Esthesioneuroblastoma (Olfactory neuroblastoma)

Findings

Large enhancing mass with epicenter at the level of the cribriform plate with postobstructive non-inflammatory mucosal disease. Mass invades left orbit, anterior ethmoidal air cells, medial aspect of the left maxillary sinus and frontal sinuses bilaterally. Intracranial, extradural extension with bifrontal mass effect and moderate dural enhancement. Edema or infiltration of the subcutaneous soft tissues of the frontal scalp.

Differential diagnosis:
- Esthesioneuroblastoma
- Squamous cell carcinoma of the nasal cavity
- Lymphoma
- Ewing sarcoma
- Embryonal rhabdomyosarcoma


Diagnosis: Esthesioneuroblastoma (Olfactory neuroblastoma)


Key points

Rare, highly malignant tumors composed of small round cells encircled by vascularized connective tissue.
Usually occurs in young men with second occurrence peak at ~50-60 years.
Most commonly arise superolaterally in the nasal cavity (between the middle turbinate and cribriform plate) from neuroendocrine cells within the olfactory mucosa.
Locally invasive within the nasal cavity and paranasal sinuses with frequent intraorbital and intracranial extension (squamous cell carcinoma and lymphoma often demonstrate less aggressive pattern of bony destruction).
Non-inflammatory sinusitis often accompanies disease due to obstruction.
Distant metastases in approximately 20% of cases.


Radiology

MRI:
- Hypointense to brain on T1-weighted images.
- Hyperintense to brain on T2-weighted images.
- Heavily T2-weighted images help to differentiate mass from associated obstructed sinus secretions, which usually appear brighter than the tumor.

CT: Enhancing mass with associated bony expansion and destruction.

Ruptured intracranial dermoid

Findings

Non-contrast series demonstrates multiple areas of low attenuation in the subarachnoid space (Figure 1 and Figure 2).
The second CT series demonstrates a heterogeneous, predominantly fatty lesion in the left aspect of the middle cranial fossa extending toward the orbital apex extending across the tentorial notch (3). Focus of fat is seen extending into the region of the internal audiory canal (IAC) (Figure 3).
Sagittal T1 image demonstrates multiple punctuate areas of high signal, consistent with fat droplets (Figure 4). Axial T1 post gadolinium image demonstrates a lesion with fatty and cystic components extending into the left internal auditory canal, (Figure 5). Axial T1 post gad fat sat images demonstrate the extensive fatty component, which saturates on this sequence, (Figure 6).


Diagnosis: Ruptured intracranial dermoid


Intracranial dermoids are rare, accounting for less than 1% of brain “tumors” in the US. They are more common in men than women. Unlike teratomas, they are not true neoplasms. Histologically, dermoid cysts are inclusion cysts lined by epithelium. They are caused by displaced ectodermal elements during development around the time when the neural tube closes at midline. This explains their usual near-midline location. Dermoid and epidermoid cysts are often discussed together due to their similar appearance and origin. In contrast to epidermoids, dermoids have an epithelial lining further differentiated into hair, sebaceous glands, and sweat glands. The two can be differentiated radiographically based on their typical locations and imaging characteristics. Click here for a quick comparison of the two.

Dermoid cysts are benign and slow growing, and are usually located near midline within the posterior cranial fossa, parasellar, and sub frontal areas. Symptoms depend on the size, location, and mass effect on adjacent structures. Patients may present with visual disturbances, seizures, diabetes insipidus, or headache. Intraventricular dermoids are most commonly in the fourth ventricle and rarely cause hydrocephalus. Spontaneous rupture, as in this case, can incite a chemical meningitis, resulting in recurrent headaches or seizures. Although rare, the resultant meningeal inflammation can cause vasospasm, and even stroke and death. Traumatic rupture has also been reported. In addition to intracranial involvement, dermoid cysts may also be seen in the scalp, skull, orbit, spine, nasal/oral cavity, and neck. Ovarian (abdominal) dermoids are actually well-differentiated and organized teratomas.

On CT, dermoid cysts are low attenuation, well-circumscribed, and cystic. Wall calcifications may be seen (about 20% calcify) and enhancement is rare. Fat in the subarachnoid and ventricular spaces suggests rupture, and occasionally fat/fluid levels may be seen. The resorption of subarachnoid fat is variable, and may be present up to 6 years following surgery.

On MR, dermoids typically have signal characteristics of fat – hyperintense on T1 weighted images, and hypointense on T2. Fat suppression sequences may be helpful. On both CT and MR, calcification, follicles, and debris can give dermoids a heterogeneous appearance. Dermoids are never associated with vasogenic edema, and as mentioned above, rarely cause hydrocephalus.

