INTRODUCTION
Cerebral angiography in the evaluation of cranioencephalic tumours has a role that is de- termined to a great extent by CT and MRI as it is no longer required to diagnose the existence of a lesion (7). However, selective cerebral an- giography is still utilized in cases where the neurosurgeon is considering emergency surgery or another aggressive form of treatment.
Modern angiography is very different from the past, as the evolution in cauterization mate- rials and angiographic equipment have brought about vast improvements in the quality of the images obtained while drastically reducing pa- tient risk. The innovations in equipment have witnessed the introduction of digital acquisi- tion, storage and image display, thereby making the resulting examination yet more practical to perform and review (1-4, 6, 8).
The evolution of the imaging instrumenta- tion has coincided with the enormous techni- cal progress made in angiographic materials, such as increasingly small catheters with ever greater torsion control and thin walls with ex- tremely high mechanical resistance. It there- fore follows that what was once considered a procedure associated with some degree of risk has now become quite safe, benefiting from
the use of new contrast media, appliances and instruments.
Neovascular architecture is characterized by certain semeiological signs deriving from tradi- tional angiography, including: alteration of the calibre, morphology and course of the vessels;
presence of haemodynamic alterations; the presence of arteriovenous microshunts; and presence of a characteristic arteriolar-capillary parenchymal blush. There are three possible subtypes of angioarchitectural alteration in neoplasia: typical pathological vascularization (e.g., meningiomas, gliomas); atypical patho- logical vascularisation and avascular lesions (5).
Pathological vascularization can originate from the intraaxial vasculature (e.g., internal carotid and vertebrobasilar artery branches) or the meningeal vessels (e.g., branches of the ex- ternal carotid artery). The type of vasculariza- tion depends on tumour type, however it should be stressed that angiography, like all other imaging techniques, is not able to provide a precise tissue diagnosis.
The table below shows a general classifica- tion of brain tumours as published by the WHO:
– Neuroectodermal tumours (gliomas, medul- loblastomas, ependymomas, papillomas, neu- rinomas)
3.3
ANGIOGRAPHY IN BRAIN TUMOURS
C. Piana, U. Pasquini
– Ectodermal tumours (craniopharyngiomas, hypophyseal adenomas)
– Embryogenic tumours (epidermoids, der- moids, teratomas)
– Mesodermal tumours (meningiomas, an- giomas, fibromas, chordomas, lipomas, os- teomas, sarcomas).
This angiographic discussion of brain tu- mours cannot exhaustively deal with all the var- ious types that can occur and will only detail the most frequently encountered.
MENINGIOMAS Semeiotics
Statistically, meningiomas are most frequent in females, with a ratio of 3:1 as compared to males. With regard to other intracranial neo- plasias, they are the most common type with an overall relative incidence that varies between 20-25%.
The angiographic characteristics of menin- giomas vary with the histological type and spe- cific degree of vascularization. Minor distinc- tions are made between skull base menin- giomas and those of the convexity. Menin- giomas have preferential sites with frontal, pte- rional and parietal locations being the most common, and they can be multiple.
During their development meningiomas de- form and compress the overlying neural and vascular tissues, some of which, such as the in- ternal carotid artery and cranial nerves within the cavernous sinuses, become enveloped with-
Fig. 3.17 - Meningioma of the left pterion. The imaging studies reveal a left frontoparietal homogenously enhancing, broad dural based mass with perilesional oedema and neovascularity originating from the left middle meningeal artery. [a) unen- hanced CT; b, c) left external carotid, left middle meningeal ar- teriogram].
a c
b
in the confines of the tumour. They are supplied by arterial branches that are usually hyper- trophic. These tumors demonstrate a patholog- ical circulation fed principally from meningeal vessels that are usually quite regular with a dif-
fuse and homogeneous tumour blush in the lat- er phases of the serial angiographic study (Figs 3.17, 3.18). The neovascular tumour circulation can also be supplied from the pial arteries (i.e., internal carotid or vertebrobasilar arteries).
