Treatment of Coalescent Mastoiditis with Posterior Fossa Epidural Abscess Via a Transmastoid-Retrosigmoid Approach—A Case Report

Introduction: Epidural abscess is a known complication of coalescent mastoiditis. Depending on the route of bony erosion through the temporal bone, the abscess can involve either the middle or posterior cranial fossae. In this report, we describe a case of coalescent mastoiditis resulting in a large posterior fossa epidural abscess extending to the midline occiput with associated mass effect. We also describe a unique surgical approach to drain this abscess via a transmastoid-retrosigmoid approach. This approach provided access to both the mastoid disease and the epidural abscess and obviated the need for a separate posterior fossa burr hole and its added morbidity.

Case Description: A 23-year-old male was transferred with a one-month history of persistent left otitis media and a posterior fossa epidural abscess. CT and MRI demonstrated a left-sided coalescent mastoiditis and multiloculated posterior fossa epidural abscess. The abscess extended around the lateral and posterior aspects of the cerebellum to the midline occiput and superiorly to the tentorium cerebelli. Mass effect on the left cerebellum was demonstrated with transtentorial herniation, absent flow through the left transverse and straight sinuses, and compression of the fourth ventricle. A left ear tube was placed upon patient arrival with the immediate return of purulent middle ear fluid. The patient was subsequently taken to the operating room for a mastoidectomy and drainage of the epidural abscess. The initial operative plan was for a separate posterior fossa burr hole to drain the intracranial portion of the abscess. However, intraoperative findings and image guidance suggested that the abscess could be accessed using a transmastoid-retrosigmoid approach. This allowed both the mastoid and intracranial disease to be addressed without the additional morbidity of a separate posterior fossa burr hole.

The mastoidectomy was performed first with removal of purulence and granulation tissue from the mastoid cavity. The sigmoid sinus was identified and the pre-sigmoid and post-sigmoid posterior fossa dura were exposed. The retrosigmoid craniectomy was extended inferiorly along the post-sigmoid dura and a large coalescent area was identified. The bone posterior to this area was then removed, revealing a tract leading from the area of coalescence to the epidural space. The epidural space was entered at this location with immediate return of copious purulent fluid. A pediatric feeding tube was gently passed into the epidural space to disrupt any locules with further return of frank purulence. Micro-instrumentation was used to dissect in the epidural space to ensure that all abscess pockets were drained. The patient had an uneventful postoperative course with no postoperative neurological deficits and he made a full recovery.

Discussion: This patient presented with coalescent mastoiditis complicated by an extensive posterior fossa epidural abscess. Despite its size, it was effectively treated via a transmastoid-retrosigmoid craniectomy requiring no additional burr hole thus minimizing operative morbidity ([Fig. 1]).

Fig. 1 (A) CT demonstrating coalescent mastoiditis with two areas of dehiscence (arrows) of the temporal bone into the posterior fossa.

(B) MRI demonstrating the epidural abscess tracking from the temporal bone into the posterior fossa.

(C) Postoperative MRI after drainage of the abscess.

Publication History

Article published online:
15 February 2022