Sturge-Weber syndrome

Findings

Gyriform calcifications are observed over the left occipital lobe in the CT exam. The MRI demonstrates atrophy of the left cerebral hemisphere. There is enlargement of the left choroid plexus which demonstrates homogeneous enhancement post contrast. There is also gyriform enhancement post contrast most significantly on the left occipital lobe. There is diffuse enhancement of the subcutaneous tissues over the left eye.


Diagnosis: Sturge-Weber syndrome.


Key points

Classically the patients have a facial port-wine stain, ipsilateral intracranial abnormalities, contralateral hemiparesis, hemiatrophy, mental retardation, and homonymous hemianopia. The severity of these features varies widely patient to patient. Commonly the patients will have glaucoma on the affected side. Seizures are also very common.
Only 8% of patients with port-wine stains have Sturge-Weber Syndrome. 13% of Sturge-Weber syndrome patients do not have a facial angioma.
There is no clear genetic link at this time. There is no sex or race Predilection and it is very seldom seen more than once in the same family. Several different chromosomal abnormalities have been implicated.
Radiographically one can see "tram track calcifications" which are leptomeningeal calcifications like those seen on the CT image.
MRI can demonstrate the angiomatous abnormalities. In this case the cutaneous capillary angioma (port-wine stain) is well demonstrated as is the meningeal angiomatosis over the left occipital lobe. Cerebral hemiatrophy is well demonstrated by MRI as is the choroidal angiomatosis.
Multiple therapies are employed in these patients. The port-wine stains can be "removed" with laser treatments. Seizures can be treated with anticonvulsants. Refractory seizures can be treated surgically. The surgeries can be as extensive as a hemispherectomy.

Intraosseous cavernous hemangioma of the left maxillary bone

Findings

Noncontrast orbital CT demonstrates a mass arising from the left maxillary bone with internal bony trabeculations in a “honeycomb,” “sunburst,” or “spokewheel” pattern typical for an intraosseous cavernous hemangioma.
This pattern of trabeculation on CT translates into a network of linear hypointense T1 and T2 signal with interspersed areas of enhancement on the T1 post gadolinium images characteristic of this entity.


Diagnosis: Intraosseous cavernous hemangioma of the left maxillary bone


Intraosseous cavernous hemangiomas are benign neoplasms which comprise only up to 1% of all osseous tumors and 7-10% of skull tumors. These are most frequently seen in the frontal and parietal bones with the orbital and maxillofacial bones infrequently involved. These tumors are slow growing and are generally asymptomatic unless they cause mass effect on sensitive structures such as within the intraorbital compartment. In symptomatic cases, en bloc resection is generally the treatment of choice. Preoperative angiography with potential embolization may be helpful as these tumors can bleed profusely.

Clinical differential diagnosis includes fibrous dysplasia, osteoma, dermoid cyst, meningioma, eosinophilic granuloma, Lagerhan cell histiocytosis, and metastatic disease. On imaging, these tumors are well-defined and have characteristic internal trabeculations and enhancement features described as a “honeycomb,” “sunburst,” or “spokewheel” pattern. Malignant degeneration is rare.

Petrous apex chondrosarcoma

Findings

The head CT (bone windows) demonstrates a region of bony destruction extending from the right petro-occipital fissure into the carotid canal. The axial T2 images demonstrate a hyper intense, extra-axial, right petrous apex mass that extends from the petro-occipital fissure to the cavernous sinus. The margins of the mass are lobulated, and it encases the cavernous internal carotid artery. The axial T1 contrast-enhanced images demonstrate intense enhancement of the mass.


