Ocular Wegener’s granulomatosis

Findings


There is an extraconal mass within the right medial orbit, adjacent to the lamina papyracea, extending in an arc like fashion from the superomedial aspect to the inferolateral aspect of the right orbit. Mass extends into the intraconal space and splays the medial and inferior rectus muscles. Mass is hypointense to cortex on T2 weighted images and isointense to cortex on T1-weighted images. Mass demonstrates homogeneous post contrast enhancement. There is associated proptosis of the right globe. There are extensive postoperative changes of the paranasal sinuses and mucosal thickening involving all of the paranasal sinuses, predominately the ethmoid air cells.

Differential diagnosis:
- Sarcoidosis
- Lymphoma
- Vasculitis / angiitis (e.g., Wegener's granulomatosis)
- Subperiosteal abscess


Diagnosis: Ocular Wegener’s granulomatosis (favored diagnosis: the patient was known for Wegener’s granulomatosis)


Discussion

Wegener's granulomatosis is a multisystem disease classically characterized by necrotizing granulomatous inflammation of the upper and lower respiratory tract and the kidneys and necrotizing vasculitis of the small and medium sized vessels. Patients typically present between 35-55 years of age. The nose and sinuses are most commonly affected, and patients may present with sinus headaches and nasal drainage. The lungs are affected in 85% of patients, and kidneys are involved in 75% patients. Most of the morbidity of the disease is usually related to the renal component.

Wegener's involvement of the eye is not uncommon, occurring in 30-60% of cases. Approximately 8-16% of patients with Wegener's granulomatosis initially present with ophthalmic disease. Ocular manifestations can be diverse, ranging from mild conjunctivitis to episcleritis, uveitis, ciliary vessel vasculitis, and retro-orbital mass lesions. Vision loss can occur secondary to mass effect, ischemia, or vasculitis of the optic nerve or occlusion of the retinal artery.

Several medication regimens utilizing immunosuppressants are given to patients with Wegener's granulomatosis. Commonly used drugs include steroids, cyclophosphamide, azathioprine, and methotrexate.


Key radiology findings in Wegener's granulomatosis (head and neck)

Paranasal sinus inflammatory disease associated with nodular soft tissue mass in the nasal cavity.
Destructive/erosion changes of the nasal septum; nasal septum perforation is common.
Orbital invasion is the most common site of paranasal sinus disease extension.
Orbital findings can vary but may include, retro-orbital soft tissue mass resulting in compression of adjacent structures. Although rare, orbital granulomata can calcify.

Diastematomyelia

Findings

Figure 1: Myelogram of the thoracolumbar spine demonstrates a vertical linear cleft within the distal cord dividing it into two hemicords. Vertebral and rib abnormalities are noted in the lower thoracic spine.
Figure 2: Axial post myelogram CT image of the thoracic spine shows two hemicords.
Figure 3: Axial T2-weighted MR of the thoracic spine shows two hemicords.


Diagnosis: Diastematomyelia


Diastematomyelia is characterized by a sagittal division of the spinal cord into two hemicords, each with one central canal, dorsal horn, and ventral horn. An osseous or fibrous septum separates the two hemicords. The condition represents a disorder of neural tube fusion with the persistence of mesodermal tissue from the primitive neurenteric canal acting as the septum or cleft. 85% of clefts occur in the thoracolumbar spine between T9 and S1. The hemicords typically reunite above and below the cleft.

Two types of diastematomyelia have been defined:
- Type 1 diastematomyelia: each hemicord has its own dural sheath
- Type 2 diastematomyelia: both hemicords are covered by a common dural sheath

Congenital spinal deformities are seen in approximately 85% of patients with diastematomyelia. Intersegmental laminar fusion is considered virtually pathognomonic for the condition. Scoliosis, tethered cord, spinal dysraphism, and syringohydromyelia are also commonly associated.

Diastematomyelia occurs in 5% of patients with congenital scoliosis. The diagnosis is typically made in childhood, and is much more common in females. The clinical presentation varies from asymptomatic to neurologic abnormalities indistinguishable from other causes of a tethered cord. Cutaneous stigmata, most commonly a “fawn’s tail” hair patch, may indicate the level of diastematomyelia. The treatment of symptomatic patients is excision of the bony spur or septum and lysis of the adjacent adhesions.

