- Department of Neurosurgery, University of Illinois College of Medicine, Rockford, Illinois,
- Department of Neurosurgery, Massachusetts General Hospital, Boston, Massachusetts, United States.
- Infectious Diseases Division, Massachusetts General Hospital, Boston, Massachusetts, United States.
- Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts, United States.
Gavin Dunn, Department of Neurosurgery, Massachusetts General Hospital, Boston, Massachusetts, United States.
DOI:10.25259/SNI_871_2022Copyright: © 2022 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Lydia Leavitt1, Amy Baohan2, Howard Heller3, Liana Kozanno4, Matthew P. Frosch4, Gavin Dunn2. Surgical management of an abscess of the insula. 23-Dec-2022;13:591
How to cite this URL: Lydia Leavitt1, Amy Baohan2, Howard Heller3, Liana Kozanno4, Matthew P. Frosch4, Gavin Dunn2. Surgical management of an abscess of the insula. 23-Dec-2022;13:591. Available from: https://surgicalneurologyint.com/surgicalint-articles/12072/
Background: Mass lesions within the insular are diagnostically and surgically challenging due to the numerous critical cortical, subcortical, and vascular structures surrounding the region. Two main surgical techniques – the transsylvian approach and the transcortical approach – provide access to the insular cortex. Of the range of pathologies encountered, abscesses in the insula are surprisingly rare.
Case Description: A 34-year-old patient was admitted for surgical resection of a suspected high-grade glioma in the insula of the dominant hemisphere. A rapid clinical decline prompted emergent neurosurgical intervention using a transsylvian approach. Surprisingly, abundant purulent material was encountered on entering the insular fossa. Pathological analysis confirmed an insular abscess, although a source of infection could not be identified. The patient required a second evacuation for reaccumulation of the abscess and adjuvant corticosteroids for extensive cerebral edema.
Conclusion: An abscess located in the insular cortex is an incredibly rare occurrence. Surgical management using the transsylvian approach is one option to approach this region. Familiarity with this approach is thus extremely beneficial in situations requiring emergent access to the dominant insula when awake mapping is not feasible. In addition, treatment of abscesses with adjuvant corticosteroids is indicated when extensive, life-threatening cerebral edema is present.
Keywords: Brain abscess, Infection, Insula, Transsylvian approach
Brain abscesses are life-threatening infections within the brain parenchyma. The infection begins as a localized area of cerebritis before rapidly developing into a mass lesion composed of an encapsulated collection of pus with surrounding edema. Early diagnosis and treatment are imperative to reduce the risk of mortality, which reaches a rate of approximately 20% at 1 year.[
A 34-year-old right-handed woman with diabetes mellitus type two, obesity class two, and a history of migraines presented to the emergency department after a self-resolving 5 min episode of paresthesias in her right hand, arm, and face. She also noticed a foul taste in her mouth reminiscent of French onion soup. These symptoms occurred in the setting of a 7-day unremitting headache worsened by bright lights. While in the emergency department, she experienced a second episode of paresthesias and was given lorazepam and levetiracetam for suspected focal sensory seizures. She had stable vital signs and her physical examination was unremarkable aside from trace right facial asymmetry.
A head CT demonstrated a hyperattenuating focus in the left insular region surrounded by an area of low attenuation, suggestive of vasogenic edema [
The patient was transferred to Massachusetts General Hospital (MGH) for the management of a presumed left insular tumor. Several days following her admission to MGH and before a planned awake left craniotomy, she developed expressive aphasia and intermittent disorientation to time and place. An urgent CT demonstrated enlargement of the mass to nearly 5.0 cm. Given the rapid rate of change in the size of the mass, we suspected that the insular lesion was an abscess and thus obtained a brain MRI which showed the mass to be peripherally enhancing and now obviously restricting diffusion. Her cerebral edema had also significantly worsened, causing a 2 mm midline shift to the right and mass effect on the left lateral ventricle and basal ganglia [
Serial brain magnetic resonance imaging (MRI) scans performed throughout the patient’s hospital course: (a) on admission to MGH showing left insular mass with irregularly marginated peripheral enhancement with central necrotic and hemorrhagic foci causing mass effect and a 2 mm midline shift to the right. Fluid-attenuated inversion recovery (FLAIR) imaging demonstrates surrounding edema and diffusion-weighted imaging (DWI) demonstrates restricted diffusion in the center of the lesion. (b) Following acute clinical decline before first surgery revealed an interval increase in the left insular lesion with more well-defined peripheral enhancement. Mass effect has progressed causing increased rightward midline shift. FLAIR imaging shows increased peripheral edema. (c) Postoperative demonstrating a mildly decreased size in the lesion. There is a loculated rim-enhancing component along the superolateral margin of the resection cavity and a focus of apparent discontinuous rim enhancement along the inferolateral posterior aspect of this loculation. (d) Surveillance MRI on post operative day 7 shows an expansion of the previously partially collapsed appearance of the abscess cavity walls. Extensive FLAIR hyperintensity with mass effect surrounding the abscess cavity has increased causing increased extracranial herniation and left to right midline shift. The images show T1 postcontrast axial (labeled as 1), sagittal (labeled as 2), and coronal (labeled as 3); axial FLAIR (labeled as 4); and axial DWI (labeled as 5).
