Interhemispheric cyst

Findings

There is agenesis of the corpus callosum. There is a multiseptated, left parasagittal midline cyst. Possible communication with the third ventricle. No associated enhancement is present. The left lateral ventricle appears dilated. No midline shift is present.

Differential diagnosis:
- Interhemispheric cyst
- Holoprosencephaly


Diagnosis: Interhemispheric cyst
At surgery: No definite communication with the ventricular system was found at surgery, thus categorizing the lesion as an interhemispheric cyst – type 2.


Key points


The association between an interhemispheric cyst and agenesis of the corpus callosum has been reported, although the etiology of the cyst is uncertain (arachnoid cyst, neuroepithelial cyst, or extensions of the ventricular lining).
Classification was most recently described by Barkovich et al based on appearance and communication with the ventricular system in 25 patients. Type 1 cysts communicate with the ventricular system while Type 2 cysts do not. Lack of communication with the ventricles was determined by visualizing a wall of the loculated cyst on MRI.

Classification of agenesis of the corpus callosum with interhemispheric cyst:
- Type 1a:
Cyst: Isointense to CSF (MR), unilocular.
Communication with lateral ventricles only.
Macrocephaly, hydrocephalus, Dandy-Walker malformation.
Males.

- Type 1b:
Cyst: Isointense to CSF (MR), unilocular.
Communication with and obstruction of third ventricle.
Macrocephaly, thalamic fusion without subcortical heterotopia.
Males > Females.

- Type 1c:
Cyst: Isointense to CSF (MR), unilocular.
Communication with lateral and third ventricles.
Microcephaly, cerebral dysplasia or hypoplasia.
Males.

- Type 2a:
Cyst: Isointense to CSF (MR), multilocular.
No communication with lateral or third ventricles.
Macrocephaly, hydrocephalus.
Male.

- Type 2b:
Cyst: Hyper attenuation (CT), hyper intense (T1W MR), multilocular.
No communication with lateral or third ventricles.
Aicardi syndrome, subependymal heterotopia, polymicrogyria, seizures, hypoplastic falx cerebri, uni- or bilateral ventriculomegaly, developmental delay.
Female.

- Type 2c:
Cyst: Isointense to CSF (MR), multilocular.
No communication with lateral or third ventricles.
Subcortical heterotopia, developmental delay.
Male.

Hallervorden Spatz disease

Findings

Figure 1 : Axial T2 weighted image at the level of the deep gray nuclei demonstrates the classic “eye of the tiger” sign, with T2 prolongation in the medial globi pallidi and hypointensity in the peripheral aspect of the globi pallidi.
Figure 2: Axial SPGR image at the same level demonstrates hypointensity in the globi pallidi as a result of the susceptibility effect from iron deposition.


Diagnosis: Hallervorden Spatz disease


Hallervorden Spatz disease is a rare neurodegenerative condition whose exact pathogenesis is unknown. Abnormal accumulation of iron in the brain, specifically in the globus pallidus and substantia nigra, is felt to play a predominant role in the neurodegeneration caused by the disease. A mutation in the pantothenate kinase gene leads to enzyme deficiency and subsequent accumulation of cysteine and iron chelates. The excess iron is deposited in the basal ganglia and damages neuronal structures.

Symptoms begin early in life, typically in early adolescence, and include extrapyramidal and gait abnormalities. Slow movements, rigid extremities, dystonia, tremors and speech abnormalities are typical findings. No cure exists, and therapy is aimed toward neurological symptoms. The typical clinical course is that of rapid progression, with death in early adulthood in most cases.

Imaging findings are usually classic, and typically described as the “eye-of-the-tiger sign”. This results from symmetric T2 prolongation in the globi pallidi with peripheral hypointensity and hypointensity in the substantia nigra. There is no associated enhancement of the areas of abnormal signal. The neural damage from abnormal iron accumulation results in diminished NAA on spectroscopy. The areas of iron deposition would be more conspicuous on susceptibility weighted images. In cases where the classic history and imaging findings do not lead to the diagnosis, other pathologies that preferentially involve the globi pallidi should be considered. These include metabolic derangements such as methylmalonic acidemia, Kearns-Sayre syndrome, Canavan disease and toxic and ischemic encephalopathies caused by anoxia, carbon monoxide and cyanide poisoning.

Branchial cleft cyst

Findings

On CT imaging, there is a well circumscribed predominantly cystic lesion at the level of the hyoid within the right neck soft tissue. The lesion has a sharp margin with the sternocleidomastoid muscle and is located superficial to the carotid artery. No adjacent stranding or inflammatory changes.
On ultrasound imaging, an anechoic structure with small amount of debris is noted within the right neck with some internal septations. No flow is noted within the lesion.

