Indications

• Patients with mass effect on computed tomographic (CT) scan or with neurological dysfunction or deterioration referable to the lesion should undergo operative intervention. Mass effect on CT scan is defined as distortion, dislocation, or obliteration of the fourth ventricle; compression or loss of visualization of the basal cisterns, or the presence of obstructive hydrocephalus.
• Patients with lesions and no significant mass effect on CT scan and without signs of neurological dysfunction may be managed by close observation and serial imaging.

Timing

• In patients with indications for surgical intervention, evacuation should be performed as soon as possible because these patients can deteriorate rapidly, thus, worsening their prognosis.

Methods

• Suboccipital craniectomy is the predominant method reported for evacuation of posterior fossa mass lesions, and is therefore recommended.

Posterior fossa injury is rare, occurring in less than 3% of head injuries in most published series8, 12, 22. The vast majority of these series deal exclusively with posterior fossa epidural hematomas (EDH), representing 1.2 to 12.9% of all EDH7, 20, 21, 30. A small number of observational studies address subdural and intraparenchymal hematomas of the posterior fossa5, 8, 17, 22, 24, representing 0.5 to 2.5% and 1.7% of all subdural hematomas and intraparenchymal hematomas, respectively22, 24. Additionally, there is a separate literature that focuses on parturitional hemorrhages, up to 48% of which primarily involve the posterior fossa27. Because of the physiology and anatomy of the neonate, and the unique mechanism of these injuries, this subgroup of patients warrants independent analysis, and will not be addressed in these Guidelines.

Despite the rarity of these lesions, the importance of timely recognition and surgical evacuation, when indicated, cannot be overstated. Many patients can undergo rapid clinical deterioration because of the limited size of the posterior fossa and the propensity for these lesions to produce brainstem compression.

A MEDLINE computer search using the following key words: "posterior fossa" or "cerebellum" or "cerebellar" or "occipital" and "subdural" or "epidural" or "extradural" or "intradural" or "parenchymal" or "intraparenchymal" or "intracerebellar" or "fracture" between 1975 and 2001 was performed. A total of 1828 documents were found. The search was narrowed to include the key words: "surgery" or "operative" or "craniotomy" or "craniectomy" or "decompressive craniectomy" or "repair" and "trauma" or "traumatic" or "TBI" or "CHI." A total of 430 articles were found. A tertiary search adding the key words "contusion," "hemorrhagic contusion," "surgical decompression," "craniostomy," "TICH," and "DTICH" was performed, yielding 421 articles. The secondary and tertiary searches were combined, yielding a total of 433 articles. In addition, the reference lists of selected articles were reviewed, and 24 articles were selected for critical analysis. The results of this analysis were incorporated into the review presented here. Papers primarily addressing the following topics were not included: nontraumatic lesions, patients with associated posterior fossa anomalies (e.g., Chiari malformation), posttraumatic aneurysms, chronic subdural hematomas, vertebral artery dissection, patients undergoing anticoagulation therapy, patients with associated illnesses (e.g., acquired immunodeficiency syndrome, idiopathic thrombocytopenia purpura, hemophilia, arteriovenous malformation, after craniotomy, or von Willebrand's disease), pre-CT era reports, and book chapters. In general, papers with the following characteristics were also excluded: case series with less than 10 patients evaluated by CT scan and with incomplete outcome data (mortality or Glasgow outcome score [GOS]), case reports, and operative series with operations occurring longer than 14 days from injury. Several articles with case series of less than 10 patients were examined and reviewed because of the limited number of patient series evaluating primary traumatic posterior fossa mass lesions that exist in the literature. Selected articles were evaluated for design, prognostic significance, therapeutic efficacy, and overall outcome. In addition, several articles were reviewed for the purposes of historical perspective.

Because of the rapid and life-threatening nature of neurological deterioration secondary to expanding mass lesions in the limited compartment of the posterior fossa, surgery is generally viewed as required therapy in symptomatic patients with progressive dysfunction. Because of the potential adverse consequences of withholding or delaying surgery for such patients, studies depend on retrospective analyses. As a result, there is no Class I or Class II evidence to support recommendations for the surgical management of these injuries. However, the predominantly observational studies that were reviewed yield an important and relatively clear picture of the prognosis for the patient with a posterior fossa mass lesion as patients are currently managed. Admission Glasgow Coma Scale (GCS) score5, 7, 8, 12, 24, 26 and GCS score at surgery6, 14, 19, 20, 22 correlate with outcome (GOS and mortality). D'Avella et al.5 retrospectively reviewed the clinical and radiographic characteristics of 81 patients with traumatic intracerebellar hemorrhages. Subjecting their data to multivariate analysis, they found that only GCS and the presence of concomitant supratentorial lesions independently predicted outcome at 6 months. Outcome was favorable (GOS, 4 or 5) in 95% of patients with admission GCS score of at least 8, whereas outcome was poor (GOS, 1-3) in 81% of patients with a GCS score less than 8. Class III data suggests that a neurologically deteriorating patient should undergo emergent evacuation of the mass lesion.

