Lymphoepithelial cysts in the setting of known HIV

Additional clinical history: Patient has recently tested HIV positive


Findings

Cystic replacement of the parotid glands without evidence of solid enhancing component or periglandular inflammation. Borderline enlarged Level 2 cervical lymph nodes.

Differential diagnosis:
- Treated lymphoma
- Infection / abscess including tuberculosis and atypical mycobacterium
- Brachial cleft cyst
- Abcess
- Warthin gland tumor
- Sjogren's syndrome
- Lymphoepithelial cysts


Diagnosis: Lymphoepithelial cysts in the setting of known HIV


Key points

Development of parotid gland lymphoepithelial cysts occurs early in HIV disease, often with coexistent generalized cervical lymphadenopathy. Because of this, HIV testing should be performed if a patient presents with lymphoepithelial cysts, which occur exclusively in the parotid glands. The cysts are painless and slow growing, with predominantly bilateral involvement. Lesions are usually multicystic with superficial involvement.

During embryonic development, lymph tissue is included in the parotid capsule. This lymphoid tissue is then vulnerable to the HIV virus. Patients with parotid cysts and cervical lymphadenopathy usually have CD4 levels below 500/ml. Pathogenesis of HIV related lymphoproliferative changes of the parotid remains unclear, but is likely related to an exaggerated immunological response to infection.


Radiology

CT/US/MRI: Bilateral superficial parotid cysts with possible associated adenopathy and lymphoid hyperplasia.

Pituitary apoplexy

Findings

Figure 1 and Figure 2: Non contrast CT head shows enlarged sella with a hyperdensity within it (Figure 1) with secondary thinning of bone (Figure 2).
Figure 3 and Figure 4: Coronal T1 and T2-weighted images show mass of mixed signal with isointense signal at inferior aspect and hyperintense signal at superior part, located in sellar region with suprasellar extension. Internal carotid artery on both sides show normal flow void signal.
Figure 5 and Figure 6: Sagittal T1-weighted image demonstrates the fluid level. Pituitary stalk is normal (Figure 5).


Diagnosis: Pituitary apoplexy


Pituitary apoplexy is defined as a clinical syndrome that may include headache, visual deficits, ophthalmoplegia, or altered mental status. It may occur either due to rapid expansion of an infarcted/hemorrhagic pituitary adenoma. Clinical risk factors are trauma, increased intracranial pressure, anticoagulation, bromocriptine therapy, diabetic ketoacidosis, radiation therapy, and open heart surgery. Apoplexy in pituitary adenomas may vary from 2% to 7%. Nearly 50% of apoplectic events seem to occur in patients who were not known to harbor pituitary lesion previously.

Noncontrast CT may show sellar/suprasellar mass with patchy hyperdensities. MR imaging findings may vary depending upon age of hemorrhage. Early/late subacute hemorrhage may show increased signal as seen in our case. Acute compression of the hypothalamus and/or optic chiasm may cause increase signal on T2 along the optic tracts. Presence of restricted diffusion within an adenoma may suggest an early sign of apoplexy in the form of acute hemorrhage or associated infarction.

Early diagnosis and treatment is necessary to prevent significant morbidity and mortality.

HIV vacuolar myelopathy

Findings

Figure 1 and Figure 2: Sagittal T1 and T2-weighted images of the cervical spine demonstrate minimal hypointensity on T1 with increased signal on T2 extending from C2 though approximately C5. Note the hypointensity in the vertebral bodies on both T1 and T2, a characteristic of HIV disease.
Figure 3: The axial T2 image demonstrates the abnormal signal to be symmetric within the posterior columns of the cord.

Differential diagnosis:
- HIV vacuolar myelopathy
- Subacute combined degeneration (Vitamin B-12 defeciency)
- Syphyllis (tabes dorsalis)
- Viral and post viral illness


Diagnosis: HIV vacuolar myelopathy


Vacuolar myelopathy is the common chronic myelopathy associated with HIV infection, occurring during the later stages of AIDS when lymphocyte counts are extremely low. There are usually other manifestations of AIDS at the time of diagnosis. Patients generally present with insidious progression of weakness and sensory loss with progressive spastic paraparesis in contradistinction to AIDS related CMV myelopathy. With the introduction and widespread use of HAART, vacuolar myelopathy is not as common as it once was occurring in only 10% of AIDS patients.

The histopathological findings include vacuoles and lipid-laden macrophages within the spinal cord. A hypothesis for the disease occurrence is infiltration by HIV infected mononuclear cells which secrete neurotoxic factors.

The most common imaging findings on MRI are atrophy of the cord and abnormal signal on T2 weighted sequences particularly in the posterior columns. This signal abnormality generally occurs over multiple vertebral body lengths.

