Transmastoid Trautman's Triangle Combined Low Retrosigmoid Approach for Foramen Magnum Meningiomas: Surgical Anatomy and Technical Note

Abstract

Objective  This study was aimed to assess the potential of utilizing a transmastoid Trautman's triangle combined low retrosigmoid approach for ventral and ventrolateral foramen magnum meningiomas (FMMs) surgical treatment.

Methods  We simulated this transmastoid Trautman's triangle combined low retrosigmoid approach using five adult cadaveric heads to explore the associated anatomy in a step-by-step fashion, taking pictures of key positions as appropriate. We then employed this approach in a single overweight patient with a short neck who was suffering from large ventral FMMs and cerebellar tonsillar herniation.

Results  Through cadaver studies, we were able to confirm that this transmastoid Trautman's triangle combined with low retrosigmoid approach achieves satisfactory cranial nerve and vasculature visualization while also offering a wide view of the whole of the ventrolateral medulla oblongata. We, additionally, have successfully employed this approach to treat a single patient suffering from large ventral FMMs with cerebellar tonsillar herniation.

Conclusion  This transmastoid Trautman's triangle combined low retrosigmoid approach may represent a complement to treatment strategies for ventral and ventrolateral FMMs, particularly in patients with the potential for limited surgical positioning due to their being overweight, having a short neck and suffering from cerebellar tonsillar herniation.

Introduction

Foramen magnum meningiomas (FMMs) account between 1.8 and 3.2% of intracranial meningiomas. ^{1 2} As described previously, ³ FFMs arise anteriorly from the inferior third of the clivus to the upper edge of the C ₂ body, laterally from the jugular tubercle to the C ₂ laminae, and posteriorly from the anterior border of the occipital squama to the C ₂ spinous process. FMMs are benign tumors that grow in a slow and indolent fashion, which typically results in their being very large when first detected clinically. ⁴ In patients with symptomatic FMMs who are otherwise in good condition, surgical removal remains the primary treatment strategy, but such surgeries can be challenging owing to the close positioning of FMMs relative to key neurovascular structures. ^{2 5 6} An ideal surgical approach in this region is thus one that not only achieves effective tumor resection, but also reduces the risk of surgical injury to the patient and ensures a satisfactory postoperative prognosis. At present, the ideal surgical approaches for treating ventral and ventrolateral FMMs remains controversial. ^{6 7}

Several factors can influence the ideal surgical approach in a given patient, including the size and position of a tumor, patient age, and overall condition, and the extent to which this tumor is compressing proximal neural structures. ⁸ These complexities have led to the publication of a range of different surgical approaches for treating FMMs, including the conventional posterior midline approach, ^{9 10 11} transoral or transnasal anterior approaches, ^{2 12} and far-lateral or extreme-lateral approaches. ^{5 13} Individually, each of these approaches offers specific advantages and disadvantages. The conventional midline approach is typically familiar to surgeons, offering an easy, rapid, and safe means of accessing the affected region, making this approach ideal for dorsal or dorsolateral FMMs. ^{11 14 15} In the case of ventral and ventrolateral FMMs, however, this approach is primarily used only for the treatment of selected large tumors that can undergo surgical debulking, thereby allowing for sufficient space for dissecting surrounding neurovascular structures. ^{9 10 14} As this approach does not entail a lateral extension of the craniotomy, there is initially relatively limited exposure, meaning that the site of dural origin can only be manipulated following tumor removal. As such, for highly vascularized tumors, extreme caution must be taken when employing this approach. ¹⁶ When resecting extradural or ventrally located FMMs, anterior approaches are frequently employed as they offer direct access to the lesion without the need for substantial neurovascular manipulation. ^{2 17} However, such approaches are associated with several risks including meningitis, leakage of cerebrospinal fluid, craniocervical instability, and velopalatine insufficiency. ^{11 18} This has led some researchers to propose that the complications far outweigh the benefit. ¹¹ Perhaps more pertinently, FMMs that are restricted to regions ventral to the brainstem are not common, with lateral extensions of such tumors being fairly common. As a consequence, lateral approaches have been popularized for the removal of such tumors, as they allow surgeons to view the region anterior to the neuraxis, eliminating the need for neuraxis handling and displacement. ⁸ These far-lateral or extreme-lateral approaches, however, can be very technically challenging to implement, with many surgeons not being experienced with such approaches. In addition, lateral bony exposures can result in an associated increase in the risk of injury to the vertebral artery and lower cranial nerves, and some amount of occipital condyle drilling is generally needed to ensure an optimal surgical corridor, potentially resulting in occipitocervical junction instability and requiring eventual occipitocervical fusion. ^{19 20}

These past findings clearly demonstrate that it is vital to tailor surgical procedures for FMMs removal to individual case requirements. In the present study, we sought to explore the transmastoid Trautman's triangle combined low retrosigmoid approach to FMMs removal and to discuss the rationale behind this approach and its associated indications.