Because the patient was herniating, a decompressive left frontotemporal craniectomy was planned followed by a transsylvian approach to access and drain the presumptive insular abscess.
After exposure of the Sylvian fissure, we found that inflammatory phlegmon had layered over the entire fissure and surrounded the Sylvian veins. After much exploration, a small arachnoid window was identified and opened in the distal aspect of the fissure as we followed an M4 branch into the fissure. This opening was carried anteriorly and deepened, and as we dissected between the M2 branches, a rush of purulent fluid was encountered. A sample of this material was sent for aerobic and anaerobic bacterial, fungal, and mycobacterial testing. The cavity in the insula was then entered, and the remaining purulence was evacuated. After irrigating the region, friable inflammatory-appearing tissue was noted surrounding the cavity walls. The patient’s bone flap was left off to allow for maximal brain decompression. She was started on vancomycin, cefepime, and metronidazole for the treatment of an intracerebral abscess. A postoperative head CT showed excellent brain decompression with a reduction of the midline shift and resolution of herniation. A loculated rim-enhancing component along the superolateral margin of the dominant abscess cavity seen on postoperative MRI was suspicious for residual abscess [
Culture of the purulent material grew Streptococcus intermedius – a bacterium normal to the oral cavity and upper respiratory tract flora. An odontogenic infection was investigated, but a dental examination showed no clinical or radiographic evidence of acute or chronic intraoral infections. There was no history of dental infections or dental procedures other than routine cleaning and no oral piercings. Investigation into other possible sources also failed to find evidence of infection: (1) no valvular vegetations on transthoracic echocardiogram, (2) no pulmonary arteriovenous malformations seen on chest CT, (3) negative blood cultures, (4) negative human immunodeficiency virus antigen/antibody tests, and (5) no past medical history, family history, or examination findings suggesting hereditary hemorrhagic telangiectasia.
After 1 week of antibiotics, a surveillance brain MRI on POD 7 showed a likely recurrence of the abscess with rightward midline shift progression, worsening parenchymal herniation through the craniectomy defect, and subfalcine and uncal herniation [
A postoperative head CT showed a collapsed abscess cavity and decreased parenchymal herniation through the craniectomy site. Histologic examination showed portions of brain with abundant necrosis and a dense neutrophilic infiltrate, consistent with abscess and excluding a superimposed underlying malignancy [
One week after surgery, head CT revealed a re-expansion of the previously collapsed abscess cavity, significant edema with mass effect, and a subcutaneous hematoma [
(a) Postsurgical changes from left-sided craniectomy with extensive edema of brain parenchyma causing herniation of the left cerebral hemisphere through the craniectomy defect, minimal rightward midline shift, and effacement of the left lateral ventricle. (b) A follow-up scan 2 months after discharge shows improving cerebral edema and no abnormal enhancement to suggest persistent or recurrent abscess. T1 postcontrast axial, sagittal, and coronal (c), axial fluid-attenuated inversion recovery (d), and axial diffusion-weighted imaging (e) sequences from her most recent follow-up MRI taken 3 months after discharge shows substantially decreased brain herniation and swelling of the left cerebral hemisphere with residual enhancement within the insula and mild residual FLAIR hyperintensity involving the left frontal lobe, insula, and left temporal lobe.
