2010

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16. Spektor S, Anderson GJ, McMenomey SO, Horgan MA, Kel-logg JX, Delashaw JB Jr: Quantitative description of the far-lateral transcondylar transtubercular approach to the foramen magnum and clivus. J Neurosurg 92:824–831, 2000

17. Teo C, Dornhoffer J, Hanna E, Bower C: Application of skull base techniques to pediatric neurosurgery. Childs Nerv Syst 15:103–109, 1999

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DisclosuresThe authors report no conflict of interest concerning the materi-als or methods used in this study or the findings specified in this paper.

Author ContributionsConception and design: Levy, Rennert, Hoshide. Acquisition of data: Levy, Calayag, Kemp. Analysis and interpretation of data: Levy, Hoshide, Calayag, Kemp, Gonda. Drafting the article: Levy, Rennert, Hoshide, Calayag, Kemp, Gonda, Meltzer, Day. Criti-cally revising the article: all authors. Reviewed submitted version of manuscript: Levy, Rennert, Fukushima.

CorrespondenceMichael L. Levy: University of California, San Diego, CA. [email protected].


extended middle fossa approach to lateralized pontine

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