Fig. 3.18 - Invasive left frontal region meningioma. The skull x-ray demonstrates a large osteolytic lesion of the left frontal region. The CT shows a hyperdense lesion invading the overlying skull and extracranial soft tissues. The angiogram of the left external carotid ar- tery reveals prominent neovascularity originating from branches of the left superficial temporal and middle meningeal arteries.
[a) frontal radiograph; b), c) axial CT imaged with bone and soft tissue windows; d) left external carotid arteriogram].
a c
b d
In order to obtain a precise and complete documentation of the vascular contributions to the meningioma, it is mandatory to perform an angiographic examination that also includes all the meningeal arteries that might potentially contribute to this supply. Angiographic exami- nations must also include a thorough search for venous alterations (e.g., compressions and dur- al venous sinus invasion with stenosis or com- plete occlusion).
The circulation of meningeal sarcomas is quite different than that of benign menin- giomas and is characterized by reduced circula- tion times, in part due to the presence of arteri- ovenous fistulae. Given their site of origin in the meninges, these tumours are also supplied by intra- and extracranial meningeal branches.
Olfactory groove (Fig. 3.19) and cavernous venous sinus meningiomas are less frequent and have typical appearances on CT and MRI.
In the case of olfactory groove meningiomas, angiographic examinations rarely contribute additional information. However, in the case of cavernous venous sinus meningiomas, an- giography can show an encasement and re- sulting stenosis of the carotid siphon and a neovascularization with parenchymal blush originating directly from branches of the carotid siphon itself. This observation points out the potential danger of surgical interven- tion and in some cases may suggest alternative treatment (radiotherapy).
One last characteristic location that bears discussion is the meningioma of the tentorium cerebelli. In such cases the angiographic pic- ture is typical as it shows one or more hyper- trophic tentorial meningeal arteries originating from the supraclinoid segment of the internal carotid that flow toward the central core of the tumour, where the characteristic hypervascular- ization is noted.
Discussion
From these brief considerations it would ap- pear evident that the angiographic examination of a meningeal lesion must be performed not so much for diagnostic purposes, but rather to ob-
tain an accurate angiographic map of the lesion and surrounding tissues. There are two funda- mental reasons to accurately define this map: to demonstrate the type and degree of vascular- ization and to show the neurosurgeon the ves- sels that are to be isolated and coagulated.
Technological progress in recent years has brought about a new approach to the treatment of meningiomas: embolization. This technique
Fig. 3.19 - Olfactory groove meningioma. The right internal carotid arteriogram demonstrates neovascularity associated with a persistent parenchymal blush within a lesion in the ante- rior aspect of the skull base on the right side originating prin- cipally from ethmoid arterial branches. In addition, the right ophthalmic artery in hypertrophied as a result of the increased flow in transit to the neoplasm. [a) frontal projection right in- ternal carotid arteriogram; b) lateral projection right internal carotid arteriogram].
a
b
typically precedes surgery, as it results in a devascularization of the tumour permitting a considerable reduction in the surgical time pe- riod, a reduction in intraoperative bleeding and therefore an overall reduction in surgical risk and complications. However, the embolic pro- cedure must be performed by an expert team trained specifically in interventional radiology.
GLIOMAS Semeiotics
CT and MRI have altered the indications for cerebral angiography somewhat by permitting a precise determination of the location of the lesion as well as a clear depiction of its various components and gross internal structure. How- ever, visualization of the pathological neocircu- lation of the tumor still remains the province of conventional angiography.
On angiographic examinations gliomas have direct and indirect signs: direct signs are the ac- tual vasculature of the neoplasm and the indi- rect signs are shifts of the vascular structures surrounding the tumour induced by its growth.
This distinction between direct and indirect signs derives from conventional angiographic semeiology.