Diagnosis: Petrous apex chondrosarcoma


Key points

Classic MR imaging appearance of petrous apex chondrosarcoma is a mass located at the petro-occipital fissure with high T2 signal intensity that heterogeneously enhances.
The CT shows chondroid mineralization in 50%.
Invasive bone changes at the petro-occipital fissure strongly favors the diagnosis. Greater than 50% will have associated bone destruction.
2/3 located at the petro-occipital fissure, 1/3 located at the anterior basis sphenoid
Usually has lobulated margins
High T2 signal, low to intermediate T1 signal
Heterogeneous enhancement with contrast; whorls of enhancement within tumor matrix are often seen
Often displaces or encases the ICA
Classic presentation is a CN 6 nerve palsy. Other CN palsies can occur less commonly (3, 5, 7, 8—3, 4, and 6 are possible with cavernous sinus invasion)


Differential diagnosis
- Metastatic tumor
- Chondrosarcoma
- Plasmacytoma
- Nasopharyngeal cancer
- Chordoma
- Cholesteatoma
- Calcified meningioma
- Chondromyxoid fibroma

Distinguishing characteristics from other entities in the differential:
- Metastatic tumor – Can have a similar appearance; breast cancer and prostate cancer are two of the most common tumors to metastasize to the petrous apex
- Plasmacytoma - Usually intermediate T1 and T2 signal; usually more midline
- Chordoma - Similar appearance to chondrosarcoma but often see tumor "thumb" indenting the anterior pons; often midline
- Cholesteatoma - Does not enhance but has an otherwise similar appearance
- Calcified meningioma – Not typically destructive; low to intermediate T2 signal
- Chondromyxoid fibroma - Similar MR appearance to chondrosarcoma; areas of ground glass density can be seen on CT

Persistent trigeminal artery (PTA)

Findings

There is an aberrant artery arising from the cavernous segment of the right internal carotid artery, coursing posterior and medial to terminate in the basilar artery. The basilar artery is diminutive below the level of this vessel and is normal in caliber above it.


Differential diagnosis

Variant caroticobasilar anastomosis
- Persistent trigeminal artery (PTA)
- Persistent hypoglossal artery (PHA)
- Persistent otic artery (POA)
- Fetal origin of the posterior cerebral artery (FOPCA)


Diagnosis: Persistent trigeminal artery


Key points

Persistent right trigeminal artery (PTA) is the most common (0.1 - 0.2% of angiograms) of a group of persistent embryonal carotid-basilar artery anastomoses.
Multiple transient connections occur consecutively in fetal life between the carotid and vertebrobasilar circulations (named according to the cranial nerve they parallel):

- Proatlantal intersegmental artery – connects cervical ICA (C2-C3) to the vertebral artery between C1 and the occipital bone
- Persistent hypoglossal artery – cervical ICA (C1-C2) and proximal (caudal) basilar artery; 2nd most common
- Persistent otic artery – petrosal ICA to proximal basilar artery via the internal acoustic meatus; very rare; vertebral arteries may be absent or hypoplastic
- Persistent trigeminal artery – cavernous ICA to distal basilar; may see enlargement of the basilar above the level of this artery; supplies basilar before the vertebral and posterior communicating arteries develop.

Clinical significance: 25% prevalence of other vascular abnormalities (e.g. aneurysms)
Usually asymptomatic but may present with mass effect on adjacent structures like the pituitary and cranial nerves.
No treatment needed if asymptomatic.

Mondini malformation

Findings

Non-contrast axial CT images through the temporal bones demonstrate incomplete partitioning of the left cochlea and nonvisualization of the modiolus resulting in confluency between the middle and apical segments. Compare this to the right cochlea, which is normal. There is also abnormal dilitation of the left vestibular aqueduct.


Diagnosis: Mondini malformation


Case points

Mondini malformation occurs when there is abnormal development of the cochlea resulting in less than 2.5 turns and incomplete formation of the modiolus.
It is a cause of sensorineural hearing loss.