Treatment usually consists of complete surgical resection, depending on the size, location, and effects on local nerves and vessels. There is a risk of causing chemical meningitis during removal of the dermoid cyst if its contents spill into the subarachnoid or ventricular spaces. Recurrence is rare.

Epidermoid

Findings

Axial T1W image without contrast showed a small, rounded mass lesion in the right half of the quadrigeminal plate cistern that is minimally hyper intense to adjacent CSF. Minimal mass effect. Axial post contrast T1W shows no enhancement of the mass lesion. Axial T2W shows the same mass as the T1 image. On T2 images it is minimally hypo intense to CSF. Coronal post contrast T1W shows the lesion in the region of the quadrigeminal plate cistern. Mass is slightly hyper intense to CSF, but does not show post contrast enhancement. Diffusion weighted images show the mass to be markedly hyper intense.

Differential diagnosis:
- Epidermoid
- Arachnoid Cyst
- Parasitic infection (e.g. Cysticercosis)
- Craniopharyngioma
- Dermoid


Diagnosis: Epidermoid (presumed diagnosis)


Key points

Intracranial epidermoid represents up to 1.8% of all primary intracranial tumors. They are the most common congenital intracranial tumor. They represent the third most common CPA/IAC mass after schwannoma and meningioma.

They most commonly present with headaches and possibly with cranial nerve palsies, typically of the 5th, 7th, and 8th nerves. They may remain clinically silent for many years. There is no gender predilection. Their presentation peaks at age 40 and has a range of 20 – 60 years of age.

As the have epithelia components they grow slowly. They can cause chemical meningitis if they leak and rarely have been reported to undergo malignant transformation to squamous cell carcinoma.

Treatment involves microsurgical resection which can be complicated by encasement of surrounding structures. Recurrence is common if they are not completely resected and seeding of the subarachnoid space has been reported.


Radiology

Epidermoid typically follow CSF density and may encase surrounding structures. Most commonly they are found in the CP angle (40-50%). They can also commonly be found in the fourth ventricle and middle cranial fossa, typically para-sellar. Occasionally they can be found within the skull and spine.

CT findings: Most are hypo dense, although 10-25% will have calcifications. They typically do not show post contrast enhancement however may have minimal enhancement at the margin. There is a rare variant which may be dense secondary to hemorrhage or high protein.

MRI findings: Again they are similar to CSF on T1 and T2 pulse sequences. On T1 they are slightly hyper intense to CSF and on T2 they are isointense to slightly hyper intense to CSF. Intensity will be altered depending on the cyst contents. Minimal enhancement can be seen at the margins. They key distinguishing feature is the appearance on diffusion weighted images which is markedly intense, "light bulb bright". On ADC mapping they are isointense to brain parenchyma.

The differential diagnosis includes arachnoid cyst, which follow CSF signal on all sequences and does not show restricted diffusion. Arachnoid cysts typically displace adjacent structures whereas epidermoid lesions encase them. Cystic neoplasm's often enhance and do not follow CSF signal. Dermoid cysts are typically heterogeneous on MR and more closely follow fat signal characteristics. Additionally dermoid are typically midline. Inflammatory cysts typically enhance and have surrounding edema and/or gliosis.

Optic nerve sheath dural ectasia in neurofibromatosis type I

Findings

Figure 1: Axial contrast enhanced CT scan of the orbits reveals dilated, tortuous optic nerve sheath with no abnormal enhancement of the nerve.
Figure 2: Coronal reconstructed CT image again depicts the significant optic nerve sheath dilatation with absent enhancement.


Diagnosis: Optic nerve sheath dural ectasia in neurofibromatosis type I


The optic pathway lesions in NF-1 include glioma, meningioma, nerve sheath dural ectasia, perioptic gliosis and optic hydrops. Dural ectasia is a benign, unusual feature of NF-1 that causes nerve sheath expansion with no abnormal enhancement. The nerve can be identified separately within the dilated sheath in contrast to gliomas and meningiomas which reveal variable contrast enhancement with obliteration of the nerve itself, and homogeneous contrast enhancement around a non-enhancing nerve respectively. The differential diagnosis for optic nerve sheath dilatation includes other conditions like acute optic neuritis, intracranial hypertension and osteopetrosis, which have distinct clinical features.

While there are no pathognomonic symptoms, this entity may present with visual blurring and headaches, and rarely with proptosis and optic disc shunt vessels. Most patients have a benign clinical course and surgical intervention (nerve sheath fenestration) is reserved for patients with progressive optic nerve dysfunction. While contrast enhanced CT scan can reliably demonstrate the entity, MRI is considered the imaging modality of choice due to its high contrast resolution and multiplanar acquisition.