Materials and Methods

Anatomic Study

The Institutional Review Board of the Wannan Medical College, Wuhu, China, approved this study. We obtained a total of five freshly prepared adult cadaveric heads that had been formaldehyde fixed and injected using colored silicone. Using these heads, we conducted a simulated transmastoid Trautman's triangle combined low retrosigmoid approach, allowing us to explore the anatomical aspects for this procedure in a stepwise manner such that we were able to reliably determine which muscles, bones, and neurovascular structures were involved.

Clinical Case

We eventually applied this technique in a single patient who was overweight, had a short neck, and suffering from a large ventral FMM and cerebellar tonsillar herniation. The surgical and clinical data from this patient were subjected to retrospective review.

Anatomic Considerations

Skin Incision

A horseshoe flap was used for exposure of the region of interest, given that such a flap offers better visualization of the layers of musculature and their association with proximal neurovascular structures. This incision was made with the upper limb at 2 cm above the auricle, the posterior limb in the midline, and the inferior incision at the level of the C ₃ –C ₄ vertebrae. The lateral limb descended from just behind the ear to 4 cm below the mastoid tip.

Suboccipital Soft-Tissue Structures

In previous reports, we have offered comprehensive descriptions of suboccipital soft-tissue structures such as the nuchal muscles, occipital artery (OA), and the third vertebral artery segment. ²¹ In brief, there are three primary muscular planes within the nuchal region. After the flap is opened, a superficial layer containing the trapezius and sternocleidomastoid muscle are exposed ( Fig. 1A ). There is an intersection between the OA and the greater occipital nerve (GON) at the sternocleidomastoid muscle attachment medial edge. The mid layer of musculature contains the splenius capitis, longissimus capitis, and semispinalis capitis ( Fig. 1B and C ), with the OA proceeding deep within the splenius capitis and the GON piercing the trapezius. After removal of the splenius capitis, the longissimus capitis muscles are exposed, with the OA crossing the muscle either on or just below its surface. The deepest layer of musculature in this region contains the superior and inferior oblique muscles, and the major and minor rectus capitis posterior muscles ( Fig. 1D ). The OA exhibited a lateral progression in this region, rising between the digastric posterior belly and the rectus capitis lateralis and proceeding up the digastric posterior belly and the superior oblique muscle ( Fig. 1D ). The major rectus capitis posterior muscle serves as a medial and superior boundary for this region, while the superior oblique bounds this region laterally and superiorly, and the inferior oblique bounds this region laterally and inferiorly, forming the suboccipital triangle ( Fig. 1D ). The horizontal portion of vertebral artery and the C ₁ nerve are deep in the suboccipital triangle, lying on the upper surface of vertebral artery groove ( Fig. 1E ). It is vital that surgeons exercise caution at this stage to prevent injury to vertebral artery, as it may exhibit an unusual course or present with loops within this suboccipital region ( Fig. 1F ).

Fig. 1.

Simulation of the transmastoid Trautman's triangle combined low retrosigmoid approach. ( A ) The flap was opened, exposing the superficial trapezius and sternocleidomastoid muscles, with the OA and GON intersecting at the medial edge of the sternocleidomastoid muscle attachment. ( B and C ) The splenius capitis, longissimus capitis, and the semispinalis capitis muscles form the middle layer of musculature, with the OA running deep into the splenius capitis and the GON piercing the trapezius muscle ( B ). Splenius capitis removal allows for exposure of the longissimus capitis muscles, with the OA being visible crossing under the surface of the longissimus capitis ( C ). ( D ) the deep layer of musculature is composed of the superior and inferior oblique muscles, and the major and minor rectus capitis posterior muscles, with lateral progression of the OA such that it rises between the digastric posterior belly and the rectus capitis lateralis, proceeding up the digastric posterior belly and the superior oblique muscle. ( E ) The deep layer of muscles was fully removed, allowing for full V3 segment exposure on the upper surface of vertebral artery groove. ( F ) In some cases, the V3 segment can become elongated and tortuous, looping backward with posterior bulging between the suboccipital triangle lips. A, artery; Cap, capitis; GON, greater occipital nerve; Inf., inferior; Lev, levator; Long., longissimus; Maj., major; M., muscle; OA, occipital artery; Obl., oblique; Post., posterior; Rec., rectus; Scap, scapula. Semispin., semispinalis; Splen, splenius; Sup., superior; Vert., vertebral.