Discussion

Mondini malformation refers to an anomaly of the cochlea in which the modiolus fails to develop properly in the seventh week of fetal life, resulting in a cochlea with only 1.5 turns instead of the normal 2.5 turns. In addition, the interscalar septum between the middle and apical segments fails to form leading to a confluent, sac-like cochlea. There is an association with an enlarged vestibular aqueduct and anomalies of the vestibules and semicircular canals. In some cases, Mondini malformation may also be associated with Pendred Syndrome (bilateral sensorineural hearing loss and goiter)

Patients present with gradual or sudden sensorineural hearing loss with preservation of high-frequency hearing because the basal turn of the cochlea is usually preserved. These patients are also at increased risk for developing meningitis or perilymphatic fistula.

Treatment revolves around clinical presentation. Cochlear implants may be used to enhance hearing while middle ear infections are treated aggressively due to the increased risk for meningitis.

Acrania

Findings

Figure 1 and Figure 2: Coronal and axial ultrasound images of the fetal head show an absent cranial vault and an abundant amorphous mass of brain tissue. Normal cranial vault appears as bright echogenic lines characteristic of bone which is absent here.


Diagnosis: Acrania

Acrania is a rare congenital anomaly in which the flat bones of the cranial vault are partially or completely absent with complete but abnormal development of the cerebral hemispheres. The condition is identified by the absence of the calvarium. The cerebral hemispheres are surrounded by a thin membrane. The demonstration of abundant, abnormal brain tissue on the sonogram helps differentiate cases of acrania from the more common anencephaly.
Acrania is thought to occur because of abnormal migration of mesenchymal tissue, which normally covers the cerebral hemispheres. This faulty migration results in the faulty formation of the cranial bones, muscles, and dura mater. Ossification of the fetal cranium begins and accelerates after 9 weeks. The important ultrasound feature is an absent cranium, which allows diagnosis from 11 weeks onward. At 11-14 weeks gestation, the majority of cranial ossification is in the lateral aspects of the frontal bones and lower parietal bones, and no vault ossification is visible in the midline on a perfect midsagittal image. Misdiagnosis may occur if only midsagittal views of the fetus are obtained. The absence of cranial ossification may not be noted on routine examination, and the head may appear relatively normal. It is important to look specifically for frontal bone ossification in the axial and coronal planes.
The differential diagnosis includes anencephaly, large cephaloceles, hypophosphatasia and osteogenesis imperfecta. Anencephaly and acrania may commonly be confused with each other early in the pregnancy. Typically there is a progression in utero from a relatively normal appearing brain, to an amorphous brain mass, to no recognizable brain tissue which is the key to diagnosis of anencephaly in the second and third trimesters. In the first trimester, the brain of affected fetuses may appear relatively normal or may demonstrate varying degrees of distortion which can lead to confusion of accurate diagnosis. With anencephaly, the cerebral tissue is completely absent. With cephaloceles, the cranial vault can always be detected and a part of the brain is intracranial. Certain conditions such as hypophosphatasia and osteogenesis imperfecta can mimic acrania due to the lack of mineralization of the skull bones. With these conditions the intracranial anatomy is normal and the brain is surrounded by a thick layer of tissue representing soft tissues and unossified bone. Other findings such as bowing, shortening, or fractures of long bones are usually also present and aid in distinction from acrania.
Acrania is a lethal malformation. Antenatal identification allows the clinician to make appropriate and timely management decisions.

Submandibular sialadenitis

Findings

The left submandibular gland is hypervascular, inflamed and markedly enlarged (Figure 1 and Figure 2). There is dilatation of the submandibular duct leading to a calculus within the distal aspect of the duct (Figure 3 and Figure 4). There are no drainable fluid collections. There is injection and stranding of the overlying dermis (Figure 5). The right submandibular gland is unremarkable (Figure 2).


Diagnosis: Submandibular sialadenitis


Acute sialadenitis may be secondary to a bacterial/viral infection or an obstructing lesion such as a calculus or tumor at the floor of the mouth.
Associated conditions include HIV, sarcoidosis, Sjogren syndrome, dehydration, diabetes mellitus and immunocompromised/postoperative patients.
Imaging is often helpful to delineate the location of the calculus and the presence/absence of subsequent complications (abscess formation, osteomyelitis, etc).

