e,f Multifocal CNS lymphoma. Subtle right frontal and thalamic low-attenuation changes on nonen-hanced CT. T2-weighted MRI is much more sensitive and shows high signal changes in both thalami and the right inferior parietal lobe.
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acute neurologic abnormalities, particu-larly seizures. Primary glial tumors, which arise deep to the cortex, are usually much larger than metastases when they become symptomatic.
On nonenhanced CT, metastases may be iso- or hypodense to adjacent brain and are usually revealed by their surround-ing vasogenic edema rather than the mass itself. Metastases are typically hyperin-tense on T2 and FLAIR MRI and will usu-ally enhance following CT or MR contrast administration. Some are characteristi-cally hemorrhagic: choriocarcinoma, thy-roid carcinoma, melanoma, and renal cell carcinoma. These should be considered in patients with unexplained parenchymal hemorrhage, particularly at the gray-white junction. The mnemonic CT-MR (chorio-carcinoma, thyroid carcinoma, melanoma, renal cell carcinoma) can aid in their recol-lection. Lung and breast carcinoma metas-tases should be considered as well, because even though they are less likely to bleed, they are far more common (Fig. 2.34).
◆Cerebral Metastasis
Brain metastases are common in advanced malignancy and are most frequently seen in patients with lung cancer, breast cancer, melanoma, renal cell carcinoma, or gastro-intestinal adenocarcinoma. Patients often present with subacute headache, seizure, or focal neurologic impairment.
Most cerebral metastases are blood-borne, and their pattern of distribution is a consequence of regional intracerebral blood flow. Approximately 80% are found in the cerebrum, most often in the middle cerebral artery territory; 15% occur in the cerebellum, and 5% in the brainstem. Lep-tomeningeal metastases involve the sur-face of the brain and spinal cord and are the result of cortical or meningeal seeding.
Brain metastases are usually well de-marcated with pronounced surround-ing vasogenic edema. Enhancing nodules are usually less than 2 cm in diameter and located in the subcortical and corti-cal parenchyma near the gray-white mat-ter junction. Because of their juxtacortical location, even small metastases can cause
Fig. 2.34a–fa–d Parenchymal metastases from lung carcinoma. (a,b) 2-cm left frontal cortical mass with marked associated vasogenic edema. A second focus of edema involves the right frontal operculum. Minimal left-to-right subfalcine shift. The brain is otherwise normal. (c,d) T2 and FLAIR images show corresponding extensive vasogenic edema.
e,f Leptomeningeal metastases from lung carcinoma. Multiple small nodules and focal linear cortical enhancement on postcontrast CT.
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pressure, some patients’ symptoms mayimprove with therapeutic lumbar puncture,and patients in this group sometimes benefit from ventriculoperitoneal shunt placement.
Obstructive hydrocephalus, or noncom-municating hydrocephalus, refers to dila-tion of ventricles proximal to a mechanical block by tumor, blood clot, developmental web, periventricular parenchymal hemor-rhage, or other mass. The most frequent sites of obstruction are the foramina of Monro, the third ventricle, the sylvian aq-ueduct, and the fourth ventricle.
Obstructive hydrocephalus may be acute or chronic. In acute obstructive hy-drocephalus, CSF passes through small tears in the stretched ventricular ependy-mal lining and is absorbed by capillaries in the adjacent brain parenchyma (transep-endymal CSF resorption). This appears as low-attenuation parenchymal changes ad-jacent to the dilated lateral ventricles and does not occur in chronic or slowly devel-oping hydrocephalus.
Temporal horn enlargement may be the earliest manifestation of acute ventricular obstruction. The width of the third ven-tricle is a sensitive and reliable indicator of changes in ventricular volume on serial examinations (Fig. 2.35).
◆Hydrocephalus
Communicating hydrocephalus consists of enlargement of all cerebral ventricles due to impairment of CSF resorption by dural arachnoid granulations. It may be acute or chronic. Causes include trauma, subarach-noid hemorrhage, meningitis, and prior surgery. In patients with chronic commu-nicating hydrocephalus, a cause may not be identified, and patients come to clinical attention when hydrocephalus is inciden-tally discovered on studies obtained for minor trauma or in the evaluation of cog-nitive impairment.
Distinguishing between communicat-ing hydrocephalus and global cerebral atrophy may be dicult and depends on estimation of ventricular size in relation to sulcal enlargement. Generalized cere-bral atrophy may be due to chronic alcohol or anticonvulsant use, prior trauma, and neurodegenerative disorders such as Par-kinson disease, Alzheimer dementia, and long-standing multiple sclerosis.
Normal-pressure hydrocephalus is aclinical syndrome, usually seen in patientsover 50 years old, in which communicatinghydrocephalus is associated with gradualdevelopment of urinary incontinence, gaitdisturbance, and memory loss. Even thoughthese patients have a normal CSF opening
Fig. 2.35a–fa,b Chronic communicating hydrocephalus. Ventricular enlargement out of proportion to sulcal size. This appearance would be characteristic of a patient with clinical ndings of normal-pressure hydrocepha-lus or could be due to remote meningeal inammation, most often from subarachnoid hemorrhage or meningitis.
c,d Chronic obstructive hydrocephalus due to a cerebellar medulloblastoma. A hyperdense mass lls the fourth ventricle. The third and lateral ventricles are enlarged but do not show transependymal CSF resorption.
e,f Acute obstructive hydrocephalus due to craniopharyngioma. Partially calcied, solid, and cystic su-prasellar mass. Lateral ventricular enlargement; normal third ventricle and cortical sulcal eacement are due to obstruction at the foramina of Monro. Subtle low-attenuation parenchymal changes adjacent to the ventricles indicate transependymal CSF resorption.
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Head and neck conditions evaluated in the emergency department include facial trauma, blunt neck injury, orbital and peri-orbital inflammatory