EDUCATION CORNER

Challenging Case:
Conservative, Endovascular or Surgical Management of a Patient Presenting with Middle Cerebral Artery Mycotic Aneurysm. A Difficult Decision to ‘MYC’

Arun George, MD
Allegheny Health Network, Pittsburgh, PA

Shobana Rajan, MD
Allegheny Health Network, Pittsburgh, PA

Dr. George
Arun George, MD
Dr. Rajan
Shobana Rajan, MD

Introduction
A 59-year-old patient with no significant medical history was diagnosed with severe mitral regurgitation (MR) and planned for mitral valve replacement (MVR). He had poor dental hygiene, and a facial computed tomography (CT) revealed a periapical abscess. He was started on antibiotics, prophylactic heparin and planned for MVR after medical optimization.

On day four of admission, he had an acute change in his neurologic exam with dysarthria, dysphasia, and confusion. CT head (CTH) and CT angiogram (CTA) was obtained, which revealed a right-sided subarachnoid hemorrhage (SAH) on CTH and a right middle cerebral artery (MCA) bifurcation aneurysm and fusiform aneurysm of the proximal basilar artery on CTA. A diagnostic digital subtraction angiography (DSA) for further evaluation of the aneurysms revealed a right proximal M2 branch dissecting fusiform pseudoaneurysm measuring 7x7x7 mm3, likely mycotic.

As the morphology and location of the aneurysm were not ideal for either endovascular or surgical intervention, the aneurysm was initially managed conservatively with antibiotics, blood pressure control, and close monitoring of the aneurysm via imaging. Repeat CTA was obtained three days later, which demonstrated an increase in the size of the aneurysm. The decision was made to take the patient to the operating room (OR) for the right MCA aneurysm clipping with possible bypass the next day. A DSA was completed to evaluate further the aneurysm and surgical planning; it demonstrated an increase in the aneurysm size.

On returning from the diagnostic angiogram, the patient no longer followed commands and had rapid deterioration of his neurological status. His trachea was emergently intubated and underwent CTH, which showed extensive hemorrhage. He was emergently taken to the OR for a right-sided decompressive hemicraniectomy and MCA aneurysm repair. The decision was made to ligate the distal right MCA M1 segment to ensure no further hemorrhage from the diseased vessel, and an external ventricular drain (EVD) was also placed at this time. Postoperatively, the patient was kept intubated, and his neurologic exam remained poor. However, his condition did not improve, and the patient died soon after terminal extubation on comfort measures.

Discussion
When involved in caring for a patient with mycotic aneurysms, these are a few questions that should be considered.

  1. Why are mycotic aneurysms considered dangerous?
  2. What is the gold standard for the diagnosis of mycotic aneurysm?
  3. What are the management strategies available for mycotic aneurysms?
  4. What are the factors that influence the timing and modality of treatment of mycotic aneurysm?
  5. Should the cause or effect be treated first? Which procedure should be performed first- the infected cardiac valve replacement or mycotic aneurysm coiling/clipping?

History
In 1869, Church described a causal link between intracranial aneurysm and endocarditis.1 The term “mycotic aneurysm” was conceived by William Osler in 1885 in his "Gulstonia lectures” on malignant endocarditis.2 This term maybe a misnomer in many ways, as a variety of bacteria, fungi, mycobacteria, and viruses could also cause such aneurysms.

Etiology
Mycotic aneurysms are rare and localized representing 0.7–5.4% of all intracranial aneurysms.3 They arise from infection of either a normal arterial wall or a preexisting aneurysm. It can be caused by numerous pathogens and most frequently is bacterial in origin.4 Mycotic aneurysms result from gradual destruction of the arterial wall by the infection. The source of this can be classified as intravascular such as in infective endocarditis or extravascular as in meningitis and immunosuppressed states.5,6 Even though antimicrobial medications has considerably reduced the incidence of endocarditis in many economically developed countries; it still remains prevalent due to the rise in use of prosthetic valves and intravenous drug abuse with majority of mycotic aneurysms emanating from left heart bacterial endocarditis.7

Pathogenesis
There is an acute infiltration of the vascular wall media and adventitia by polymorphonuclear cells. Streptococci and Staphylococcus aureus are the most common organisms.8 The development and growth of the aneurysm is further aided by the hydrostatic pulsations and a thrusting force against the infected arterial wall.9 Mycotic aneurysms are insidious remaining asymptomatic for prolonged periods and have been associated with a high case fatality rate.