Transmastoid Trautman's Triangle Craniectomy

Bone Work

We first identified bony markers of the temporal bone and surrounding surfaces, including the anterior external auditory meatus, the spine of Henley, the suprameatal triangle, the supramastoid crest (temporal line), the asterion, and the mastoid tip ( Fig. 2A ). These anatomical markers are of value when conducting a mastoidectomy, which is initiated via usage of a high-speed burr for resection of the mastoid triangle outer cortex ( Fig. 2B ). The inferior temporal line serves as a superior boundary for the mastoid triangle, whereas the posterior ear canal and the mastoid tip superficial to the digastric groove for them anterior and posterior boundaries, respectively. We then removed bone from the posterior margin of sigmoid sinus at the same depth until clear delineation of the sigmoid sinus was achieved ( Fig. 2C ). A diamond burr was next used to grind along the sigmoid sinus to the jugular bulb, leaving only a thin shell of bone cortex on its surface that can then later be elevated with a freer elevator. Next, the mastoid air cells were removed forward and upward, exposing the middle cranial fossa base and associated dura mater. Proximal mastoid air cells were then further ground forward to expose the bony labyrinth. After this drilling is complete, the antrum, which is a large air cell located superficially to the bony labyrinth and leading into the middle ear, should be visible deep inside of the supremeatal triangle posterior to the posterior ear canal and the spine of Henle ( Fig. 2D ). The incus is the first structure of the middle ear encountered during this approach, being located deep and anterior relative to the antrum with its short process pointing to the facial nerve, serving as a valuable anatomical marker for its location ( Fig. 2E and Supplementary Fig. S1A ; available online only). After entering the antrum, it is possible to identify the lateral semicircular canal lying deep thereto, with the fallopian canal running between 1 and 2 mm in front of this canal, thus allowing the lateral semicircular canal prominence to be a key anatomical marker for facial nerve localization. Next, attention must be paid to the digastric ridge at the inferior portion of the mastoid at the mastoid tip, with the facial nerve being located in the fallopian canal anterior to this ridge ( Fig. 2E ). Using these three anatomical markers, it is thus possible to reliably locate and determine the course of the mastoid segment of the facial nerve ( Fig. 2E ). After the nerve course has been established, it is possible to safely resect posterior facial nerve air cells and to trace the jugular bulb along the sigmoid sinus. Through anterior drilling from the sinodural angle along the middle fossa, the superior semicircular canal, which lies perpendicular to the lateral semicircular canal, is exposed. The point where the posterior semicircular canal is bisected by the lateral semicircular canal can be used for its location. The exposure of Trautman's triangle is then increased via maximizing the posterior bone of the posterior semicircular canal, allowing Trautman's triangle to be reliably identified as the region with the sigmoid as a posterior border, the posterior semicircular canal as an anterior border, and the superior petrosal sinus as a superior border ( Fig. 2E and Supplementary Fig. S1A ; available online only).

Fig. 2.

Transmastoid Trautman's triangle craniectomy. ( A ) Bony marker identification o on the right lateral temporal bone. ( B ) Mastoidectomy is initiated via use of a high-speed burr for resection of the outer cortex of the mastoid triangle, which is superiorly bounded by the inferior temporal line, posteriorly by the mastoid tip superficial to the digastric groove, and anteriorly by the posterior ear canal. ( C ) Next, mastoid air cells are entered, with bone being removed from the posterior margin of the sigmoid sinus at the same depth until full delineation of the sigmoid sinus was achieved. ( D ) Following superficial air cell drilling to expose the opening into the antrum and the prominence of lateral semicircular canal on the medial wall of the antrum, mastoidectomy was conducted. ( E ) After completing the mastoidectomy, the semicircular canals and Trautman's triangle are evident, with the latter being bounded by the sigmoid, superior petrosal sinus, and posterior semicircular canal. ( F ) Following dura mater opening, slight backward retraction of the sigmoid sinus was conducted, exposing the CN V–X and ventrolateral upper medulla oblongata. Ac, auditory; CN, cranial nerve; Ext, external; Jug, jugular; Lat, lateral; Pet, petrosal; Post, posterior; Semicirc, semicircular; Sig, sigmoid; Sp, spine; Sup, superior; Supramast, supramastoid.