These direct angiographic signs are charac- terized by the specific afferent and efferent ves- sels, the appearance of the tumour vessels and the circulation time of the tumour. The evalua- tion of the efferent vessels is also quite impor- tant in the diagnostic angiographic analysis of brain tumours; for example, the detection of medullary veins and deep venous drainage vir- tually excludes the possibility of an extraaxial lesion.
The regularity of tumour neovessels can be an element in favour of the relative benignancy of a lesion. Conversely, the irregularity of the vessels is usually associated with malignancy, and the presence of arteriovenous shunts al- most always indicates a malignant lesion.
Another distinctive characteristic of brain tumours is the tumour circulation time: in a number of lesions this circulation time is re-
duced due to the presence of arteriovenous shunts with early venous drainage. In other le- sions the tumour circulation time appears in- creased and the tumour blush persists within the lesion. Tumour circulation times are also in- fluenced by the presence of associated perile- sional oedema, the presence or absence of vas- cular spasm and the degree of resistance of the draining veins (e.g., compression or complete obstruction of the draining venous structures).
Glioblastomas (Figs. 3.20, 3.21) are the sub- type of glioma that has the most varied angio- graphic findings. In part due to their high bio- logical activity, theses tumours typically reveal angiographic characteristics that define a ma- lignant pathological circulation: a reduction in
Fig. 3.20 - Left temporoparietal glioblastoma multiforme. An- giogram of the left internal carotid artery reveals a prominent parenchymal blush and arteriovenous shunting typical of ma- lignant cerebral neoplasms.
circulation time, irregularity in the calibre of vessels with very disorderly patterns, arteriove- nous fistulae and early venous drainage.
Other gliomas have different angiographic findings, some presenting with a picture that is more or less avascular. Even some quite hyper- vascular gliomas have areas that are avascular indicating necrosis or the presence of cysts or haemorrhage within the tumour.
Benign astrocytomas (Fig. 3.22) and oligo- dendrogliomas only rarely have significant macroscopic pathological neocirculation. How- ever, in certain cases some intrinsic vascular el- ements can be detected. When present, such findings can be interpreted as a greater or less- er degree of lesion malignancy.
OTHER CEREBRAL NEOPLASMS
Ependymomas and medulloblastomas can demonstrate a minor neovascularization; how- ever, these are not characteristic elements that define these lesions. In choroid plexus papillo- mas (Fig. 3.23), the angiographic findings show a neocirculation composed of small vessels that give rise to a dense tumour blush. In these le- sions one observes hypertrophy of the choroidal arteries from which the tumour ves- sels originate.
Fig. 3.21 - Left temporal lobe cystic glioblastoma. Angiogram of the left internal carotid artery shows mass effect in the ele- vation of the Sylvian vessels associated with a peripheral parenchymal blush.
Fig. 3.22 - Right parietal lobe astrocytoma. Contrast enhanced CT shows mural enhancement within a right parietal lobe sub- cortical mass lesion surrounded by much perilesional oedema.
The angiogram of the right internal carotid artery demonstrates no hypervascularity. [a) axial CT following IV contrast; b) lat- eral projection right internal carotid arteriogram]
b
a
Discussion
The angiographic analysis of cranial neoplasia is important from the view point of the potential neurosurgical therapeutic implications. Emer- gency angiographic examinations implicate the intention to perform interventional procedures in order to reduce the vascularity of the lesion and are dictated by the patient’s clinical situation.
The exact representation of the tumour vas- cularity permits a proper and careful approach
c
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e a
b
Fig. 3.23 - Papilloma of the right choroid plexus. The contrast enhanced CT shows a homogeneously enhancing intraventric- ular mass. The right internal carotid arteriogram reveals a mass lesion having neovascularity, associated with a tumor blush and arteriovenous shunting. [a) axial CT following IV contrast; b, e) frontal projection right internal carotid arteriogram; c, d) lat- eral projection right internal carotid artery arteriogram].
to stereotaxic biopsy, as it shows the course of the vessels to be avoided and tumour vessels.