Differential diagnosis:
- Branchial cleft cyst
- Lymphangioma
- Thymic cyst
- Suppurative jugulodigastric node
- Cystic vagal schwannoma
- Cystic malignant adenopathy


Differential diagnosis considerations

Lymphangioma are multilocular, trans-spatial collections that fill the available spaces. If they are unilocular and located in typical position of second branchial cleft cyst, it may be very difficult to differentiate between the two. One characteristic that helps differentiate the two, is that lymphangiomas are infiltrative in nature while branchial cleft cysts are well defined and round.
Thymic cysts are usually located inferior within the cervical neck and are centered in the lateral visceral space.
Suppurative jugulodigastric node presents as a thick walled ovoid mass at the angle of the mandible.
Cystic vagal schwannoma has a thick, enhancing wall and is usually centered behind the carotid space causing displacement of the internal jugular vein and internal carotid artery.
Cystic malignant adenopathy presents as a necrotic mass with a thick, enhancing wall. Cystic metastasis (e.g. papillary thyroid carcinoma) and necrotic metastases (e.g. squamous cell carcinoma) as well as necrotic tuberculous lymphadenitis can have a cystic appearance similar to second branchial cleft cyst, therefore it is very important to differentiate the two and ultrasound fine needle aspiration with fluid analysis can provide useful information.


Diagnosis: Branchial cleft cyst


Discussion

The branchial apparatus is a precursor to many head and heck structures. The second branchial cleft arch overgrows the second, third, and fourth clefts and forms a cavity called the cervical sinus. During the seventh week of gestation, the cervical sinus is normally obliterated. However if there is incomplete involution, a congenital squamous epithelial lined cyst (branchial cleft cyst), sinus tract or fistulae can form. There are four subtypes of branchial cleft cyst, described below, of which greater than 90% are second branchial cleft cyst.

Classification
- Type I: anterior to the sternocleidomastoid, beneath the platysma muscle.
- Type II: adjacent to the internal carotid artery, often adherent to the internal jugular vein.
- Type III: extends between the internal and external carotid artery to the lateral pharyngeal wall.
- Type IV: lies against the lateral pharyngeal wall and may extend into the skull base.

Majority present as a painless, compressible lateral neck mass; however, they can become tender, enlarged, inflamed or develop abscesses, especially during periods of upper respiratory tract infection.

The size of cysts are variable and range from a few centimeters to > 5 cm. Most are ovoid or rounded in shape; some present with a focal rim of cyst extending to the carotid bifurcation, which presents as the "Notch sign" which is pathognomonic for second branchial cleft cyst.

These cyst can occur anywhere along the line from the tonsillar fossa to the supraclavicular region and more commonly are seen in the following areas:
- Posterolateral to submandibular gland, most are at or immediately caudal to the mandible angle.
- Lateral to carotid space.
- Anteromedial to sternocleidomastoid muscle.
- Some unusual locations for cyst include:
- Superiorly within parapharyngeal space or carotid space.
- Inferior along anterior surface of infrahyoid carotid space.
- Fistulous tract between the external and internal carotid arteries to faucial tonsil.

Treatment is usually surgical resection.

Controversy exists as to the possibility of carcinoma arising within the branchial remnant squamous epithelial lining or not. However, metastatic squamous cell carcinoma to regional lymph nodes that masquerades as branchial cleft cyst is more common.


Imaging findings

CT or MRI an easily suggest diagnosis. Contrast is used to help differentiate cystic from solid mass.

Contrast enhanced CT:
- Low density cyst with nonenhancing wall and surround soft tissue if noninfected.
- If infected, wall appears thicker and enhances with surround soft tissues appearing as dirty cellulites.

MRI:
- On T1W imaging: cyst is isointense to CSF. If cyst is recurrently infected, it may contain hyper intense contents secondary to increase protein concentration.
- T2W imaging: Hyperintense cyst, no discernible wall.
- FLAIR imaging: Cyst is iso or hyper intense to CSF.
- T1W imaging + Contrast: Peripheral wall enhancement if infected.

Ultrasound:
- Anechoic thin-walled cyst with through transmission.
- May be hyper echoic with internal debris or even pseudo-solid in appearance.
- If infected, see thickened cyst wall.

Tumefactive demyelination

Findings

Figure 1, Figure 2, Figure 3, and Figure 4 demonstrate a hypointense T1, hyperintense T2 weighted expansile mass involving the splenium of the corpus callosum. The mass has well defined borders and partially effaces the atrium (trigone) of the left lateral ventricle. There is mild patchy enhancement (Figure 4). DWI images demonstrate increased signal throughout, but only the even more hyperintense rim (Figure 5) demonstrates true restricted diffusion on ADC images (Figure 6). The remainder of the mass is increased signal on ADC images, indicating increased diffusivitiy.