Dural Opening

The dura mater was cut to the superior jugular bulb 1 to 2 mm parallel to the inferior margin of the superior petrosal sinus and the anterior margin of sigmoid sinus. Next, the dura matter was pulled forward, thereby exposing the inner structures within Trautman's triangle. When the sigmoid sinus was slightly retracted backward, the cranial nerve (CN) V–X and the ventrolateral upper medulla oblongata were thereby exposed ( Fig. 2F and Supplementary Fig. S1B ; available online only).

Low Retromastoid Craniectomy

Bone Removal

The upper craniectomy border is generated from the inferior margin of transverse sinus, inferiorly including the foramen magnum, medially to the midline, and extending as far laterally as possible. The occipital condyle was not resected ( Fig. 3A ).

Fig. 3.

Low retromastoid craniectomy. ( A ) A craniotomy is performed superiorly at the level of the inferior margin of the transverse sinus, inferiorly including the foramen magnum, medially to the midline and extending laterally as far as possible. ( B ) Following dura opening and gentle cerebellar retraction, CN V–XII and ventrolateral medulla oblongata exposure is achieved. A, artery; Jug, jugular; OC, occipital condyle; Pet, petrosal; Semicirc, semicircular; Sig, sigmoid; Sup, superior; Tran, transverse; Vert., vertebral.

Dural Opening

A curvilinear incision is used to open the dura, proceeding medially along the transverse and sigmoid sinus, leaving several millimeters between the incision and the sinus to allow for eventual closure. A total of 34 tack-up sutures were then placed as the surgical view increased, reducing the need for cerebellar retraction as much as possible. With the dura opened, CN V–XII and entire ventrolateral medulla oblongata were exposed after gentle retraction of cerebellum ( Fig. 3B ).

Surgical Considerations

Patient Positioning and Skin Incision

A 62-year-old woman suffered from a headache for 6 months and presented with dysdipsia, dysphagia, and walking unstable for 3 months. To minimize compression of the brainstem and surrounding neurovasculature through excess neck rotation or flexion, the patient was treated while in the left lateral position with slight head flexion and rotation toward the ground in a Mayfield's fixation apparatus. An opisthotic C -shaped incision was created beginning from the level of the upper portion of the ear pinna and descending downward 2-fingerbreadths medially and behind the mastoid tip, and extending to skin crease in the upper neck 4 cm under the mastoid tip ( Fig. 4A ).

Fig. 4.

An overview of the transmastoid Trautman's triangle combined low retrosigmoid approach. ( A ) The opisthotic C -shaped incision employed for this approach. ( B ) Following suboccipital craniotomy, a high speed burr was used to conduct osteotomy of the mastoid cortex, with a chisel used for undersurface detachment. ( C ) Cerebellopontine angle cistern CSF was released to reduce intracranial pressure, which was then further reduced via removal of portions of the tumors and its basement. ( D ) Remaining tumors were removed via the low retrosigmoid approach. CSF, cerebrospinal fluid; Sig, sigmoid.

Right Transmastoid Trautman's Triangle Combined Low Retrosigmoid Craniectomy

After anterolaterally retracting the skin/muscle flap over the auricle, one burr hole is created under the transverse-sigmoid junction located just medially and inferiorly relative to the asterion. Next, a craniotomy is performed superiorly at the level of the burr hole to expose the medial edge of the sigmoid sinus and expose the posterior rim of the foramen magnum inferiorly. Following removal of the suboccipital craniotomy flap, exposure of the mastoid lateral edge is achieved, and a neurodissector can then be used to separate the mastoid process from the sigmoid sinus. To continue the mastoidectomy, a high speed burr is used to perform osteotomy of the mastoid cortex along the inferior temporal line, which is superior to this flap, and the mastoid tip superficial to the digastric groove, which is posterior to this flap. A chisel is then used to detach the undersurface ( Fig. 4B ). Next, a mastoid cortex flap is prepared to facilitate reconstruction, and mastoid air cells are continuously ground until Trautman's triangle exposure is achieved.