Inflammation of the submandibular gland accounts for approximately 10-15% of cases of sialadenitis involving any of the major salivary glands. Risk factors for submandibular sialadenitis include immunocompromised/postoperative patients, debilitation, elderly patients, dehydration, diabetes mellitus, hypothyroidism, hypercalcemia, radiation/chemotherapy, eating disorders (bulimia, anorexia nervosa), and other concomitant medical problems (malignancy, head and neck infections). Associated conditions also include HIV, sarcoidosis, Sjogren syndrome, tuberculosis, mumps, and cat scratch disease. It is rare in pediatric patients.

Most commonly, acute sialadenitis is a result of a bacterial infection (common organisms include Staphylococcus aureus, Streptococcus, Haemophilus influenzae, and Pseudomonas). Less commonly, the infection may be related to a virus such as mumps, coxsackie virus, herpes and influenza. On the other hand, chronic sialadenitis is usually a result of salivary stasis, ductal stenosis, calculi or other obstructive lesions such as a tumor at the floor of the mouth. Sialolithiasis is most common in the submandibular gland, accounting for approximately 80% of cases. The majority of calculi are radio-opaque, vary in size, and can be single or multiple. Often, the calculus obstructs a duct, resulting in secondary inflammation of the affected salivary gland which then becomes suppurative.

Although plain film radiography can depict the majority of calculi, CT is often first-line imaging. The affected submandibular gland is enlarged, hypervascular and there may be associated cellulitis/myositis. Calculi are easily identified and described as being either distal (towards the ductal opening) or proximal (towards the submandibular hilum). Chronic sialdenitis manifests as a small, fatty gland.

Complications of sialadenitis include abscess formation, bacteremia/septicemia, osteomyelitis, cranial nerve involvement (facial nerve paralysis), and respiratory complications. Management of acute sialadenitis includes both medical (conservative) and surgical options. Antibiotics, analgesics, sialogogues, warm compresses, glandular massage and intravenous fluids are the mainstay of medical management. Surgical options include duct cannulation with subsequent removal of the calculus and complete gland excision.

Bilateral parotid gland MALT lymphoma in a patient with Sjögren’s and sicca syndrome

Findings

CT Neck: Enlarged and cystic change of the bilateral parotid glands and submandibular glands without discrete enhancing mass.
MR neck: Diffuse cystic replacement and enlargement of the bilateral parotid glands (and to a lesser degree submandibular glands). No discreet enhancing parotid mass identified.

Differential diagnosis
- Non-Hodgkin's lymphoma parotid
- Benign lymphoepithelial lesions – HIV (BLL-HIV)
- Sarcoid
- Warthin tumor


Diagnosis: Bilateral parotid gland MALT lymphoma in a patient with Sjögren’s and sicca syndrome.


Key Points

Sjögren's syndrome is the second most common autoimmune disease after rheumatoid arthritis.
Sjögren's syndrome is a chronic autoimmune exocrinopathy causing salivary and lacrimal gland destruction.
Clinical: Recurrent acute episodes of glandular swelling (and dry eye, mouth, skin).
CT findings: Parotid enlargement, numerous cystic lesions, +/- punctuate calcifications
MR findings: Diffuse cystic lesions (T1 hypo, T2 hyper); heterogeneous mild enhancement of nodular parenchyma and fibrosis on T1+C, with non-enhancing cysts
Appearance of cysts helps in staging: Cysts 1-2 mm suggest Stage I or II disease. Larger cysts of > 2mm suggest Stage III, IV
Stages II-IV are readily seen on parotid US
Non-Hodgkin's lymphoma frequently complicates chronic Sjögren's parotid involvement
Bilateral parotidectomy in this patient was performed for recurrent infection / intractable pain and the surgical pathology showed bilateral MALT lymphoma

Aberrant cervical thymus

Findings

Ultrasound demonstrates unique linear echogenic septa and multiple discrete echogenic foci characteristic for thymic tissue.
T1-weighted MRI demonstrates low signal intensity slightly greater than muscle.
T2-weighted MRI demonstrates high signal intensity slightly lower than that of fat but greater than muscle.
Coronal T2-weighted image identifying normal thymus in its expected location in the anterior mediastinum, as well as, the aberrant thymus in the right neck. Note that the aberrant and native thymus demonstrate the same signal characteristics on MRI.