Diagnosis: Tumefactive demyelination


A noncomprehensive list of lesions involving the corpus callosum includes the following: masses such as lipomas, lymphoma, glioblastoma and astrocytoma, and metastases; demyelinating diseases such as multiple sclerosis, progressive multifocal leukoencephalopathy, and Marchiafava-Bignami disease; vascular lesions such as infarctions, vascular malformations; and trauma. More focal lesions with restricted diffusion involving the splenium can also be seen in patients with epilepsy receiving antiepileptic drugs and in the setting of hypoglycemia. Narrowing the differential possibilities to a few relevant entities requires clinical history and detailed analysis of the imaging characteristics. Many of the disease processes mentioned have some unique characteristics that may help favor a particular diagnosis. However, in spite of a full clinical history and an arsenal of imaging tools, a biopsy may ultimately be necessary, as was the case with this patient.

The diagnosis in this case was tumefactive demyelination, which may be thought of as a solitary demyelinating lesion measuring greater than 2 cm and with characteristics that mimic neoplasm. Because of this, tumefactive demyelinating lesions are commonly diagnosed as such only after biopsy. Several imaging characteristics suggestive of such a lesion have been described. These include a large lesion with circumscribed borders and little or no mass effect or surrounding edema. Demyelinating lesions in general also tend to demonstrate an incomplete ring of enhancement, with the nonenhancing component facing the gray matter. The enhancing rim is felt to represent the leading edge of demyelination, and therefore usually faces the white matter. Some foci also have been shown to have decreased perfusion in some studies, which would help distinguish them from glioblastoma and lymphomas.

The abnormality in our case does illustrate a few of these characteristics, such as a circumscribed border and lack of surrounding edema. The lesion did demonstrate increased diffusivity on DWI/ADC maps, which would argue against a highly cellular tumor like lymphoma and a high grade glioma. Active foci of demyelination may demonstrate restricted diffusion. In our case, the thin peripheral rim of restricted diffusion may represent an active edge of demyelination. The mass effect on the atrium of the left lateral ventricle is a confounding factor that can be associated with tumefactive demyelination or neoplasms. Metastases usually elicit a large amount of edema which was noticeably absent in this case. Infarction is also unlikely given the patient’s age and based on the imaging characteristics of the abnormality. Infarctions involving the corpus callosum are uncommon because of the ample blood supply from the anterior and posterior circulation. Unfortunately, none of these features is specific enough to warrant watchful waiting, and therefore a biopsy was performed.

CNS fungal aspergillosis

Findings

T2 weighted intraparenchymal masses in the right temporal lobe and in the right superior frontal gyrus extending across the corpus callosum. There is ependymal enhancement of the right lateral ventricle. There is very minimal enhancement of the masses.

Differential diagnosis:
- CNS leukemia
- CNS aspergillosis
- CNS bacterial infection
- Metastasis
- Septic emboli


Diagnosis: CNS fungal aspergillosis


Key points

Aspergillosis is the 2nd most common fungal CNS infection in an immunocompromised host after cryptococcus.

Risk factors:
- Transplant recipients: renal >liver > heart.
- 1-4 months post transplant.
- Recent transplant rejection +/- retransplantation.
- Leukopenia.
- Associated with CMV infection.
- Reported nosocomial spread in some cases.
- Lung is commonest source then sinuses.


Imaging

Best finding: Multiple lesions with infarction or hemorrhage in a random distribution due to the angioinvasive nature of the infection. Hemorrhage occurs in approximately 25% of lesions.
Low signal intensity is often seen in the periphery of the lesions on T2-weighted MR images. This finding corresponds at least partially to areas of hemorrhage.
Multiple ring enhancing lesions, although more commonly there is mild/vague enhancement.
Dural enhancement with enhancement in adjacent paranasal sinus.
Mycotic aneurysms may be seen on angiography.
Locations of involvement a felt to be secondary to predilection for the lenticulostriate and thalamoperforator vessels: basal ganglia and thalamus, corpus callosum. The corpus callosum is involved in relatively few other processes (e.g., high-grade astrocytoma, cerebral lymphoma, multiple sclerosis, and Marchiafava-Bignami disease). Metastasis and pyogenic abscess do not commonly involve the corpus callosum.

