Extra-axial posterior fossa lesions simulating intra-axial lesions on computed tomography

Giant aneurysm of distal posterior inferior cerebellar artery: a case report and review of the literature

INTRODUCTION

Aneurysms in the vertebrobasilar system are rare and in the distal segment of the posterior inferior cerebellar artery they are even less frequent. Giant aneurysms are also rare in the posterior cranial fossa. Giant aneurysms of the distal posterior inferior cerebellar artery generally can have mainly compressive effects on the adjacent structures and they can be mistaken for tumors.

CASE PRESENTATION

We report the case of a 74-year-old Italian woman who presented with a complaint of dizziness. Her dizziness was found to be a result of aneurysmal dilatation arising from the distal segment of the right posterior inferior cerebellar artery. A mid-line suboccipital craniotomy was performed, and the aneurysm was clipped without post-operative deficits and with improvement in the patient's dizziness. In our present report, we also review the literature and discuss our case with regard to the clinical and radiological features and surgical procedure performed.

CONCLUSION

To the best of our knowledge, few cases of this type of aneurysm have been described in the literature. Our patient had a good outcome after surgical treatment.

Distal posterior inferior cerebellar artery aneurysms: clinical features and management

OBJECT

Aneurysms located on the distal portion of the posterior inferior cerebellar artery (PICA) are uncommon, and their underlying pathology, natural history, and clinical management are poorly understood. To clarify these lesions more fully, the authors undertook a retrospective analysis of the clinical features and management results of 22 distal PICA aneurysms in 20 consecutive patients treated at one institution by the same surgeon during the past decade.

METHODS

The series included 10 men and 10 women (mean age at presentation 51 years). Nine patients presented with only subarachnoid and/or intraventricular hemorrhage (median Hunt and Hess Grade II). In seven patients intracerebellar hemorrhage was also found; two patients presented with pressure effects and two hemorrhages were incidentally discovered. Prominent comorbidities included cigarette smoking (50%) and hypertension (50%). The 13 saccular and nine fusiform distal PICA aneurysms were distributed on the following segments of the PICA: lateral medullary (seven lesions), tonsillomedullary (five lesions), telovelotonsillar (five lesions), and cortical (five lesions). Six oases were associated with cerebellar arteriovenous malformations. Skull-base and far-lateral transcondylar surgical approaches were used to secure the aneurysms in 86% of cases, either by direct clipping (13 lesions), vessel sacrifice (four lesions), or vessel sacrifice plus bypass (two lesions). Two aneurysms were treated using endovascular PICA ablation. Overall outcome at hospital discharge was excellent or good in 70% of cases. At long-term follow up (100% of patients, mean 123 days), an excellent or good outcome had been achieved in 85% of cases.

CONCLUSIONS

Depending on the PICA segment that was affected, variations in clipping strategies and surgical exposures aimed at the PICA branch and main trunk preservation were major contributors to good long-term results.

Growth of totally thrombosed giant aneurysm within the posterior cranial fossa. Diagnostic and therapeutic considerations

We report a case in which growth of a totally thrombosed giant aneurysm of the posterior cranial fossa was demonstrated by computed tomography (CT) scans repeated after 4 years. A magnetic resonance (MR) image demonstrated an onion-skin-like, laminated structure within a calcified wall. The laminated structure had developed around an old thrombosis, without any communication to the flowing blood. It showed intensities indicating recent clots, revealing that the giant aneurysm had grown by recurrent intramural hemorrhage rather than by intraluminal accumulation of thrombotic materials. This case illustrates that totally thrombosed giant aneurysms still have the potential of growth.

The glossopharyngeal neurinoma. Case reports and literature review

Glossopharyngeal neurinomas are rare entities. Only 16 cases have been described so far in the literature. Our experience with 2 cases demonstrates the non-specific and discrete clinical presentation of the ninth nerve neurinoma, but illustrates also some typical radiological aspects, enabling a more precise preoperative diagnosis. Two cases are presented and a survey of the literature is given.

The diagnosis of solitary primary reticulum cell sarcoma of the posterior fossa with computed tomography

The CT findings in two surgically and histologically verified cases of primary reticulum cell sarcoma of the cerebellar hemisphere with secondary involvement of the cerebellopontine angle are presented. It is suggested that a correct diagnosis is possible by CT if the following criteria are present: 1. slightly increased attenuation of the mass on the precontrast scan; 2. mottled appearance of the definitely enhancing mass; 3. ill-defined borders on both the pre- and postcontrast scans; 4. degree of mass effect less than that expected from the size of the lesion; 5. involvement of the cerebellopontine angle without signs indicating an extra-axial origin of the tumor. These criteria reflect the gross and microscopic neuropathological features of the tumor.

Computed tomography in the diagnosis of brain stem gliomas

Twenty patients with brain stem gliomas were diagnosed by CT. The diagnosis was established on the basis of characteristic appearance, density pattern and mass effect. Differentiation from brain stem metastasis or angioma is frequently possible based on CT findings.