Benign lymphoepithelial cysts of parotid glands in HIV

Findings

Figure 1: Lateral scout image of CT scan showing the large soft tissue mass in the neck.
Figure 2 and Figure 3: Showing multiple variable sized thin walled cystic lesions in both parotid glands. Mild lymphoid hypertrophy at the base of the tongue is seen.

Differential diagnosis:
- Benign lymphoepithelial cysts of parotid glands in HIV
- Bilateral Warthin’s tumors
- Sjogren’s syndrome
- Bilateral cystic pleomorphic adenomas
- Necrotic intraparotid lymph nodes or lymphoma post-treatment
- Bilateral first branchial cleft cysts (intraparotid)


Diagnosis: Benign lymphoepithelial cysts of parotid glands in HIV


Benign lymphoepithelial cysts (BLC) of the parotid gland have been reported to occur in up to 5% of patients infected with HIV. HIV testing is recommended in patients with BLC since this can often be the initial presentation of the patient’s HIV status. A point of note is that BLC can occur before seroconversion so patients who initially test negative with BLC should be re-tested after 6-8 weeks. The exact pathogenesis of BLC is unclear but it is hypothesized that the cystic dilation and squamous metaplasia is caused by obstruction of the small intraparotid ducts by hyperplastic lymphoid tissue of the parotid lymph nodes. BLC are similar histologically to salivary duct cysts with the exception that BLC have dense lymphoid tissue within the cystic wall.

When present in patients without HIV, BLC usually presents as a unilateral cystic mass in patients in the 4th or 5th decade. In HIV positive patients the lesions are usually bilateral with associated findings of diffuse cervical lymphadenopathy and prominent adenoid and tonsillar tissue. The differential diagnosis in these patients includes bilateral Warthin’s tumors, Sjogren’s syndrome, bilateral cystic pleomorphic adenomas, necrotic intraparotid lymph nodes or lymphoma post-treatment and bilateral first branchial cleft cysts (intraparotid). BLC display characteristics of thin-walled cysts by CT and follow CSF signal characteristics on MR imaging.

The lesions of BLC are usually self-limited but surgical resection is an option in BLC for cosmetic purposes. Alternate methods of treatment include: cyst enucleation, low-dose radiation, sclerotherapy with doxycycline, antiretroviral therapy although all of these methods are associated with recurrence. There is a small risk of malignant transformation of benign lymphoepithelial cysts to lymphoma.

Developmental venous anomaly

Findings

Initial noncontrast head CT (Figure 1) shows abnormal hyperdensities within the right Sylvian fissure and adjacent insular cortex, raising the possibility of a vascular malformation.
Follow-up T2-weighted MR image (Figure 2) shows multiple linear increased signal intensity foci in the deep white matter converging near the ventricular surface. These represent dilated medullary veins of the caput medusa.
Cerebral angiography during the arterial phase (Figure 3) is normal while the venous phase (Figure 4) shows umbrella-like medullary veins converging on two collector veins (red arrows in Figure 4) which then empty into a normal venous system.


Diagnosis: Developmental venous anomaly


Developmental venous anomaly (DVA), also known as venous malformation or venous angioma, refers to aberrant venous development and is composed of a network of dilated medullary veins converging in a radial or umbrella-like fashion onto a large collector vein. The collector vein follows an aberrant course to empty into normal superficial or deep veins. A DVA can occur in the cerebrum, cerebellum, or brainstem and is characterized by normal intervening parenchyma. As it is a normal variant, clinically significant hemorrhage is unusual and should raise the possibility of a concomitant cavernous angioma or other vascular malformation.

On CT, a small DVA may not be visualized; however, a large DVA may be seen as a hyperdense lesion.

Blood flow within DVAs is slow, which produces fluid-like signal intensity rather than flow void on MR imaging. Strong contrast enhancement is typical; the lack thereof should raise doubt about the diagnosis of DVA.

On cerebral angiography, the classic “Medusa head” appearance is visualized on the venous phase, with the arterial and capillary phases normal.