The clinical and MRI findings are similar to subacute combined degeneration (myelopathy associated with Vitamin B-12 deficiency). This necessitates correlation with laboratory tests. Serum vitamin B-12 along with homocysteine and methylmalonic acid levels should be obtained. Of course in an AIDS patient, CD4 count should be obtained along with the above tests. Other causes of the imaging findings could include viral illnesses and therefore if the diagnosis is not clear, CSF analysis should be performed to identify CMV, varicella, HSV, HTLV-1 or HTLV-2. In HIV associated vacuolar myelopathy CSF and B-12 levels are most often normal.

Venous sinus thrombosis

Findings

CT head shows hyperdensity in the proximal basal veins of Rosenthal, straight sinus, and superior sagittal sinus. There is some asymmetric effacement of the perimesencephalic cistern, suggesting edema, but no significant change in adjacent parenchymal attenuation. MRI on precontrast axial TW images shows abnormal signal in the straight sinus and superior sagittal sinus. Post-contrast axial T1 weighted images show filling defects in these sinuses.


Diagnosis: Venous sinus thrombosis


Key points

Thrombosis of the cerebral venous sinuses is a difficult diagnosis to make in that presenting symptoms are quite non-specific. Venous sinus thrombosis is now thought to be much more common than before because of improved imaging techniques but is still less common than acute arterial occlusion. Venous occlusion leads to regional ischemia and infarct, most often hemorrhagic and located in the white matter or gray-white junction. Thrombosis of the deep cerebral veins may lead to bilateral thalamic hemorrhagic infarcts. The superior sagittal sinus is most commonly affected, followed by the transverse sinuses, sigmoid sinuses, and cavernous sinuses. The diagnosis should be suspected in patients with appropriate neurologic complaints and pre-disposing conditions such as hyper-coagulable states, adjacent infections (e.g. mastoiditis) or tumors, dehydration, trauma, pregnancy/post-puerpium, or oral contraceptive use. Approximately 25% of patients, however, have no identifiable pre-disposition. Presenting complaints are quite variable and may include headache, nausea, vomiting, seizures, and neurologic deficits. Mortality ranges from 10-80% and is presently more likely at the lower end of this range. Neonates, the elderly, and debilitated patients are most at risk. Systemic anti-coagulation is the standard treatment, with directed endovascular microcatheter infusion reserved for patients who progress despite adequate systemic anti-coagulation.


Radiology

MR with MR venography is the imaging modality of choice for diagnosing this condition. Ideally, on pre-contrast images, there should be loss of the normal flow void in the affected sinuses on T1 and T2 weighted images. This can vary depending on the age of the thrombus, however. Post-contrast images will show a filling defect in the affected sinuses. Flow sensitive imaging (2 D time of flight or phase contrast) is best for determining if thrombosis is indeed present. Hemorrhagic infarcts are best evaluated with gradient echo imaging sequences. Diffusion weighted images are also useful.

CT is also of use in the diagnosis of venous sinus thrombosis (as in this case). Pre-contrast CT will show hyperdensity in the affected sinuses. A classic finding is the "delta sign" in superior sagittal sinus thrombosis where a triangular hyperdensity is seen in the sinus. A "reverse delta sign" can be seen on post-contrast CT representing enhancing dura around thrombus in the sinus. Signs of infarction are classically in non-arterial distributions and can be bilateral and hemorrhagic.

Carbon monoxide poisoning

Additional clnical history: Patient sleeps in close proximity to an old furnace.


Findings

Focal bright T2 signal in the globus pallidus bilaterally.

Differential diagnosis: The focal bright T2 signal in the globus pallidus is somewhat specific for CO.

Other causes of bright T2 signal in basal ganglia/thalamus include:
- Wilson disease
- Small vessel ischemic disease (SVID)
- Creutzfeldt-Jacob disease
- Leigh disease
- Japanese encephalitis


Diagnosis: Carbon monoxide poisoning


Key points

Changes are typically seen in globus pallidus, but can occur in cerebral white matter (second most common), putamen, caudate, thalamus.

Radiology:
- Hypodense on CT
- T1W- can be normal, hypo- or hyperintense (edema or hemorrhage)
- T2W - hyperintense
- Diffusion WI - restricted diffusion

Pathologically one sees necrosis in globus pallidus with demyelination of periventricular white matter.
Presents with nonspecific symptoms of variable severity: Nausea / vomiting, headache, confusion, cognitive impairment, seizures, coma, death.
Clinically may have persistent sequelae or resolution of symptoms depending on severity and duration of exposure.
Most common cause of U.S. accidental poisoning.
Can confirm diagnosis with carboxyhemoglobin level.
Treatment: Hyperbaric O2 for acute cases.

CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoenceopalopathy)

Findings

MRI of the brain with diffusion weighted image (Figure 5), ADC map (Figure 6) and multiple FLAIR images (Figures 1, 2, 3 and 4) show marked abnormal T2 signal hyperintensity in the subcortical and deep white matter of the temporal (Figure 4) and frontal lobes (Figure 1 and Figure 2). None of the areas correlate with restricted diffusion (Figure 5 and Figure 6) or acute infarction. In Figure 3, signal hyperintensity involves the external capsules, basal ganglia and thalami bilaterally. Notably absent is abnormal decreased signal in the corpus callosum on the T1 Sagittal and none of the signal hyperintensity in the periventricular white matter is oriented perpendicularly to the lateral ventricles.

Differential diagnosis:
- CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoenceopalopathy)
- Sporadic subcortical ateriosclerotic encephalopathy (sSAE) – This is similar to CADASIL. CADASIL typically has bilateral anterior temporal and superior frontal lobe involvement which is not as commonly seen in sSAE.
- Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) – As opposed to CADASIL, areas of signal intensity associated with MELAS will frequently disappear with clinical improvement. Onset of clinical symptoms occur as early as 15 years of age and include seizures and acute stroke like symptoms.
- Hypercoagulable states (Antiphospholipid syndrome, protein S deficiency) – Differentiated by abnormal laboratory values in a young patient with multiple recurrent TIA’s/Strokes.
- Vasculitis – differentiated based on laboratory values (elevated sedimentation rate) and angiographic findings. Angiography is normal in patients with CADASIL.


Diagnosis: CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoenceopalopathy)


CADASIL, or cerebral autosomal dominant ateriopathy with subcortical infarcts and leukoenceopalopathy, is a rare (1/100,000) hereditary, non-atheromatous vasculopathy found in young adults. Patients suffer from a autosomal dominant mutation in the NOTCH3 gene, which codes for a large transmembrane receptor that is found in abnormally high concentrations on the surface of vascular smooth muscle cells. Pathologically this manifests as a non-arteriosclerotic amyloid-negative angiopathy primarily affecting perforating and meningeal arteries. Histologically, a characteristic granular osmiophilic material is found in the vascular basal membrane.

This leads to two lesion types that have been described:
- 1) Degenerated and destroyed vascular smooth muscle cells leading to impaired vasodilation in response to hypercarbia
- 2) Fibrous thickening of the arteriolar wall leading to arteriolar narrowing and compromising basal cerebral blood flow

Clinically, common presenting signs and symptoms include recurrent TIAs, cognitive deficits, migraine with aura, depression, and rarely seizures. The classic profile is that of a young adult with recurrent TIAs and a history of migraine with aura. There is no gender predilection.

Imaging findings are most characteristic with MR. T2 and FLAIR images show diffuse white matter and lacunar subcortical hyperintensities. The frontal and temporal lobes as well as the insulae are most commonly involved. Anterior temporal poles and external capsule hyperintensities carry higher diagnostic accuracy for CADASIL. The periventricular white matter and cortex are generally spared, but basal ganglia and brainstem can be involved. T1 images show both large coalescent white matter isointense lesions, as well as small well circumscribed subcortical hypointensities. Digital subtraction angiography is normal, and is done to exclude vasculitis and hypercoagulable states.

Genetic testing for NOTCH3 mutations associated with CADASIL are available. The patient had tested positive for this abnormality, and naturally had a family history of this autosomal dominant disorder.

Gray matter heterotopia and Lipoma

Findings

The lateral ventricles and 3rd ventricle are slightly increased in size. There is heterotopia along the lateral posterior aspect of the body of the L lateral ventricle. There is a posterior midline fatty lesion consistent with lipoma.


Differential diagnosis for the posterior midline findings:
- Lipoma
- Dermoid or teratoma (Should have more heterogeneity and not be as low in overall density)
- Lipomatous differentiation or transformation of neoplasm or cerebellar lipo- neurocytoma (again, more heterogeneous)

Differential diagnosis for the left lateral ventricle finding:
- Gray matter heterotopia
- Tuberous sclerosis subependymal nodules (frequently calcify and enhance)


Diagnosis: Gray matter heterotopia and Lipoma


Key points

Gray matter heterotopias:
- Are migrational disorders.
- Can result in seizures.
- Associated with many syndromes, most commonly Chiari II and agenesis of the corpus callosum.

CNS lipomas:
- Are congenital malformations and not true neoplasms.
- Are due to maldevelopment of the meninx primitive.
- Often associated with agenesis of the corpus callosum.
- About half are seen in the interhemispheric fissure.
- Many calcify, but rarely in the posterior fossa.