Tumor Resection and Closure

After first opening the dura mater at the Trautman's triangle, intracranial pressure is reduced via releasing the cerebrospinal fluid (CSF) within the cerebellopontine angle cistern and by partially removing the basement and upper portions of the tumor ( Fig. 4C ). Next, opening of the retrosigmoid dura mater was conducted, allowing for removal of the herniated right cerebellar tonsil under the foramen magnum. Tumors were found lateral to the glossopharyngeal and vagus nerves and medial to the hypoglossal nerve with severe posterior stretching of the brainstem as a result of tumor compression ( Fig. 4D ). The vertebral artery was evident adjacent to the tumor base. We then cut-off the blood supply to the tumor at its base, and gradually removed the tumor. We then repaired Trautman's triangle dura and plugged local using artificial dura mater and plugged muscle tissue on the surface of this region. We then closed the retrosigmoid dura mater, used titanium mini plates and screws to fix the suboccipital bone flap and the mastoid cortex, and closed the suture and incision in a layered manner.

Results

Anatomical Results

Through cadaveric studies, we confirmed that exposure of the CN V–X and ventrolateral upper medulla oblongata was possible via this transmastoid Trautman's triangle approach ( Fig. 2F ). This approach also allowed for avoidance of the need to enter the labyrinth, thus having the potential to better preserve patient hearing.

This retrosigmoid approach is highly versatile, allowing for different degrees of exposure dependent upon the extent of the craniotomy required. When the occipital bone and foramen magnum are removed inferiorly, this approach allows for exposure of the CN VXII and the entire ventrolateral medulla oblongata ( Fig. 3B ).

As the sigmoid sinus was thoroughly exposed via this transmastoid Trautman's triangle combined low retrosigmoid approach, the working area and visibility of the transmastoid Trautman's triangle and the retrosigmoid approaches were improved via posterior and anterior retraction of the sigmoid sinus, respectively.

Clinical Results

We conducted this transmastoid Trautman's triangle combined low retrosigmoid approach in a single patient who was overweight, had a short neck, and was suffering from a large ventral FMM with cerebellar tonsillar herniation. Magnetic resonance imaging (MRI) findings demonstrated that the patient had a 4.2 × 3.5  × 2.2 cm ³ ventral FMM in addition to a cerebellar tonsillar hernia that was causing severe brainstem compression ( Fig. 5A–C ). Postoperative computed tomography confirmed the auditory ossicles to be intact in this patient ( Fig. 5D ). A postoperative MRI confirmed that the lesion was completely removed ( Fig. 5E and F ). After surgery, the patient had fully intact hearing, and their dysdipsia, dysphagia, and instability fully resolved over the following 3 months.

Fig. 5.

Patient imaging findings. ( A–C ) Preoperative axial A, sagittal B T1-weighted MRI and enhanced MRI of coronal C revealed a ventral FMMs with cerebellar tonsillar herniation. This tumor had a maximal 4.2-cm diameter and extended above the level of the arch of C1. The cerebellopontine cistern on the right side of the patient was visible, while the cerebellomedullary cistern was compressed downward by the tumor. ( D ) Postoperative CT bone window revealed intact auditory ossicles. ( E–F ) Postoperative enhanced T1-weighted MRI confirmed complete tumor removal. CT, computed tomography; FMMs, foramen magnum meningiomas; MRI, magnetic resonance imaging.

Discussion

Trautman's triangle faces the cerebellopontine angle, and a transmastoid retrolabyrinthine approach can facilitate its exposure. The approach is a true skull base approach that avoids entering the labyrinth and preserves hearing without manipulation of neural structures. ^{22 23} This approach can be employed when conducting respective surgery aimed at treating vestibulocochlear and trigeminal nerve pathologies, intractable Meniere's disease, aneurysms arising from the posterior circulation, and ventral brainstem pathologies. ^{22 23 24 25} Traditional retrosigmoid approach and its modifications thereof are employed such that the specific bony opening positioning is dependent upon the specific lesion location and characteristics of each individual case. Such approaches represent an alternative means of removing lesions within the cerebellopontine angle, the petroclival region, and the ventral medulla. ^{26 27} In some instances the transmastoid retrolabyrinthine and retrosigmoid approaches have been combined as a means of achieving a wider area of access. ²⁴ In the present report, several reasons led to the selection of the transmastoid Trautman's triangle combined low retrosigmoid approach, and these reasons are detailed further.

Patient Position Requirements

The optimal surgical approach for a given patient can depend upon surgical positioning requirements. ²⁸ When excess flexion or rotation are applied to the neck, this can result in compression or stretching of the spinal cord, brainstem, and surrounding neurovascular. ¹ This is particularly true in FFMs patients suffering from a cerebellar tonsillar hernia, as the compression of the brainstem and spinal cord are already elevated in these individuals, potentially resulting in undesirable positional surgical morbidity. It is thus vital to assess patient flexion and rotation range of motion prior to any surgical operations. In the present report, the patient suffered from both a cerebellar tonsillar hernia and posterior cranial nerve compression, in addition to have a short neck and being overweight. We therefore opted to place the patient in the left lateral position on the operating table, with her head slightly flexed and rotated toward the ground in a Mayfield's fixation apparatus.