Pneumocele of the sphenoid sinus with CSF fistula

Findings

Figure 1: Axial CT in bone windows demonstrates expansion of an air-filled right sphenoid sinus with thinned and eroded walls. Pressure erosions at the base of the right pterygoid process, medial wall of the right foramen ovale, and anterior surface of the clivus are evident.
Figure 2: Axial CT in bone windows again shows the expanded air-filled right sphenoid sinus. Note that the wall of the right carotid canal is dehisced, leaving the right internal carotid artery (ICA) completely exposed.
Figure 3: Axial CT in bone windows shows narrowing of the right superior orbital fissure by the expanded right sphenoid sinus. Again seen is complete exposure of the right ICA.
Figure 4: Reformatted coronal CT in bone windows demonstrates the expanded air-filled right sphenoid sinus eroding the base of the right pterygoid process and effacing the ipsilateral foramen rotundum.
Figure 5: Reformatted coronal CT in bone windows shows the expanded air-filled right sphenoid sinus eroding the base of the right pterygoid process and effacing the ipsilateral vidian canal.
Figure 6: Reformatted sagittal CT in bone windows shows the expanded air-filled right sphenoid sinus eroding the clivus and thinning the dorsum sellae.
Figure 7: Axial image from CT cisternogram demonstrates intrathecal contrast leaking into the expanded right sphenoid sinus along the septum.
Figure 8: Direct coronal image from CT cisternogram again shows intrathecal contrast leaking into the expanded right sphenoid sinus along the septum. (Note that the image is horizontally flipped).


Diagnosis: Pneumocele of the sphenoid sinus with CSF fistula


The term pneumocele refers to an aerated sinus that is enlarged beyond normal anatomic margins and whose walls demonstrate focal or diffuse wall thinning or erosion. Pneumosinus dilatans also describes abnormal sinus expansion but with normal wall thickness and integrity. Several past articles on this topic have used the term pneumosinus dilatans to describe an abnormally expanded sinus with or without bony erosion, favoring a single term to describe what the authors believed to be variations of the same entity. We prefer to distinguish between the two entities based on the presence or absence of bony wall thinning or erosion. Nevertheless, both of these lesions can occur in any sinus, but the maxillary sinus is most commonly involved by pneumoceles, whereas the frontal sinus is most commonly affected by pneumosinus dilatans. In contrast, pneumocele of the sphenoid sinus is a rare lesion.

Pneumoceles may occur suddenly, presumably by a trap-valve mechanism or by rupture of a large mucocele. In contrast, pneumosinus dilatans tend to develop chronically. However, the etiology and pathogenesis of pneumosinus dilatans are still poorly understood. Proposed theories of sinus hyperpneumatization include infection with gas-forming microorganisms, hormonal influences, and congenital defects. Pneumosinus dilatans are usually incidental findings, but have been associated with various disorders including but not limited to fibrous-osseous dysplasia, Klippel-Trenaunay, hydrocephalus and arachnoid cysts. Pneumosinus dilatans of the sphenoid sinus may also be the first sign of a meningioma of the planum sphenoidale or tuberculum sellae.

The clinical severity of symptoms depends upon the sinus or sinuses involved and will guide patient management. Reported manifestations of pneumoceles, and similarly of pneumosinus dilatans, include but are not limited to headaches, frontal bossing, exophthalmos, vision loss, and CSF rhinorrhea. Based on the presumed etiology of a trap-valve mechanism, the surgical treatment of pneumoceles includes opening the affected sinus directly into the nasal cavity via transnasal endoscopic approach. In our case of sphenoid pneumocele with associated CSF fistula, the sphenoid sinus was packed with subcutaneous abdominal fat using transnasal endoscopic technique.

HIV encephalitis

Findings

Mild parenchymal volume loss with symmetric nonenhancing periventricular and subcortical white matter T2 prolongation. No mass effect.

Differential diagnosis:
- Microvascular disease
- HIV encephalitis
- PML
- Toxo/lymphoma
- Chemotherapy/Radiation
- Leukodystrophy
- Demyelination – MS, ADEM


Diagnosis: HIV encephalitis (known HIV infection).