Mycotic aneurysms rarely undergo spontaneous thrombosis, and unlike berry aneurysms, size does not reliably corelate with potential rupture. These aneurysms can present in many ways, some small mycotic aneurysms can rupture leading to fatal bleed, while many others may not bleed but have the potential to increase in size and become symptomatic by compressing nearby structures. Mortality rates from these aneurysms were high, around 80% after rupture and 30% in unruptured aneurysms.10

However, a more recent case series has shown lower mortality rate of 12–32%. Various risk factors have been associated with increased mortality including advanced age, fungal origin of the aneurysm, patients with meningitis, and in aneurysms located in the vertebrobasilar arterial territory.11 The gold standard for the diagnosis of mycotic aneurysms is DSA,12 even though CT angiography and magnetic resonance imaging (MRI) can also be utilized.13

Management
No widely accepted guidelines exist for the management of mycotic aneurysms. In addition to the lack of large studies this lack of standardized guidelines can be attributed to the rare nature of these aneurysms and the clinical variability. This lack of standards makes the management of mycotic aneurysms variable and provider dependent. Antimicrobial therapy has been used alone and in conjunction with endovascular or surgical interventions depending on the patient’s clinical condition, location, and nature of the aneurysm.13The management of mycotic aneurysms varies depending on if it is ruptured or not. The indications for the surgical and/or endovascular treatment of mycotic aneurysms remain controversial, and the success of these interventions depends on a multitude of factors including patient comorbidities, aneurysm morphology and the presence of associated ICH.14

A) Conservative: Patients who are at a high surgical risk maybe treated with antibiotics alone for 4 to 6 weeks.15 These patients are ideally followed up with serial imaging and if it is noted that the aneurysm size remains the same or expanding, endovascular or surgical intervention maybe required.

B) Endovascular: In case the mycotic aneurysm is surgically inaccessible or if there are multiple mycotic aneurysms, endovascular intervention maybe the modality of choice.16 Advantages of this intervention includes it being less invasive hence presenting an opportunity to avoid general anesthesia which would be ideal in these patients who often have cardiac valvular dysfunction.9

C) Surgery: Surgical intervention is preferred in patients with significant aneurysmal bleed and when mass effect is present. It is suitable in young patients who are symptomatic and have accessible mycotic aneurysms.17

Timing: If there is no neurological injury threatening patient outcome, cardiac valve surgery can be done initially. Ideally, a bioprosthetic valves should be used, precluding the requirement for postoperative anticoagulation.18In case of a ruptured aneurysm where surgery may be preferred, there should be at least a 2-week interval between aneurysm clipping and the cardiac procedure.19

Anesthetic Considerations: Pre anesthetic evaluation should include grading of the SAH using modified Hunt and Hess grading. Some of the considerations for an anesthesiologist dealing with aneurysmal SAH include hyperglycemia, hypovolemia, hyponatremia/hypernatremia, and hypokalemia which may need correction. During induction, care should be taken to avoid hypertension which may precipitate a rebleed. On the contrary side, some patients may develop myocardial dysfunction (neurogenic stunned myocardium) and may be prone to hypotension during induction. Normocarbia should be maintained as both hyper- and hypocarbia could be detrimental. Some patients may have an EVD coming into the operating area, ICP should be ideally maintained below 20 mmHg. Jugular venous oximetry is useful tool to guide the intraoperative fluid, ventilation and oxygenation therapy. Electroencephalogram (EEG)and intraoperative neurophysiological monitoring aid in timing burst suppression during temporary clipping and help in timely detection of cerebral ischemia, respectively. A brief period of hypertension during the temporary clipping may be helpful to maintain perfusion and in cases where temporary clipping is not possible, temporarily arresting blood flow can be done using adenosine or rapid ventricular pacing.20

Conclusion
Mycotic aneurysms are insidious in nature as they may not produce any symptoms for prolonged periods. There has not been much reporting of experiences concerning the management of mycotic aneurysms and hence this topic remains controversial.  The clinical variability and rarity of this condition along with the lack of large, randomized trials (RCT) has attributed to no widely accepted standards or guidelines for the management of mycotic aneurysms. Antimicrobial treatment with or without surgical or endovascular intervention is utilized depending on several factors. Timing and selection of these modalities are crucial as these aneurysms have also been associated with a high fatality rate in case of rupture. There are several considerations an anesthesiologist should keep in mind when dealing with patients with intracranial mycotic aneurysmal bleeds. More RCT’s to help develop standards to guide clinical decision-making and treatment of mycotic aneurysms would be highly beneficial.