Cerebrospinal Fluid Exclusion

It is vital that CSF be excluded when conducting posterior fossa surgeries, as such exclusion reduces brain tissue pressure, thereby minimizing the risk of cerebral hemorrhaging or swelling. CSF is commonly excluded via either presurgical lumbar drainage, or via cerebral cistern during surgery. Based on the cerebellar tonsillar herniation observed in the patient treated in this report, we determined that lumbar drainage had the potential to exacerbate the condition. This patient also exhibited downward compression of the cerebellomedullary cistern, making it more difficult to open. In contrast, we were able to visualize the cerebellopontine cistern on the right side of the patient, making it an ideal site for CSF drainage ( Fig. 5A ). We therefore employed the transmastoid Trautman's triangle combined low retrosigmoid approach only after releasing CSF from the cerebellopontine cistern through Trautman's triangle, while further relieving intracranial pressure via removing portions of the tumor. After relieving intracranial pressure in this patient, we were able to safely remove the remainder of the tumor via the retrosigmoid approach.

Surgical Corridor Evaluation

As tumors become larger, they also become easier to remove via a surgical corridor, with Bruneau and George having defined such corridors as “large” when they provide an access route that is >2 cm in diameter. ⁴ It is possible to further enlarge such a corridor when a tumor displaces structures like the medulla oblongata in a confined region as in the foramen magnum. ¹⁰ The case reported herein also demonstrates that it is possible to easily approach large ventral FMMs without spinal extension via retrosigmoid craniectomy without the need for a partial condylectom, given that such tumor offer a suitably large surgical corridor to facilitate tumor removal.

Sigmoid Sinus Exposure

During cranial base surgery, exposure typically depends upon sacrificing bone to maximize operative space without inducing damage to neurovascular structures. ²⁹ The transmastoid Trautman's triangle combined low retrosigmoid approach offered the advantage of thorough sigmoid sinus exposure. This led to significant improvements in the visibility and working area of the transmastoid Trautman's triangle approach, while the retrosigmoid approach significantly benefited from the posterior or anterior retraction of the sigmoid sinus. ^{23 29 30} This approach also allowed for preservation of the mastoid cortex, ensuring more desirable cosmetic outcomes. Most neurosurgeons are familiar with the traditional retrosigmoid approach, which can readily be extended in different directions as needed to treat tumors in different locations or of different sizes. The far-lateral and related approaches were initially described as an inferolateral extension and modification of the traditional suboccipital retrosigmoid craniotomy. ³¹ Through resection of a wider area of bone, it is possible to achieve a significant increase in exposure at the risk of local vasculature damage, air embolism, hemorrhage, cranial nerve damage, or spinal instability. ¹⁹ The degree to which the occipital condyle and posterior atlantal arch are removed can be determined on a case-by-case basis, with no need for occipital condyle resection in the present case owing to the ample size of the surgical corridor in this patient, and no need for posterior atlantal arch resection as the interior pole of the tumor was above the posterior atlantal arch.

Prevention of Complications

In patients treated for FMMs, preventing postoperative complications can be just as important as properly performing the operation itself. The patient in the present report had suffered from preoperative dysdipsia and dysphagia, necessitating a preoperative tracheostomy and a postoperative nasogastric feeding to prevent aspiration pneumonia. Once they received swallowing training, swallowing function in the patient had improved one month postoperation, and over the next 2 months, the symptoms of dysdipsia, dysphagia, and walking unstable in this patient completely resolved.

Conclusion

FMMs removal via surgical resection remains challenging owing to the high rates of associated morbidity and mortality. It is vital that preoperative imaging findings and consideration of the patient's overall condition be used to determine the optimal surgical approach on a case-by-case basis. The transmastoid Trautman triangle combined low retrosigmoid approach as a complementary approach for the treatment of ventral and ventrolateral FMMs, especially for overweight and patients with short necks and cerebellar tonsillar hernia.

Funding Statement

Funding This work was supported by the Key research and development plan project of Anhui Province (1804h0802023) and the Funding of “Peak” Training Program for Scientific Research of Yijishan Hospital (PF2019003).