Key Points: HIV Encephalitis / AIDS Dementia complex

Cognitive disturbances that progress to dementia
7-27% of AIDS patients
Direct CNS infection by HIV +/- CMV
MR imaging primarily shows central volume loss and diffuse or periventricular white matter disease (both demyelination and gliosis)
Can be difficult to differentiate from PML
Pre-HAART (Highly Active Antiretroviral Therapy) prognosis was poor, but HAART therapy is felt to decrease incidence and induce remission.

Cerebral amyloid angiopathy (CAA)

Findings

MRI of the brain without contrast shows diffuse cortical atrophy as well as multiple small (< 5 mm) cortical-subcortical foci of decreased signal intensity, best seen in GRE sequences (Figure 7 and Figure 8). Some of these focal areas of low signal intensity are not seen or are barely discernible on T2-weighted sequences (Figure 3 and Figure 4), and not seen at all on T1-weighted (Figure 1 and Figure 2) or FLAIR sequences (Figure 5 and Figure 6). No areas of abnormal signal intensity are seen in the basal ganglia. In addition, areas of increased white matter signal intensity, compatible with leukoencephalopathy, are best seen on FLAIR sequences (Figure 5 and Figure 6).


Diagnosis: Cerebral amyloid angiopathy (CAA)


Cerebral amyloid angiopathy (CAA) is a significant cause of cortical-subcortical cerebral bleeds in the normotensive elderly individual. In CAA, beta-amyloid protein is deposited in the media and adventitia of small to medium sized blood vessels in a cortical, subcortical, and leptomeningeal distribution. These deposits are associated with fibrinoid necrosis, vessel wall fragmentation, and microaneurysms, all of which produce vascular fragility and lead to spontaneous micro and/or macrohemorrhages, with the latter sometimes having devastating consequences. Fibrinoid necrosis can also lead to blood vessel narrowing and subsequent distal ischemia. CAA is sometimes called Congophilic amyloid angiopathy, because beta-amyloid deposits are highlighted with Congo red stain and show yellow-green birefringence under polarized light.

CAA has been found at autopsy in up to one third of individuals between 60 and 70 years old, and in up to two thirds 90 years and older. Nevertheless, the majority of patients with CAA remain asymptomatic, and thus the condition is currently under recognized. When symptoms do arise, they are similar to those of a transient ischemic attack or dementia, which are nonspecific findings making CAA difficult to diagnose clinically. Patient symptomatology is usually related to macrohemorrhages, defined as larger then 5mm, and can resemble an acute ICH. CAA is not associated with systemic amyloidosis, yet is strongly associated with Alzheimer disease.

Radiographic findings of CAA normally include cortical and subcortical hemorrhages, atrophy, and leukoencephalopathy. Microhemorrhages associated with CAA are normally not seen on CT, T1-weighted, or T2-weighted sequences. Therefore, if CAA is suspected clinically, or in the event that cortical-subcortical focal intracranial hemorrhages are seen on a noncontrast enhanced CT, an MRI should be obtained, which includes T2*-weighted gradient-echo (GRE) sequences. At present, GRE is one of the most sensitive sequences for the detection of acute and chronic hemorrhages, like the ones associated with CAA. The hemosiderin present within these cerebral hemorrhages, causes local magnetic field inhomogeneities, with a prominent loss of signal on T2*-weighted GRE sequences. Susceptibility-weighted imaging (SWI) is another sequence that is gaining acceptance, which is also very sensitive in detecting cerebral microhemorrhages. Nevertheless, for a definitive diagnosis of CAA, biopsy or autopsy is required. It is important to note that patients taking anticoagulants or aspirin which are diagnosed with CAA, should be counseled regarding the risks and benefits of treatment. Finally, no treatment is currently available to halt or reverse beta-amyloid protein deposition associated with CAA.

Nasal dermoid sinus with cyst

Findings

CT show a hyper dense mass within the lower anterior interhemispheric fissure. MR confirms the extra-axial mass within interhemispheric fissure. The mass is isointense on T1, hyper intense on T2 and does not exhibit restricted effusion. There is a tract identified extending from the bridge of the nose to the lesion, best seen on sagittal images. Mild peripheral enhancement of the lesion is noted following the administration of intravenous contrast.