Diagnosis: Aberrant cervical thymus

Aberrant or ectopic thymus is an uncommon entity that may be encountered in early childhood. Recognition of this entity can obviate unnecessary surgery. Aberrant and most cases of ectopic thymus do not require therapy or surgery. Ultrasound is the initial imaging modality of choice for diagnosis.
The thymus is a lymphoepithelial gland that functions in T-cell lymphopoiesis and is important for immune system development. Development usually begins in the 6th gestational week from the third and fourth pharyngeal pouches. The tissue descends along a path from the angle of the mandible to the thoracic inlet, and reaches the anterior mediastinum by the 12th week.
The thymus is typically located in the anterior mediastinum immediately posterior to the sternum and anterior to the great vessels. Each of the two lobes of the thymus is divided by primary connective tissue septa carrying blood vessels to parenchymal lobules, which are composed of a cortex and medulla, both of which are developed by the 12th week. The lobules are further divided by secondary connective tissue septa carrying blood vessels from the surface of the cortex to the corticomedullary boundary. The cortex contains only capillaries, whereas, the medulla has both small arteries and arterioles. The thymus increases in size until puberty, where it can range from 30 to 40 grams. After puberty, there is gradual fatty involution that replaces the lymphoid components.
Abnormally located thymic tissue can be categorized as being aberrant or ectopic. Patients typically present clinically with a painless, nontender mass. Aberrant thymic tissue is found along the expected normal path of descent to the anterior mediastinum from the angle of the mandible to the thoracic inlet. Aberrant thymus is commonly located in the lateral neck or in the suprasternal region, and is usually an asymptomatic, incidental finding. Ectopic thymic tissue can be found in any other location, such as the pharynx, trachea, posterior neck or mediastinum, and esophagus. Ectopic thymus can occasionally be life-threatening, such as with airway obstruction.
Ultrasound is the initial imaging modality of choice. It does not require sedation such as with MR and CT; does not involve ionizing radiation such as with CT; and does not utilize contrast media such as with MR and CT. Thymus has been found to have a characteristic and unique appearance demonstrating linear echogenic septa and multiple discrete echogenic foci throughout the gland, believed to represent connective tissue septa and their associated vasculature. The cortex of the lobules is typically hypoechoic versus the more echogenic medulla. The unique ultrasound pattern allows for easy differentiation of thymus from liver, spleen, and thyroid. In cases of thymic tissue near the mandible, one can also differentiate thymus from salivary glands (including parotid and submandibular) that are typically more homogeneous with fine internal echoes.
Occasionally MRI may be obtained for further evaluation. Normal thymic tissue in children, regardless of location, is typically homogeneously low-signal intensity on T1-weighted sequences (slightly greater than muscle) and high-signal intensity on T2-weighted sequences (slightly less or equal to fat) owing to the higher water content of the thymus. The appearance of the thymus may vary depending on age, and may also be completely or partially cystic. MRI can be useful to compare the signal characteristics of normal and abnormally positioned thymic tissue, as well as, in confirming the presence of normal thymus.
Recognition of aberrant or ectopic thymus is important because these entities usually do not require therapy or surgery, except in circumstances where there is evidence of airway obstruction. The thymus is important for immune development. Ultrasound can be used to confidently identify tissue as being of thymic origin. It is important to identify the normal thymus as well because the aberrant or ectopic thymus may be the only functioning thymic tissue within the patient. MR and/or CT may be used to supplement ultrasound findings.

