Clinical
Presentation: Patient is a 90-year-old woman with change in the pattern of headaches.
Imaging Findings: Non-contrast CT images show a well-defined lesion of 2x2 cm size in the floor of anterior cranial fossa and suprasellar region. The lesion has a peripheral rim of calcification, and central high attenuation. In contrast-enhanced CT, the lesion shows mild homogeneous enhancement and is seen in relation to left ACA and ICA. Pituitary gland appears normal.
Figures 1A-C: Non-contrast and contrast enhanced CT images show a well-defined lesion with peripheral rim of calcification and mild homogeneous enhancement.
Diagnosis: Calcified aneurysm
Discussion: Though the definitive diagnosis of a cerebral aneurysm is provided by angiography, large aneurysms can also be visualized on CT images. It is important to have strong suspicion for an aneurysm if a well-defined extra-axial round or lobulated hyperdense mass with or without calcification is seen in the suprasellar or parasellar locations. Aneurysm in this location can be confused with pituitary tumor, craniopharyngioma, meningioma, or sphenoidal tumor.
Aneurysms show different patterns on non-contrast CT images depending on whether they are ruptured or unruptured. Ruptured aneurysms may have high density blood in basal cisterns and sulci adjacent to them, in addition to subarachnoid hemorrhage. Unruptured aneurysms with partial or complete thrombosis appear moderately hyperdense and frequently show ring calcification of the wall or mural thrombus. In contrast-enhanced CT, partially thrombotic aneurysms have the most specific pattern showing a target configuration [1]. Completely thrombosed aneurysms may have reactive rim enhancement. Aneurysms without thrombus show strong and uniform enhancement of the patent lumen [3].
Curvilinear calcification suggests an aneurysm but is a less specific finding because it can also occur in craniopharyngiomas and sphenoidal masses. The intense enhancement of the residual lumen is relatively specific, but differentiation from other masses may be difficult on CT scans depending on the timing and degree of vascular enhancement. The MR imaging features are usually diagnostic, although they can be very subtle [2]. Significant signal heterogeneity is seen with T1 hyperintense signal due to subacute thrombus or flow related enhancement. Areas of T2 hypointensity can be seen due to intracellular deoxy or methemoglobin, calcification, or flow void. Signal misregistration artifact in the phase encoding axis due to disordered or pulsatile flow within the aneurysm is also a characteristic finding. This is not seen in other masses involving the sella. Flow related artifacts often have linear configurations [2].
Sellar enlargement, erosion, cavernous sinus invasion, and lobulated margins are reliable indicators of pituitary macroadenoma. Sellar enlargement is seen in 94 to 100% of pituitary macroadenomas, however it is a less common finding with aneurysms (8%) [2].
Hyperostosis, dense homogeneous enhancement, dural tail, isointense signal in T1 and T2-weighted images are seen in meningiomas [2,3]. Aneurysms commonly show homogeneous enhancement on CT, however the signal intensity in MRI is more heterogeneous.
Craniopharyngiomas have prominent cystic components, which can show T1 hyperintense signal due to high protein content. Although craniopharyngiomas may have significant heterogeneity, they usually have more geographical variability from a combination of cysts, cholesterol laden lakes and tumor tissue [2].
Tumors arising from the sphenoid bone include chordoma, chondrosarcoma and metastases. Sphenoidal and clival destruction is the most useful feature to differentiate these from other lesions [2].
References:
Pinto RS, Kricheff II, Butler AR, Murali R. Correlation of computed tomographic, angiographic, and neuropathological changes in giant cerebral aneurysms. Radiology. 1979 Jul;132(1):85-92. PMID: 451226 [PubMed]
Donovan JL, Nesbit GM. Distinction of masses involving the sella and suprasellar space: specificity of imaging features. AJR Am J Roentgenol. 1996 Sep;167(3):597-603. PMID: 8751659 [PubMed]
Osborn A, Salzman K, Barkovich, AJ, et al. Saccular aneurysms IN: Diagnostic Imaging, Brain. 2nd ed., Lippincott Williams & Wilkins, 2009:I-3, 12-15.