References

  1. Church W. Aneurysm of the right cerebral artery in a boy of thirteen. Trans Pathol Soc Lond. 1869;20:109.
  2. Osler W. Culstonian lectures on malignant endocarditis. The Lancet. 1885;125(3212):505-8
  3. Nakahara I, Taha MM, Higashi T, et al. Different modalities of treatment of intracranial mycotic aneurysms: report of 4 cases. Surg Neurol. 2006;66:405-9.
  4. Dhomne S, Rao C, Shrivastava M, Sidhartha W, Limaye U. Endovascular management of ruptured cerebral mycotic aneurysms. Br J Neurosurg. 2008;22:46-52.
  5. Suwanwela C, Suwanwela N, Charuchinda S, et al. Intracranial mycotic aneurysms of extravascular origin. Journal of neurosurgery. 1972;36:552-9.
  6. Rout D, Sharma A, Mohan PK, et al. Bacterial aneurysms of the intracavernous carotid artery. J Neurosurg. 1984;60:1236-42.
  7. Corr P, Wright M, Handler LC. Endocarditis-related cerebral aneurysms: radiologic changes with treatment. Am J Neuroradiol. 1995;16:745-8.
  8. Kannoth S, Thomas SV. Intracranial microbial aneurysm (infectious aneurysm): current options for diagnosis and management. Neurocrit Care. 2009;11:120.
  9. Ducruet AF, Hickman ZL, Zacharia BE, et al. Intracranial infectious aneurysms: a comprehensive review. Neurosurgical Rev. 2010;33:37-46.
  10. Bohmfalk GL, Story JL, Wissinger JP, Brown WE. Bacterial intracranial aneurysm. J Neurosurg. 1978;48:369-82.
  11. Kannoth S, Iyer R, Thomas SV, Furtado SV, et al. Intracranial infectious aneurysm: presentation, management and outcome. J Neurologic Sci. 2007;256:3-9.
  12. Bartakke S, Kabde U, Muranjan MN, et al. Mycotic aneurysm: an uncommon cause for intra-cranial hemorrhage. Indian J Pediatr 2002;69:905-7.
  13. Ducruet AF, Hickman ZL, Zacharia BE, et al.Intracranial infectious aneurysms: a comprehensive review. Neurosurgical Rev 2010;33:37-45.
  14. Sugg RM, Weir R, Vollmer DG, Cacayorin ED. Cerebral mycotic aneurysms treated with a neuroform stent: technical case report. Neurosurgery. 2006;58:E381.
  15. Phuong LK, Link M, Wijdicks E. Management of intracranial infectious aneurysms: a series of 16 cases. Neurosurgery. 2002;51:1145-52.
  16. Chapot R, Houdart E, Saint-Maurice JP, et al. Endovascular treatment of cerebral mycotic aneurysms. Radiology. 2002;222:389-96.
  17. Lüders JC, Steinmetz MP, Mayberg MR. Awake craniotomy for microsurgical obliteration of mycotic aneurysms: technical report of three cases. Operative Neurosurgery. 2005;56(suppl_1):ONS-E201.
  18. Bartakke S, Kabde U, Muranjan MN, et al. Mycotic aneurysm: an uncommon cause for intra-cranial hemorrhage. Indian J Pediatr. 2002;69:905-7.
  19. Yuan SM, Wang GF. Cerebral mycotic aneurysm as a consequence of infective endocarditis: A literature review. Cor et vasa. 2017;59:e257-65.
  20. Sharma D. Perioperative Management of Aneurysmal Subarachnoid Hemorrhage A Narrative Review. Anesthesiology. 2020;133:1283-305.
  21. Zanaty M, Chalouhi N, Starke RM, et al. Endovascular treatment of cerebral mycotic aneurysm: a review of the literature and single center experience. Biomed Res Int. 2013;2013:151643.

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