Myeloma with cord compression

Findings

Sagittal T1-image (Figure 1) in a patient with multiple myeloma shows a large epidural mass in the midthoracic region with associated cord deformity. The mass displaces the epidural fat. Postsurgical changes are seen in the lower spine consistent with repair of a prior compression deformity. Marrow signal is heterogeneous throughout.
Sagittal T2 image (Figure 2) in a patient with multiple myeloma shows a large epidural mass in the mid-thoracic region with associated cord deformity. The normal CSF signal is completely displaced by the mass. Post-surgical changes are seen in the lower spine consistent with repair of a prior compression deformity. Marrow signal is heterogeneous throughout
Post-contrast T1 axial image (Figure 3) demonstrates compression of the cord anteriorly by a large epidural mass.


Diagnosis: Myeloma with cord compression


Myeloma patients with abnormal neurological findings suggesting cord compression should be evaluated by MRI when available. Imaging exam should be primarily targeted, based on the results of motor and reflex tests, rather than pain or sensory level.
Spinal cord compression is a neurological emergency that may be diagnosed by the presence of a mass lesion abutting the cord with cord deformity, or abnormal cord T2-signal.

Acute spinal cord compression is a potentially devastating neurological emergency that requires both prompt diagnosis and intervention to prevent permanent impairment. The frequency of metastatic cord compression is increasing as cancer prevalence rises and new treatment modalities prolong patient survival. Close cooperation between clinical services and diagnostic radiologists is essential for patient triage. This is especially true in cases where patients cannot be fully examined neurologically. Magnetic resonance imaging is the study of choice in evaluating these patients; it is noninvasive, does not involve radiation, and provides for investigation of both osseous and soft tissue lesions.

Many etiologies can result in acute spinal cord compression. These include trauma, infection, neoplasm, degenerative disc disease, and others. Differentiation between these various causes of acute cord compression relies on a combination of clinical history, neurological exam, and imaging findings. However, the constellation of imaging findings indicative of cord compression are similar, regardless of the causative process.

In evaluating the patient, close cooperation between clinical staff and the diagnostic radiologist is essential. Information from the neurological exam is critical for localization of the lesion and optimization of the imaging protocol. Whole spine imaging is generally undesirable as it is more time-consuming, expensive, and difficult for patients who are often in considerable pain. It further lowers resolution on exams that are often suboptimal, secondary to severe patient pain and patient movement. Spinal sensory levels on neurological examination may be up to several segments below the anatomic level of cord compression. Evaluation of motor function and reflexes is very useful for lesion localization.

There has been considerable debate within the literature on the precise radiological definition of cord compression. Animal models suggest that both direct mass effect on the cord and impingement on the epidural venous plexus contribute to pathology. Spinal cord compression may be defined as the presence of a mass lesion abutting the cord with the complete loss of intervening CSF. This must be accompanied by deformation of the spinal cord, or the presence of signal changes within the cord. The findings are best visualized on T2-weighted images. If the patient is concurrently symptomatic, acute intervention is mandated with the specific type of intervention determined by the underlying disease process.

Craniopharyngioma

Findings

There is a well-circumscribed suprasellar mass that is predominantly cystic with focal rim calcifications (Figure 1).
The pituitary gland appears normal (Figure 2). Fluid-fluid level is noted with bright signal on T1-WI (Figure 3), T2-WI and FLAIR (Figure 4 and Figure 5). Post contrast image show minimal enhancement along the periphery of the lesion with no enhancement of the lesion itself.


Diagnosis: Craniopharyngioma


Key points

Craniopharyngiomas are benign dysodontogenic epithelial tumors derived from Rathke pouch epithelium. These tumors are mostly suprasellar (75%), with intrasellar extension seen in 20% of cases.

Two types of Craniopharyngioma are classically described:
1) Childhood form- Peak 5-15 years. Has cyst formation and calcification. Has an adamantinomatous microscopic pattern and carries poor prognosis.
2) Adult form- Peaks in sixth decade. Shows papillary squamous epithelium. Symptoms are usually due to mass effect-headache, visual disturbances, behavioral changes, hydrocephalus, and endocrine dysfunction.

Craniopharyngiomas are WHO Grade I lesions. These are multilobulated, multicystic masses. The cyst may contain variations of highly proteinaceous fluid, cholesterol, and blood products.

On CT, these appear as large, lobulated heterogeneous suprasellar masses. Intrasellar extension may enlarge the sella and cause erosion of dorsum sellae. Cysts may vary in density, depending on contents. Calcification may be peripheral or irregular and nodular.

High-signal intensity within a suprasellar mass should raise suspicion of craniopharyngioma. Cyst contents are typically hyperintense on T2 and FLAIR images. Enhancement is heterogeneous in the solid portion of the tumor, with the cyst walls enhancing strongly. Cyst contents show a broad lipid spectrum on MRS (0.9 ppm to 1.5 ppm). Infiltration is common, making complete surgical resection difficult.