These observations potentially reduce the risks of a possible intratumoral haemorrhage.
Complete angiographic examinations facili- tate surgical intervention. However, in cases in which the lesion cannot be operated on, angiog- raphy may suggest alternative therapies such as radiotherapy and intraarterial chemotherapy.
This latter technique is proving efficacious in the treatment of particularly hypervascular le- sions; in such cases, the angiographic picture can be correlated with considerable biological activity, and therefore with greater pharmaco- logical sensitivity.
Lastly, in cases where the neurosurgeon does not intend to intervene, angiographic evalua- tions are of little or no value as the combination of CT and MRI provide more than satisfactory information concerning the type and location of the lesion.
METASTASES
Given precise clinical and historical medical data, this type of lesion is usually not difficult to interpret using CT and MRI. From a statistical point of view, autopsy findings reveal brain metastases in 24% of patients suffering from tumours. The tumours that most frequently spread to the CNS include melanomas, lung carcinoma, breast carcinoma, thyroid tumours and leukaemia/lymphoma.
Although there is usually no diagnostic dilemma in diagnosing cerebral metastases on CT and MRI in the presence of multiple le- sions, this changes in the case of isolated lesions that are often cortical-subcortical in location and may infiltrate the overlying meninges. In such cases, it may be necessary to perform an angiography in order to resolve differential di- agnostic problems between metastasis and meningioma.
The angiographic picture of metastases (Fig. 3.24) is somewhat typical with the depic- tion of rather homogeneous neovascularity, which is most frequently supplied by a single arterial branch. This neovascular circulation
Fig. 3.24 - Right temporoparietal parenchymal metastatic neo- plastic disease. Contrast enhanced coronal CT demonstrates an enhancing mass lesion adjacent to the skull on the right side.
The right internal carotid arteriogram in the lateral projection reveals an intensely hypervascular cortical lesion associated with a tumor blush and arteriovenous shunting. [a) coronal CT following IV contrast; b, c) lateral projection right internal carotid arteriogram].
a
b
c
has well-defined margins and persists in time into the venous angiographic phase. Typically a single draining cortical vein is visible.
The lesion usually has a cortical or subcorti- cal location. In cases where the lesion infiltrates the overlying meninges and bone of the skull, an examination of the meningeal branches is es- sential as the absence of supply of the tumour from these vessels permits differentiation from meningioma.
Discussion
This brief analysis highlights the fact that multiple metastases do not necessarily require an angiographic evaluation, as CT and MRI are sufficient for diagnosis. The principal excep- tion is that of isolated cortical lesions that infil- trate the overlying meninges and skull. As not- ed above, angiography can provide valuable in- formation in such cases in terms of differentiat- ing a metastasis from a meningioma.
CONCLUSIONS
Cerebral angiography has precise indica- tions in the light of new diagnostic and thera- peutic considerations; presurgical angiographic investigations are always required in order to facilitate the surgical approach to the lesion by demonstrating the afferent and efferent vascu- lar branches to the lesion. Angiographic studies may prove useful in subsequent intraarterial embolization or chemotherapy in conjunction with surgery or once it has been established that surgery is not possible.
Cerebral angiography is considered super- fluous in the more benign or lower grade tu- mour types, in tumours of the posterior cranial
fossa and in tumour follow-up; in most of these cases, CT and MRI are usually sufficient for di- agnosis and treatment planning.
MRA has a complementary diagnostic role regarding information on hypervascular in- tracranial lesions. In particular, the recently developed techniques involving the injection of a contrast medium bolus in order to better identify the arterial vascularization may prove useful in the future. This makes it possible to visualize some degree of the pathological neo- vascularization present in many malignant tu- mours. However, bolus contrast enhanced MRA does not yet possess the sufficient defini- tion to distinguish with certainty the smaller arteries; in addition, by its nature it lacks the ability to selectively differentiate the various vascular territories.
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