Differential diagnosis for extra-axial mass in the interhemispheric fissure:
- Nasal dermal sinus with epidermoid/dermoid
- Fatty marrow in cristi galli
- Nasofrontal cephalocele
- Meningioma

Findings are most compatible with a nasal dermal sinus tract with a cyst within the interhemispheric fissure. The mass is felt to be more compatible with a cyst rather than a dermoid or epidermoid because it does not have signal characteristics of fat as seen with with a dermoid, or exhibit increased signal intensity on diffusion like an epidermoid. There is no evidence surrounding edema.


Diagnosis: Nasal dermoid sinus with cyst (presumed diagnosis).


Key points

Nasal dermoid sinus is a result of defective embryology of the anterior neuropore resulting in any combination of sinus tract with epidermoid/dermoid.
Typical presentation is a young child with pit on the skin of nasal bridge.
Other clues to the diagnosis is a bifid cristi galli and enlarged foramen cecum.
Predisposes to recurrent meningitis if left untreated.
Treatment is surgical excision.

Odontogenic keratocyst

Findings

Multiple CT axial views of the mandible show a well corticated expansile cystic lesion with somewhat scalloped borders containing a comminuted pathologic fracture.
Figure 1: Comminuted pathologic fracture of an expansile lesion with well defined margins in the left mandible.
Figure 2: Soft tissue density likely secondary to protein/blood products.


Diagnosis: Odontogenic keratocyst


Odontogenic keratocysts also known as primordial cysts arises from remnants of dental lamina and make up 10% of jaw cysts. They occur more commonly in the 2nd to 4th decades and have a 2:1 M:F predilection.

75% are located in the posterior mandible around the 3rd molar. The most common maxillary location is the canine region. 50% are lucent, unilocular with well-defined sclerotic margins. Many cysts are expansile and multilocular.

The pathology demonstrates remnants of dental lamina. They are comprised of a fibrous wall lined by squamous epithelium with a low protein content. The cysts could have a low attenuation on CT likely due to low protein content or a high attenuation from hemorrhage. Theses cysts make up 10% of jaw cysts and are associated with Noonan and Marfan syndrome. A minority of odontogenic keratocysts are multiple and 50% of these cases will have associated basal cell nevus.

Approximately 50% of patients are symptomatic with jaw swelling being the most common symptom, seen in up to 85% of symptomatic patient. Other signs and symptoms include sinus tract with drainage seen in 15%, pain, paresthesia and trismus.

The natural history of odontogenic keratocysts are rapid growth with high recurrence rate. Treatment is with enucleation and aggressive curettage. Due to high recurrence rate follow up studies are recommended.

CNS dermoid

Findings

Along the posterior aspect of the midbrain there is exophytic focus of hyper intense T1 and heterogeneously hyper intense T2 signal which is heterogeneously hypo intense on T2 with fat suppression. This small mass heterogeneously enhances on T1.

Differential diagnosis:
- Dermoid
- Lipoma


Diagnosis: CNS dermoid.


Key points: Inclusion tumors (epidermoid and dermoid)

Congenital tumors resulting from abnormal incorporation of ectodermal elements during neural tube closure
Benign
Not neoplastic
Slow-growing
1% of intracranial tumors
Epidermoid 7x more common than dermoid


Epidermoid (cholesteatoma)
- Histopathology: Squamous epithelium, keratin, cholesterol
- No fat or calcification
- Cystic lesion filled with accumulating desquamated epithelium and cholesterol
- Typically conforms to enclosing space and surrounds structures
- Occasionally has mass-effect
- Less complex and thinner wall than dermoid
- Rupture is rare
- Location—off midline, most commonly at CPA (cerebellopontine angle)
- Imaging:
No contrast enhancement
Follows CSF on CT and MR but bright on FLAIR and diffusion
Differential diagnosis: arachnoid cyst