Heroin induced leukoencephalopathy

Findings

Figure 1 and Figure 2: Axial T2 weighted images demonstrate diffuse high signal throughout the supratentorial white matter involving the centrum semiovale and corona radiata. There is sparing of gray matter and subcortical U-fibers. There is focal high signal in the peripheral left frontal region which corresponded to an area of acute infarct on diffusion weighted images and ADC map.
Figure 3 and Figure 4: Axial FLAIR images demonstrate diffuse high signal in the centrum semiovale and internal capsule extending to the frontal and parietal lobes with sparing of the basal ganglia and thalami. There is focal high signal in the peripheral left frontal region which corresponded to an area of acute infarct on diffusion weighted images and ADC map.


Diagnosis: Heroin induced leukoencephalopathy ("Chasing the Dragon")


“Chasing the dragon” also known as “chinesing” or “Chinese blowing” is a practice which involves inhaling the vapor of liquefied heroin. A small amount of white powder is placed on a piece of foil which is then heated from below. A stream of vapor, which looks like a dragon’s tail, arises from the molten heroin (the “dragon”) and the drug user “chases” it with a pipe or straw. This practice has gained popularity because one forgoes the risks associated with IV drug use while still benefiting from a rapid rate of absorption and onset of effect of the drug.

Heroin induced spongiform leukoencephalopathy is a progressive disease that was first described in the Netherlands in 1982. The heroin used is often impure with many additives and there is speculation that one of these additives becomes activated when heated and is the cause of the leukoencephalopathy. Since the first reported cases, many substances in the pyrolysate have been studied as potentially leading to the leukoencephalopathy but none has been positively identified. The damage is irreversible and there is no cure for this disease. Treatment is supportive care although there is a questionable benefit to using coenzyme Q and vitamin supplements.

Heroin induced leukoencephalopathy is diagnosis often made clinically and should be suspected in patients with a history of "chasing the dragon". The natural course is variable and not well defined. There may be a latent period with a subclinical evolution of white matter degeneration. Additionally, it appears that patients with higher levels of exposures have more severe disease. Patients often present in one of three clinical stages. The first stage consists of cerebellar signs (such as ataxia), apathy and motor restlessness. The second stage is comprised of tremors or myoclonus, chorea and athetosis, and pyramidal tract signs. The third stage consists of hypotonic paresis, stretching spasms, central pyrexia, akintetic mutism, and death. Progression of the disease continues even after cessation of the toxin for up to 6 months.

On pathology, there is symmetric spongiform degeneration, specifically in the cerebral and cerebellar white matter as well as the corticospinal and solitary tracts. The MR images illustrate this distribution, showing symmetric high signal on both T2-weighted and FLAIR sequences in the white matter of the cerebellum and occipital, parietal, and temporal lobes with relative frontal sparing. Specifically, there is involvement of the cerebellum and the posterior limb of the internal capsule, with sparing of the anterior limb and subcortical white matter. FLAIR images can demonstrate regions of subtle white matter abnormality more reliably and are better at excluding gray matter involvement than the T2 weighted images. There can also be additional signal abnormality in the splenium of the corpus callosum, the corticospinal tracts, and the lemniscal pathway in the brainstem. The spinothalamic tracts are spared which help to distinguish heroin induced leukoencephalopathy from other potential causes of encephalopathy. MRS in patients with heroin leukoencephalopathy has shown abnormally elevated intracerebral lactate in the affected white matter as well as decreased levels of N-acetyl aspartate in the white matter, gray matter, and cerebellum.

Guillain-Barre syndrome (GBS)

Findings

When compared with pre-contrast T1 weighted sagittal images (Figure 3), post-gadolinium sagittal T1-weighted images demonstrate enhancement and thickening of the cauda equina (Figure 4).


