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Pediatric infratentorial subdural empyema: A case report

Background: Infratentorial subdural empyemas in children are extremely rare and potentially lethal intracranial infections. Delay in diagnosis and therapy is associated with increased morbidity and mortality. Case Description: A 4-year-old boy presented with cerebellar signs following a failed treatment of otitis media. Imaging studies revealed a subdural empyema and left transverse and sigmoid sinus thrombosis. The empyema was evacuated operatively and antibiotic treatment was initiated and administered for 6 weeks. The patient recovered fully and was discharged 4 weeks following the evacuation of the empyema. Conclusion: While prompt identification and treatment of subdural infratentorial empyemas are crucial for favorable outcomes, their diagnosis in children might be initially missed. This is, in part because they are so rare and in part, because imaging artifacts arising from the complex posterior fossa anatomy may obscure their presence in the computer tomography (CT) scan. Therefore, high level of suspicion is necessary, given the appropriate history and clinical presentation. In children, this is a recent history of protracted otitis media and central nervous system symptomatology—cerebellar or other.


INTRODUCTION
A subdural empyema is defined as the focal intracranial collection of purulent material between the dura and the arachnoid mater. Most often, it presents as a complication of other pathologies such as sinusitis, mastoiditis, and bacterial meningitis or posttraumatically. [3] It is a medical emergency requiring prompt identification and treatment with surgical evacuation and intravenous antibiotics; delay in therapy is associated with increased morbidity and mortality. [1] Subdural empyemas are only rarely located in the posterior fossa. Their rarity and the limitations of computed tomography (CT) imaging in the evaluation of the posterior fossa make subdural empyema especially prone to delayed diagnosis. In this report, we present a case of infratentorial subdural empyema that was successfully treated in our institution. A 4-year-old boy presented to the pediatric emergency department with symptoms of cerebellar ataxia and gait disturbances. Sixteen days prior to that, his parents had consulted a primary care physician due to left earache and fever. No purulent discharge from the ear was evident at the time. Then, the patient was diagnosed with otitis media and was prescribed oral amoxicillin-clavulanic acid. Due to symptoms persistence, treatment was subsequently switched to oral cefuroxime.

CASE REPORT
Upon presentation to our emergency department, a complete blood count showed leukocytosis and neutrophilia. The prominence of cerebellar symptoms raised suspicion for an intracranial pathology and thus an emergency contrast-enhanced CT scan was performed. The scan revealed a multilobular cystic lesion with peripheral contrast enhancement, located in the subdural space of the posterior fossa, in contact with the tentorium cerebelli superiorly [ Figure 1]. The lesion was compressing the left cerebellar hemisphere, which appeared edematous and the cerebellar midline was displaced by 9 mm. Moreover, the left middle ear cavity, ipsilateral mastoid air cells, and partially the left ethmoid air cells were occupied by fluid. The left transverse sinus could not be recognized in the scan. Subsequently, in order to evaluate more accurately the extent of the posterior fossa collection and to address the CT findings suggesting left transverse sinus thrombosis, a magnetic resonance imaging (MRI) scan and a magnetic resonance venography (MRV) were conducted. MRI confirmed the presence of extensive infratentorial subdural empyema over the left cerebellar hemisphere, accompanied by displacement and edema of the left cerebellum. MRV revealed diminished flow through the left transverse sinus and no flow through the left sigmoidal sinus [ Figure 2], and these findings were consistent with sinus thrombosis.
Consecutively, an emergency operation was scheduled. A left suboccipital craniotomy was performed. The transverse sinus was recognized and the dura was incised. Following traction of the cerebellum, the subdural space was expanded and the purulent collection was encountered. Cultures from the purulent fluid were obtained and the empyema was evacuated.

Intravenous
antibiotic treatment with piperacillin-tazobactam and teicoplanin was initiated. After 4 days the patient had no fever, no neurological deficits, and was ambulatory. Follow-up MRI scan documented the successful evacuation of the empyema and subsiding inflammation [ Figure 3]. Three weeks into the treatment, a morbilliform skin rash was developed on the patient's trunk, face, and limbs consistent with drug allergic reaction. The antibiotic treatment was then switched to oral clarithromycin, which was administered for 3 more weeks, for a total of 6 weeks of antibiotic treatment. The patient was discharged from the hospital 4 weeks after the operation.