Neurologically intact patients with a posterior fossa lesion and no CT evidence for mass effect (compression of cisterns, distortion of 4^th ventricle, hydrocephalus) have been successfully managed nonoperatively with close observation and serial imaging1, 5, 15, 25, 28.

Wong28 conducted a retrospective study of 25 patients with posterior fossa EDH and compared clinical and radiological characteristics and outcomes between 17 patients undergoing early surgery and 8 patients managed nonoperatively. Patients with a posterior fossa EDH of at most 10 cm3 in volume, at most 15 mm in thickness, and responsible for at most a 5-mm midline shift had excellent survival rates with either surgical or nonsurgical treatment. Patients managed nonsurgically with a posterior fossa EDH greater than 10 cm3 in volume, greater than 15 mm in thickness, and responsible for greater than 5 mm of midline shift had a significantly greater mortality than those with similar CT characteristics undergoing early surgery. The disparity in mortality, however, is confounded by the strong correlation between the presence of an associated frontal lesion (which was found more commonly in the latter group) and death. This report raises the concept of conservative management for patients with posterior fossa lesions on the basis of objective CT characteristics. This concept is also supported by a two-center study performed by Bozbuga et al.1. The authors divided patients into management groups on the basis of CT characteristics. All patients (n = 14) without evidence of mass effect on CT scan, defined by obliteration of the perimesencephalic cisterns, compression and/or displacement of the fourth ventricle, or the presence of hydrocephalus, were managed nonoperatively and had a good outcome (GOS, 5). According to the authors, these objective criteria were "earlier, more predictive, and more reliable" than the clinical findings, although no statistics regarding this statement were performed. Several other case series add additional support9, 16, 25.

There are several prognostic factors that adversely affect outcome regardless of management. These include the presence of associated intracranial lesions4, 5, 12, 14, 18-22, 24, 28, extension of an infratentorial lesion into the supratentorial compartment19, the location of the lesion (e.g., intraparenchymal versus extra-axial, and midline versus hemispheric)17, 22, the presence or absence of associated hydrocephalus7, 8, 14, and the acuity of presentation, with subacute presentation portending a better outcome than acute presentation4, 14, 19, 23-25. There are no controlled studies measuring the impact of these variables on surgical versus nonsurgical management of posterior fossa mass lesions.

There are no controlled, prospective clinical trials of treatment using surgical versus nonsurgical management of posterior fossa mass lesions. The available data support rapid evacuation of posterior fossa mass lesions that 1) show CT evidence of mass effect, or 2) result in progressive neurological dysfunction. Moreover, data support expectant management with serial imaging for select cases in which there is neurological stability and no radiological evidence for mass effect.

There are several patient groups in which the distinction between surgical and conservative management is blurred. One such group includes patients who present with neurological deficit and a traumatic posterior fossa mass lesion without clinical evidence for neurological deterioration or radiological evidence for mass effect. Conversely, another group includes the neurologically intact patient with radiological evidence for mass effect from an offending hematoma. These groups have not been adequately addressed in the current literature, and, when reported, are managed at the discretion of the individual neurosurgeon, thus, precluding an accurate assessment of efficacy of treatment. The literature contains methodological problems outlined in this supplement that preclude the establishment of management standards, and even of treatment guidelines, for posterior fossa injury. Most series present prognostic data regarding outcome after either conservative or surgical treatment of posterior fossa mass lesions. In those few studies that attempt to compare outcomes, important prognostic factors known to be relevant to TBI outcome, such as cardiorespiratory instability, other systemic injuries, comorbidities, etc.2, are not controlled between the surgical and nonsurgical cohorts. As a result, we have important prognostic information regarding operatively and nonoperatively managed posterior fossa injury, but no means for valid, direct comparison between the two. This comparison is essential if we are attempting to establish a standard of care. Thus, attention needs to be directed to controlled studies of patients with similar CT and clinical characteristics who are managed with operative versus nonoperative intervention.