Guillain-Barre syndrome (GBS)


Guillain Barre syndrome (GBS) is an acute inflammatory demyelinating polyneuropathy (AIDP). It is an autoimmune disease affecting the peripheral nervous system, usually triggered by an acute infectious process. It is frequently severe and usually presents as an ascending paralysis beginning as weakness in the legs that spreads to the upper limbs and the face along with complete loss of deep tendon reflexes. Hypo- or areflexia, autonomic dysfunction and cranial nerve involvement is commonly associated. It is generally preceded by an antecedent bacterial or viral infection. Nearly 40% of patients are seropositive for Campylobacter jejuni. Diagnosis is based on clincial signs and symptoms, lumbar puncture and electrophysiologic crtieria. CSF findings include elevated protein level without pleocytosis. Nerve conduction findings suggestive of GBS include nerve conduction slowing, conduction block, prolonged distal latency, and prolonged or absent F waves. Therapeutic options include supportive measures, plasmapharesis, and immunoglobulin.
Although ascending paralysis is the most common form of spread in GBS, other variants also exist. Miller Fisher syndrome (MFS) is a rare variant of GBS and manifests as a descending paralysis, proceeding in the reverse order of the more common form of GBS. It usually affects the ocular muscles first and presents as opthalmoplegia, ataxia and areflexia. Anti-GQ1b antibodies are found in 90% of cases. Acute motor axonal neuropathy (AMAN), also known as Chinese Paralytic Syndrome, attacks motor nodes of Ranvier and is prevalent in China and Mexico. The disease can be seasonal and recovery can be rapid. Anti-GD1a antibodies are often present. Acute motor sensory neuropathy (AMSAN) is similar to AMAN but also affects sensory nerves with severe axonal damage. Recovery can be incomplete.

Radiologic studies are typically performed in order to exclude other causes. MR of the spine is performed to define infiltrative etiologies such as tranverse myelitis and compressive causes of polyradiculopathy. In cases of equivocal CSF or nerve conduction findings or atypical clinical findings, MRI of the spine can confirm or exclude the diagnosis. Findings usually include thickening and enhancement of the nerve roots that surround the medullary cone and extend along the length of the cauda equina. In GBS, there is lymphocytic and macrophagic infiltration around endoneural vessels with associated demyelination of the affected nerves. The abnormal enhancement of the intrathecal nerve roots is suggestive of blood brain barrier breakdown. Differential diagnosis of abnormal intrathecal nerve root enhancement includes AIDS-related polyradiculopathy in patients affected by CMV, arachnoiditis, sarcoidosis, and metastatic disease, The most common site of enhancement in GBS may be anterior nerve roots rather than posterior nerve roots. MRI is a sensitive but non-specific examination. Motor weakness and sensory change are correlated with patterns of nerve root enhancement and nerve conduction findings.

Acute disseminated encephalomyelitis (ADEM)

Findings

There is patchy T2 prolongation involving the thalami, basal ganglia, and scattered areas of white matter and cortex. There was no diffusion restriction or abnormal contrast enhancement.

Differential diagnosis
- Demyelinating disease (including ADEM or multiple sclerosis)
- Progressive multifocal leukoencephalopathy
- Toxic or metabolic etiologies
- Creutzfeldt-Jakob disease
- Lymphoma


Diagnosis: Acute disseminated encephalomyelitis (ADEM)


Discussion

Acute disseminated encephalomyelitis (ADEM) is an acute, monophasic demyelinating disease. It is similar to multiple sclerosis in its clinical and pathologic features. It is most commonly seen in children, but can be seen at any age. It is likely of autoimmune etiology and typically follows vaccination or viral infection. ADEM occurs most commonly from October to March. Pathogenesis likely involves T helper cells sensitized to auto antigens, such as myelin protein. Symptoms include fever, headache, and meningeal signs. Seizures, focal neurologic deficits, stupor, and coma may develop. ADEM is often clinically distinct from MS in its association with viral exposure, presence of constitutional symptoms, presence of cortical signs, and lack of posterior column abnormalities. CSF analysis is crucial to the diagnosis.

Treatment includes steroids and full recovery is possibly if treated early. Mortality was as high as 10% to 20% although this data was obtained prior to modern ICU technology.

