Chapter VI./3.: Radiological aspects of cerebral metastasis

Kinga Karlinger

VI./3.1.: Introduction

Cerebral metastases account for 15% of intracranial tumors, which is 40% according to other authors (in adult population).

Very characteristically more than 90% of all cerebral metastasis derives from six types of tumors. Therefore, in case of a cerebral metastasis of unknown origin, these tumors should be taken into account principally. Conversely, if a patient has such type of tumor, it is likely that a cerebral metastasis develops.

Since half of this >90% derives from bronchial carcinoma, in case of a cerebral metastasis of unknown origin, bronchial carcinoma should be suspected first. This fact is supported further by the fact that this type of tumor gives so-called „early metastasis” most characteristically. Accordingly, symptoms of metastasis advert our attention to the tumor search. Sometimes traditional imaging modalities (chest radiograph, chest CT) cannot find bronchial carcinoma. By this time, biopsy taken from the cerebral tumor gets ready and refers to an origin of bronchial carcinoma. Frequently the primary tumor cannot be found even by targeted search neither by PET (undersized, <5 mm). Even in the course of the autopsy the primary tumor can be remained hidden in spite of the conscious search. Malignant melanoma is very malignant and gives metastasis almost everywhere (in „unusual” places as well), cerebral metastasis develops quickly. In contrast, in case of e.g. ovarian carcinoma, even if metastatisation is extensive, cerebral metastasis is rare.

Primary tumors causing cerebral metastasis:

• 1. bronchial carcinoma (rarely squamous cell)

• 2. breast cancer

• 3. melanoma

• 4. gastrointestinal tumors: colon, rectum

• 5. clear cell renal cancer (hypernephroma)

• 6. choriocarcinoma

• 7. head and neck tumors can extend into the skull by direct perineural way / directly

Sarcoma metastasis is extremely rare in the cerebrum.

In childhood:

• 1. leukemia / lymphoma gives deposition

• 2. sarcomas (especially osteogeneous)

• 3. Wilms tumor

• 4. germinal cell tumors

• 5. neuroblastoma

Localisation of metastases is characteristic – according to location of the „obstruction” of tumor cells.

1. 1. corticomedullary boundary (bronchial carcinoma metastatizes into the parenchyma)

2. 2. in subarachnoid space: carcinomatous meningiosis (leptomeningeal spread is characteristic of leukemia and lymphoma, prostatic carcinoma gives dural metastasis for choice)

3. 3. subependymal spread is most characteristic of breast cancer

4. 4. metastasis can develop in cranial bones

5. 5. direct perineural spread

6. 6. Pituitary gland (stalk) can be also a target of metastasis (especially breast cancer)

Certain metastases have particular morphologic characteristics according to the nature of primary tumor as well on the basis of which their origin can be likewise referred.

Cystic transition can be observed in metastases of pulmonary squamous cell carcinoma and pulmonary adenocarcinoma, and metastases of renal cell cancer can be primarily cystic as well.

Calcification is characteristic of certain carcinoma metastases as well as of primary tumors:

Mucin producing carcinomas are such, in addition, bone and cartilage producing sarcomas.

• Calcification can be observed following radiotherapy.

• Characteristically, bleedings develop in certain tumors.

• Among these, malignant melanoma is the most common.

• Second one is the choriocarcinoma.

• Small cell lung cancer (oat cell)

• Renal cell cancer

• Thyroid tumor

• Bronchial cancer

These metastases are hyperdense already on unenhanced CT scan and their remarkable contrast enhancement indicates their hypervascularisation.

On CT /MRI imaging, following localisational/behavioral forms can be found characteristically of metastases:

If multiple lesions can be observed on a cerebral CT/MR scan (principally in adults and elderly age), metastasis should be considered, since two-third of metastases is already multiple at the moment of detection (metastases of RCC, pelvic and abdominal tumors often are single, whilst e.g. metastases of melanoma and lung are multiple). It must be noted that not all multicentric cerebral tumors have a distant organic origin: metastasis of a central nervous system tumor also occurs. Tumors can extend from one side to the other one e.g. in commissural way: corpus callosum, internal capsule, massa intermedia.

Spread can be through liquor: towards the ventricles and subarachnoid cisterns. Satellite metastases can occur. There are multicentric central nervous system tumors as well, sucj as e.g. the relatively rare multicentric gliomas. Coincidental, synchronous cerebal tumors can also occur of other and other histological origin. Multicentric meningeomas also befalls. It is systemic in neurofibromatosis but multinodular meningeomas are also possible aside from them. Primary central nervous system lymphoma is also multicentric.

More than half of metastases is located in the hemispheres, which is followed by the cerebellum and the brain stem. Metastases of RCC, pelvic and abdominal tumors often are infratentorial.

Metastases are usually surrounded by edema, but is must be admitted that perifocal edema is not always present and even a tiny metastasis can develop a very large edematous region.

The chapter structure

• VI./3.1.: Introduction

• VI./3.2.: Computed tomography – CT

• VI./3.3.: Magnetic resonance imaging – MR

• VI./3.4.: Take home messages

References