Dermoid
- Histopathology: Epidermoid + hair, fat, and sweat glands, calcification common, with arc-like calcification in 20%
- Contains ectoderm + dermal appendages (hair, sebaceous/sweat glands/secretions, desquamated keratinized epithelium)
- Predominantly fatty
- More complex and thicker wall than epidermoid
- Associated with dermal sinus tracts
- Rupture
Into subarachnoid space
Causes serious, potentially fatal, chemical meningitis (with vasospasm)
Larger lesions have higher rupture rate
- Location—midline, most commonly in spinal canal
- Imaging
Enhances if infected and especially with meningitis following rupture
Mimics fat on CT and MR with heterogeneity secondary to soft tissue
Differential diagnosis: lipoma

Crossed Cerebellar Diaschisis (CCD)

Findings

CT: Post-craniotomy surgical changes with vasogenic edema extending from left frontal lobe into left parietal and temporal lobes. There is symmetric cerebellar atrophy without evidence of asymmetric right hemispheric volume loss.
PET/CT: Decreased metabolism in left frontal lobe and right cerebellar hemisphere representing crossed cerebellar diaschisis.
MR: Enhancement throughout much of the remaining left frontal lobe, with extension into the right frontal lobe, basal ganglia, and the genu of the corpus callosum.
MRI: While PET/CT and MRI findings were suggestive of radiation necrosis, tissue biopsy showed evidence of recurrent malignant oligoastrocytoma (WHO grade 3). Cerebral lesion was subsequently resected surgically.


Diagnosis: Crossed Cerebellar Diaschisis (CCD) in a patient with radiation necrosis and recurrent malignant oligoastrocytoma (WHO grade 3)


Crossed cerebellar diaschisis (CCD) is a functional reduction in the cerebellar hemisphere contralateral to a cerebral lesion. It has been observed following strokes, intracranial tumors, epilepsy, and various types of intracranial trauma. There is a direct relationship between the incidence of CCD and increasing lesion size. CCD can range from a potentially reversible finding (typically following an acute stroke) to permanent degeneration. While most frequently associated with frontal lobe pathology, CCD can also be present with lesions involving the thalamus, basal ganglia, and the internal capsule. The cerebropontocerebellar pathway is thought to be the etiology of CCD; its interruption leading to a reduction in oxygen metabolism and glucose uptake in the contralateral cerebellar hemisphere that can be demonstrated with PET imaging. Conventional CT and MRI studies often do not show any abnormalities, as diaschisis does not always produce structural alterations.

Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct

Findings

Brain MR demonstrates abnormal signal intensity in the right pons on FLAIR and restricted diffusion of the right pons. MR angiography and CT angiography demonstrate a small 3 mm aneurysm at the origin of the right superior cerebellar artery. At the time of embolization three days later, the aneurysm had significantly grown in size. It was successfully embolized.


Diagnosis: Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct (the patient had known bacterial endocarditis, presumably caused by an untreated infected wisdom tooth)


Discussion

A mycotic or infectious aneurysm is caused by bacterial infection of a vessel resulting in a rapidly growing aneurysm. These are usually located at branch points of vessels. Atherosclerotic aneurysms, conversely, do not have such rapid growth. Infectious aneurysms are usually associated with bacterial endocarditis. Primary infectious aneurysms have an unidentified source. Secondary infectious aneurysms arise from a specific source of infection, like bacterial endocarditis or tuberculosis.

Bacterial aneurysms are usually saccular and have associated thinning of the vessel wall and perivascular inflammation. They are caused by septic emboli which infarct the vasa vasorum, causing necrosis of the vessel wall and development of a pseudoaneurysm. Mycotic aneurysms can demonstrate arterial stenosis near the aneurysm, multiple aneurysms, and rapid changes in morphology.

High mortality, around 70%.

Endovascular treatment can involve either parent artery occlusion or coiling of the aneurysm. For this patient, the coiling of aneurysms of the superior cerebellar artery can have complications of ischemia of the cerebellar cortex if the superior cerebellar artery is occluded. However, there is usually collateral vascular flow from the AICA and PICA through the vermian arcade. Aneurysmal coiling should include not only the parent vessel, but also include any tiny vessels that near the aneurysm that are feeding the aneurysm wall, to prevent refilling of the aneurysm with blood. Tight packing of a mycotic aneurysm could lead to rupture since the wall is very fragile, therefore, concomitant occlusion of the parent vessel should be considered.