Acute hemorrhagic leukoencephalitis is a severe variant of ADEM that is often fatal. Pathologically, there is perivascular hemorrhagic necrosis, primarily in the centrum semiovale. The major imaging feature is a rapid progression of white matter lesions over the course of a few days.


Radiologic overview of the diagnosis

CT scan is relatively insensitive, but may show scattered low density areas. T2WI and FLAIR usually show multiple regions of hyper intensity at the gray-white junction, in the brainstem, cerebellum, and basal ganglia. Optic neuritis is also common. Solid or ring enhancement can be seen. There can be variable diffusion restriction. There can be high signal on ADC maps in regions of demyelination. Spectroscopy can show low NAA. Imaging findings can lag behind clinical condition during both onset and resolution. The lesions regress with successful treatment, correlating with clinical improvement. Imaging findings are rarely pathognomonic.


Key points

ADEM is a monophasic demyelinating disease that has similarities to MS.
Imaging findings are rarely pathognomonic. CSF analysis is key to diagnosis.
MRI shows scattered areas of T2 prolongation predominantly in white matter, but may also affect gray matter.

Endolymphatic Sac Tumor

Findings

CT images showing an erosive lesion of the right petrous bone, centered at the right vestibular aqueduct opening (endolymphatic sac). The lesion is eroding the posteriolateral wall of the jugular fossa. There is also erosion of the posterior wall of the right IAC, however the right IAC itself is still intact. There are scattered bony spicules seen within the lesion.
Axial T1 and axial T2 precontrast images, respectively, at the level of cerebellopontine angle. There is a hyperintense multilobulated lesion occupying the right endolymphatic sac space. There is also a central area of low signal intensity which enhances post-gadolinium.
T1-weighted post-gadolinium axial and coronal images, respectively. There is a central area of enhancement indicating hypervascularity. Low-signal intensities within the lesion represent intratumoral bony spicules.

Differential Diagnosis:
- Paraganglioma (glomus jugulare)
- Cystic and papillary adenocarcinoma
- Chondroid lesions
- Cholesterol granuloma
- Metastasis
- Cystic schwannoma


Diagnosis: Endolymphatic Sac Tumor (Papillary Adenomatous Tumor of the Temporal Bone)


The endolymphatic sac is part of the membranous labyrinth derived from the neuroectoderm and located within the petrous portion of the temporal bone where it also contacts the dura. Endolymphatic sac tumors (ELST) were described in 1989 by Heffner as a unique pathologic entity originating from the epithelium of the endolymphatic sac, specifically the rugose or middle portion of the sac. ELST histology is benign and exhibits two patterns; mixed type and papillary adenomatous type. The former is generally confined while the latter demonstrates a more aggressive nature by locally invading the temporal bone. Patients most often present with sensorineural hearing loss and may also present with tinnitus, facial nerve palsy or vestibular dysfunction. ELST is a rare skull base lesion and most lesions are sporadic. However, there is an increased incidence seen in patients with von Hippel-Lindau disease (vHL), 7% of whom are diagnosed with this lesion. If ELST is seen bilaterally, vHL becomes a likely diagnosis.

ELST is a slow growing lesion which erodes the temporal bone and often presents with intratumoral bony spicules. In addition, due to the tumor’s slow growth, the petrous bone cortex expands and surrounds the lesion with a thin shell of reactive bone. The lesion may also exhibit hypervascularization, usually from a branch of the external carotid artery.

CT may show a soft tissue mass in the endolymphatic sac between the sigmoid sinus and internal auditory meatus. On MR imaging, this lesion exhibits a hyperintense focus on T1WI with an inhomogeneous signal on T2WI. Focal low signal intensities within the lesion represent bony fragments. Tumor foci may enhance on T1WI with gadolinium due to hypervascularity. Advanced lesions may spread far, making it difficult to identify the origin of the tumor and expanding the differential. Treatment is surgical resection.