mercoledì 23 febbraio 2011

Lateral medullary syndrome (Wallenberg syndrome)


Axial FLAIR (Figure 1 and Figure 2) and T2-weighted (Figure 3 and Figure 4) images demonstrate mild signal hyperintensity in region of the left lateral and posterior medulla PICA territory.
Axial DWI (Figure 5 and Figure 6) and matching ADC maps (Figure 7 and Figure 8) demonstrate true restricted diffusion in the left lateral and posterior medulla PICA suggestive of cytotoxic edema fort an acute infarction.
3D TOF posterior circulation MIP projection (Figure 9) demonstrates absence of a normal left PICA. It's possibile to see the right PICA for comparison, arising from the distal right intracranial vertebral artery. There is also a mild narrowing of the basilar artery. It's possibile also to appreciate bith the superior cerebellar arteries.

Diagnosis: Lateral medullary syndrome (Wallenberg syndrome)

Adolf Wallenberg (November 10, 1862-1949) was a German internist and neurologist who first described the clinical manifestations (1895) and the autopsy findings (1901) in occlusions of the arteria cerebelli posterior inferior (Wallenberg syndrome).

Lateral medullary syndrome is characterized by sensory deficits affecting the trunk and extremities on the opposite side of the infarct and sensory, and motor deficits affecting the face and cranial nerves on the same side with the infarct. Other clinical symptoms and findings include ataxia, facial pain, vertigo, nystagmus, diplopia, Horner syndrome, and dysphagia. The cause of this syndrome is secondary to occlusion of the PICA near its origin. Similar symptoms may be produced by vertebral artery occlusion near the origin of the PICA.

Afflicted persons can have dysphagia resulting from involvement of the nucleus ambiguus and slurred speech (dysphonia and dysarthria). Damage to the spinal trigeminal nucleus causes absence of pain on the ipsilateral side of the face as well as an absent corneal reflex. The spinothalamic tract can be damaged, resulting in loss of pain and temperature sensation to the opposite side of the body. Damage to the cerebellum can cause ataxia. Damage to the hypothalamospinal fibers disrupts sympathetic nervous system relay and gives symptoms analogous to Horner syndrome (ptosis, anhidrosis, and miosis).

In older patients, the most common cause of posterior circulation ischemia is thromboembolic disease resulting from accelerated atheromatous disease or embolic disease from a cardiac source. In young patients with posterior fossa ischemia, in addition to embolic disease, the diagnosis of arterial dissection should also be considered.
Wallenberg syndrome synonyms: dorsolateral medullary syndrome, lateral bulbar syndrome, lateral medullary infarction syndrome, and PICA syndrome.

martedì 8 febbraio 2011

Subdural empyema


A large left middle cranial fossa subdural empyema is demonstrated, with a relatively thin rim of enhancement. Internally, there is a large quantity of debris. There is mass effect, with a modest midline shift and effacement of the left lateral ventricle. Inflammatory changes are demonstrated in the left temporal bone which is likely the source of the abscess. There is diffusion restriction, not marked, consistent with abscess. There is extensive dural enhancement, along with considerable surrounding edema.

Differential diagnosis:
- Subdural empyema
- Chronic subdural hematoma
- Subdural effusion
- Subdural hygroma
- Dural metastasis

Diagnosis: Large left middle cranial fossa subdural empyema; left mastoiditis

Key points

Loculated collection of pus in subdural space
Best diagnostic clue: Extra-axial collection with contrast enhancing rim
Supratentorial typical
Infratentorial (up to 10%), often associated with mastoiditis
Crescentic typical; may be lens shaped on coronal images
CT demonstrates extra-axial collection, iso-to hyper dense to CSF on noncontrasted CT; shows strong peripheral enhancement with contrast
Best imaging tool: MR with DWI to demonstrate presence, nature, extent and complications
T1W image shows:
Extra-axial collection hyper intense to CSF
Crescentic extra-axial collection
T2WI demonstrates a lesion that is Iso-to hyper intense to CSF,
FLAIR shows a crescentic fluid collection which is hyper intense to CSF, underlying brain may be hyper intense
DWI shows restricted diffusion (increased signal intensity); Differentiates subdural empyema from subdural effusions
T1WI post contrast shows:
Prominent enhancement at margin related to granulomatous tissue and inflammation
Encapsulating membranes enhance strongly, may be loculated with internal fibrous strands
May see enhancement of adjacent brain parenchyma
MRV may show venous thrombosis seen as a lack of flow
CT may miss small collections
Complications include cerebritis and brain abscess, cortical vein and dural sinus thrombosis, and cerebral edema
Subdural empyema is much more common than epidural empyema
In older children, adults: Related to paranasal sinus disease (>2/3), in infants and young children it can be a complication of bacterial meningitis
Most common signs/symptoms include fever, headaches, meningismus, sinusitis, cerebritis
Sinus or ear infection in > 75% of cases
Confused with meningitis which may lead to delayed diagnosis
Can occur at any age
Rare, yet high mortality rate.
If subdural or epidural abscess is discovered, look also for sinusitis, otomastoiditis, dural sinus thrombosis and brain abscess
Progresses rapidly, neurosurgical emergency
Surgical drainage via wide craniotomy is gold standard