DISCUSSION
Infratentorial subdural empyema is an extremely rare clinical entity both in children and in adults. Apart from the Madhugiri et al. [6] case series, which consisted of 27 patients with mean age of 10 years, there is remarkable paucity in the literature. Sengul [12] reports one such case in a 15-year-old boy, whereas Gupta et al. [4] reported a case of 17-year-old patient. In both studies, the empyema followed a middle ear infection and presented mimicking pyogenic meningitis. There is also a case report [5] of a posterior fossa subdural empyema in a 14-month old boy arising from a dermal sinus tract. Finally, the Farah et al. [9] case series of 20 pediatric subdural empyemas includes just one case where posterior fossa was involved. The large Nathoo et al. [8] case series of infratentorial empyemas aims to provide an  estimate for the incidence of this clinical entity; their 13 cases of subdural infratentorial empyemas accounted for about 0.4% of all the intracranial suppuration cases they encountered during their study period. Table 1 provides an overview of all the cases of pediatric infratentorial subdural empyemas described in the literature.
Our patient presented with cerebellar signs and a recent history of otitis media. In the Madhugiri series, [6] 40% of the patients and just 13% of patients of the Nathoo [8] series presented with cerebellar symptomatology. The most common presenting symptoms in both series were meningism, depressed level of consciousness, fever, and ear discharge. Seizures, hemiparesis, or cranial nerve palsy could also be part of the presentation. Furthermore, the patients of the Borovich [2] and Morgan [7] series described similar symptoms and signs. It is noteworthy that subdural empyemas without treatment are invariably fatal. Prompt diagnosis and treatment with intravenous antibiotics and neurosurgical intervention are necessary in order to not only increase the survival rates but also to decrease the gravity of any neurological sequelae. [10] The primary cause of infratentorial empyemas is a complicated otogenic infection. This is the case for our patient who underwent a prolonged antibiotic treatment for an otitis media infection that proved resistant. The same course was described in 19 out of 22 Nathoo's [8] patients, 26 out of 27 Madhuguri [6] patients, in all 3 Borovich [2] cases, and 5 out of 7 Morgan's patients. [7]

Complications Outcome
Madhugiri et al. [6] 27  In terms of diagnosis, high clinical suspicion is the first step. Despite the greater accuracy of MRI scans in diagnosing intracranial pathologies, the initial imaging study of choice is CT scan, due to its speed and availability. [2,6,8] However, the complex osseous posterior fossa anatomy produces imaging artifacts that may obscure the purulent collection. As a result, diagnosis of posterior fossa empyemas may be initially overlooked, thus delaying appropriate treatment. [13,14] MRI scan is more time-consuming-a consideration that is taken into account for a patient with altered mental state [6] -but it is the preferred imaging modality, especially diffusion weighted imaging sequences, which can distinguish suppurative collections from reactive subdural effusions. [14] The culture of the purulent collection we obtained intraoperatively did not identify any pathogens. This is a frequently encountered mischief in subdural empyemas. Sterile collections are reported in the Nathoo [8] series (5 out of 22 cases), Madhugiri [6] series (7 out of 27), and Morgan series [7] (3 out of 7 cases). In other smaller reports, for example the two Taha patients, cultures of the suppurative fluid were sterile. [13] Nevertheless, when a pathogen was to be isolated, Proteus mirabilis was the most frequent causative species in Nathoo et al. study, and polymicrobial culture was the second most frequent culture result. In the Madhugiri et al. [6] study, polymicrobial cultures and nonhemolytic streptococci were the most prevalent results. Madhugiri et al. [6] noted that cases with sterile cultures tended to have higher chance for re-accumulation of the suppuration and, thus, necessitating a second operation for re-evacuation. A repeat operation was required for 5 out of 7 cases with sterile cultures, compared to 1 out of 20 cases with nonsterile cultures. Agrawal et al. [1] considered sterile culture of the subdural collection as one of the unfavorable prognostic factors.
Finally, the course of our patient was complicated with left transverse and sigmoid sinus thrombosis. Sinus thrombosis was encountered in one of the Madhugiri [6] patients, two of Nathoo's [8] patients, two of Morgan's [7] patients, and in a case report by Sahjpaul. [11] Nathoo et al. [8] reported significant morbidity for their patients that exhibited this complication.
Infratentorial subdural empyemas compared to the more common supratentorial variants are associated with higher mortality. This has been attributed to delays in diagnosis and treatment. [14] Therefore, it is worth including this threatening clinical entity in the differential diagnosis list, despite its rarity and despite an initial negative or inconclusive CT scan.

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Conflicts of interest
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