Posterior fossa ependymoma

Findings

Figure 1: Axial T2-weighted image shows predominantly iso-intense lobulated heterogenous mass lesion with few cystic areas located in the fourth ventricle extending into the cerebellopontine cistern through the foramen of Luschka. There is mass effect on the pons and dilatation of the fourth ventricle.
Figure 2: Axial Post Gd T1 image is showing heterogenous enhancement of the mass lesion in both intraventricular and cerebellopontine cisternal component.
Figure 3: Sagittal Post Gd T1 image showing the cranio-caudal extent of mass lesion extruding through the foramen magnum inferiorly and into the prepontine cistern. Notice the hydrocephalus with stretching of corpus callosum.


Diagnosis: Posterior fossa ependymoma


Ependymomas are common neoplasms that arise from differentiated ependymal cells that line the cerebral ventricles and central canal of the spinal cord. Ependymomas of posterior fossa have two age peaks, the first between the ages of 1 and 5 years and second in the fourth decade. In childhood, 70% of ependymomas are infratentorial and 30% are supratentorial.

Patients with posterior fossa ependymomas generally have insidious onset of symptoms with a long clinical history. Nearly all children with this tumor have nausea and vomiting resulting from increased intracranial pressure and hydrocephalus. Other symptoms may include torticollis, ataxia and lower cranial nerve neuropathies.

On MR, ependymomas are generally heterogeneous with areas of calcification, hemorrhage and cystic changes. They generally show intense enhancement but it can be variable. The most important imaging finding to identify ependymomas is extension of the tumor though the fourth ventricular outflow foramina. Tumor extending through foramen of Magendie, foramen magnum, or foramen of Luschka into the cerebellopontine angle cistern with insinuation around cranial nerves and vessels is quite characteristic.

Because of their tendency to insinuate and adhere to adjacent structures, they are quite difficult to cure. Contrary to medulloblastomas, which frequently have subarachnoid seeding at the time of presentation, ependymomas rarely have CSF spread at the time of presentation; although they may do so in few years. Although they are considered WHO grade II tumors, removal of the entire tumor is difficult and recurrence rate is high after surgery. Postoperative radiation therapy is advocated for partially resected ependymomas.

Post-traumatic carotid-cavernous fistula

History: Young man undergoing workup following trauma.
Additional clinical information: One week ago, patient was in a MVA. He has orbital discoloration and proptosis. Additional workup also reveals elevated intraocular pressure.


Findings

CT shows asymmetric increased size and density of the left cavernous sinus relative to the right side. No intraparenchymal abnormalities. Angiography shows abnormal communication between the left cavernous internal carotid (C4 segment) artery and adjacent enlarged left cavernous sinus. Immediate drainage is demonstrated via the ophthalmic veins, superior/inferior petrosal sinuses, and contralateral cavernous sinus.


Diagnosis: Post-traumatic carotid-cavernous fistula


Key points

A communication between the carotid artery and the cavernous sinus is called a carotid cavernous fistula (CCF). There are two types of CCF. A direct CCF involves the internal carotid artery and the cavernous sinus. An indirect CCF involves the dural branches of the external carotid artery and the cavernous sinus.

Carotid cavernous fistulas may be post traumatic or spontaneous in presentation. Trauma usually creates a direct CCF. Aneurysms of the cavernous ICA that rupture can cause a spontaneous direct CCF. Indirect fistulas are not usually related to trauma; rather they spontaneously develop in patients with underlying diseases such as hypertension, collagen vascular disease, or atherosclerosis.

Clinical manifestations of a direct CCF include pulsating exophthalmos, orbital bruit, motility disturbance, chemosis, and glaucoma. Vision loss will occur in 90% of patients with untreated direct CCF and 20-30% of patients with untreated indirect CCF.

Therapeutic options for a CCF include endovascular embolization of the fistula or surgery. The current method for endovascular treatment involves the use of detachable silicone balloons. A deflated balloon attached to the tip of a catheter is inserted into the cavernous sinus via the carotid artery. The balloon is slowly filled with a contrast agent until the abnormal flow of blood is no longer seen on angiography. An alternate method for endovascular treatment involves thrombosing the cavernous sinus using coils. If the endovascular rout fails to correct the CCF surgery is warranted.


Radiology

CT: Proptosis, extraoccular muscle enlargement, and enlargement of the superior ophthalmic vein may be seen. Enlargement of the cavernous sinus may be seen.
MRI: Similar findings as CT. Also, abnormal flow voids in the affected cavernous sinus may be seen.
Angiography: The most accurate way to diagnose a CCF is angiography. This allows the visualization of the fistulous communication. Immediate filling of the cavernous sinus, ophthalmic veins, and petrosal sinus occurs. If the flow is rapid through the fistula then a special maneuver may be used to slow the flow in order visualize the fistula. The Huber maneuver involves selecting the ipsilateral vertebral artery and manually compressing the ipsilateral common carotid artery. This allows slow retrograde flow of contrast into the cavernous carotid artery via the posterior communicating artery.