The patient continued to improve and was discharged home on steroids and antibiotics. She ultimately completed 1 month of steroid therapy and 6 weeks of oral metronidazole and penicillin G. She continues to be followed outpatient and has returned to her neurologic baseline. A 2-month follow-up head CT demonstrated improving cerebral edema and no evidence of a persistent or recurrent abscess [
The insular cortex is a rare location for cerebral abscesses with very few cases published in the literature. The most common locations for cerebral abscesses are, of decreasing frequency: the frontal and temporal lobes; frontal-parietal region; parietal lobe; cerebellum; and occipital lobe.[
In this case, the initial imaging findings were more consistent with a high-grade neoplasm, and thus, we had prepared to perform an awake left craniotomy for tumor resection using neuromonitoring. Once the patient’s condition declined rapidly and the imaging more clearly demonstrated an abscess etiology, our clinical decision-making changed. If the patient was clinically stable, stereotactic needle drainage would have represented a very reasonable option. However, the patient’s clinical herniation compelled us to proceed with a more aggressive approach to decompress the left hemisphere and perform a microsurgical evacuation.
Intracranial abscesses are treated with surgical drainage followed by long-term antibiotic treatment.[
Steroid administration is often avoided in patients with cerebral abscesses out of concern for worsened patient outcomes.[
Neurosurgical procedures involving the insular cortex can be challenging. Situated in the depths of the Sylvian fissure, the insular cortex is covered by the frontal, temporal, and parietal lobes and hidden under a dense network of critical arterial and venous blood vessels.[
A representative illustration of the abscess through the transsylvian approach in relation to the four insular zones. The transsylvian approach preserves the overlying eloquent cortex in the frontal and temporal lobes but requires working between critical vascular structures including branches of the MCA and superficial Sylvian vein. The Berger-Sanai classification separates the insular cortex into four zones using perpendicular lines through the Sylvian fissure and the foramen of Monro. Zone 1 is above the Sylvian fissure and anterior to the foramen of Monro. Zone 2 is superior to the Sylvian fissure and posterior to the foramen of Monro. Zone 3 is inferior to the Sylvian fissure and posterior to the foramen of Monro. Zone 4 is inferior to the Sylvian fissure and anterior to the foramen of Monro.
The TS approach, involves splitting the Sylvian fissure and meticulous dissection of the Sylvian and peri-Sylvian vessels.[
Several critical vascular structures traverse and surround the Sylvian fissure and insula. Veins within and overlying the Sylvian fissure are preferably preserved as coagulation can increase venous pressure in the remaining Sylvian veins, particularly in patients with poor collateral outflow through the superior sagittal sinus or vein of Labbé.[
Eloquent cortical regions involved in speech, language, and motor functions also surround the operative corridor.[
The TC approach involves performing frontal, parietal, or temporal operculum corticectomies to create windows of access to the insular cortex.[
To ensure parenchymal transgression occurs through functionally silent cortex, the TC approach requires intraoperative cortical and subcortical mapping to locate regions critical for speech, language, motor, and cognitive function.[
Intraoperative cortical and subcortical stimulation is not entirely infallible and carries its own risks. Direct cortical stimulation can cause intraoperative seizures,[
The transsylvian and TC approaches may also be combined in certain instances, particularly in cases of large insular masses and those that extend into adjacent brain structures, in which aspects of the target are best accessed by a hybrid approach.
This case demonstrates the diagnostic and surgical challenges of a mass lesion within the insula. Gliomas are relatively common in the insular lobe and paralimbic region – up to 25% of low-grade and 10% of high-grade gliomas are found in this region.[
All patients with cerebral abscess are treated with long-term antibiotics which are often initiated after stereotactic needle aspiration or, less preferably, before if drainage of the presumed abscess is delayed. Open surgical evacuation becomes necessary when there are signs of increased intracranial pressure, a progressive increase in the abscess diameter, or abscess material reaccumulates despite needle aspiration attempts. Adjuvant corticosteroids are warranted when extensive cerebral edema – or reaccumulating sterile inflammatory fluid – is present.
Surgical access to insular abscesses or other insular pathologies is challenging due to numerous critical structures within and surrounding this region: the frontal, parietal, and temporal opercula contain eloquent cortex necessary for speech and motor functions; surrounding the insula are fasciculi involved in speech and directly medial to the insula are basal ganglia structures; and overlying and coursing through the insula are critical vessels supplying the insula, cortex, and basal ganglia.
Access to the insula can be achieved through the TS or TC approach. In the TS approach, the surgeon splits the Sylvian fissure and follows branches of the MCA, creating a dissection plane along the opercula to the insular cortex. While this approach offers limited surgical exposure, intraoperative cortical mapping is not imperative, and it can, therefore, be used during emergent situations. Conversely, the TC can provide greater surgical exposure but requires intraoperative cortical and subcortical mapping to ensure that corticectomies are performed through the functionally silent cortex.
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The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.
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