Differential diagnosis in the immunocompromised patient includes
- Lymphoma
- Metastatic disease
- Septic emboli
- Multiple infarcts

Lack of enhancement may suggest the diagnosis of aspergillosis, since most brain tumors enhance. A prospective diagnosis should be suggested in the setting of early infarction and hemorrhage in the brain of an immunocompromised patient, so that antifungal therapy may be instituted.
Definitive diagnosis obtained with biopsy. Neuropathology shows invasion of blood vessels causing hemorrhagic infarction usually subcortical Meningeal infection usually focal & adjacent to infected cerebral region Angular dichotomously branching septate hyphae infiltrates tissue in centrifugal pattern. Hyphae structure tend to be found on borders of large abscesses.


Prognosis is poor with approximately 35% complete or partial response, although improved from previously 90% mortality. Treatment with Amphotericin B iv (liposomal form avoids nephrotoxicity) +/- 5 fluorocytosine often combined with itraconazole.

Reflex sympathetic dystrophy (RSD)

Findings

Three phase technetium 99m labeled MDP bone scan is shown. There is abnormal radiopharmaceutical uptake in the periarticular regions of the left hand and wrist on both immediate and delayed images.

Differential diagnosis:
- Reflex sympathetic dystrophy
- Inflammatory arthritis


Diagnosis: Reflex sympathetic dystrophy (RSD)


Key points

RSD is a poorly understood chronic abnormality of the sympathetic nervous system in a regional distribution (usually the distal extremities) that follows trauma, surgery, infection, casting, or splinting.
Clinically, it presents as severe, protracted pain in the affected limb that is out of proportion to the original injury. Additionally, there may be vasomotor disturbances. Progresses to skin and muscular atrophy.
Synonyms: Sudeck's atrophy, Complex regional pain syndrome type 1, Causalgia.

Three phases have been described:
1) Non focal pain with decreased range of motion, soft tissue edema, and increased skin temperature (lasts weeks to months)
2) Decreasing pain and skin temperature with skin thickening. Atrophy and osteoporosis may become apparent (lasts 3-6 months)
3) Continued pain with increasing atrophy and joint stiffness. Contractures may occur.

May occur in up to 5% of all injuries; most often in the upper extremity.
Typically, affects females more, often less than 50 years of age.
Plain radiographs only 60% sensitive and non-specific, showing osteoporosis of the affected limb with associated soft tissue swelling or atrophy (depending on the stage).
CT also insensitive and non-specific.
MR may show patchy bone marrow edema with stage dependent soft tissue changes.
Nuclear medicine three phase bone scan is the best study for diagnosis of RSD, showing diffuse increased uptake in the affected region on flow images; continued diffuse uptake on blood pool images, beginning to localize to periarticular regions; and continued uptake in the periarticular regions on delayed images.
Delayed images are the best for diagnosis, with a reported sensitivity of near 100%.
A "reversed" pattern of decreased relative uptake in the affected extremity may be seen on bone scan, however. This is most common, but not exclusively, in pediatric patients.
Treatment: medications (steroids, opiates, anti-epileptics, etc.); physical therapy; sympathetic nerve block; surgical sympathectomy.

Gas producing otogenic brain abscess with cerebral edema and pseudosubarachnoid hemorrhage sign

Findings

Figure 1: Soft tissue windows demonstrate generalized cerebral edema with loss of grey-white differentiation and near total obliteration of the CSF spaces. An ill-defined hypodense gas containing region is present within the left temporal lobe consistent with abscess formation. The subarachnoid spaces are hyperdense especially in the suprasellar region representing pseudosubarchnoid hemorrhage associated with cerebral edema and/or pyogenic leptomeningitis, not true hemorrhage.
Figure 2: Nondependently layering air is present within the anterior horn of the left lateral ventricle indicating communication between the left temporal lobe abscess and the left lateral ventricle and CSF spaces. On soft tissue windows, normal subcutaneous fat is seen confirming that this is intraventricular air, not fat.
Figure 3 and Figure 4: Bone windows demonstrate total opacification of the middle ear cavity and mastoid air cells consistent with otitis media and mastoiditis. There is subtle bony sclerosis and remodeling which along with the patient’s history is consistent with chronic otitis media with mastoiditis. Also note that there is no evidence of fracture to suggest penetrating trauma as an etiology for these findings. Bone window confirms the presence of air, not fat, in the frontal horn of the right lateral ventricle.


Diagnosis: Gas producing otogenic brain abscess with cerebral edema and pseudosubarachnoid hemorrhage sign


Complications of chronic supurative otitis media include (in order of decreasing frequency):
- mastoid abscess
- meningitis
- postauricular fistula
- lateral dural venous sinus thrombosis
- facial palsy
- cerebellar abscess
- Bezold’s abscess (involving sternocleidomastoid muscle)
- internal jugular vein thrombosis
- epidural abscess
- perisinus abscess
- Gradenigo’s syndrome (due to petrous apicitis)
- interhemispheric abscess
- temporal lobe abscess
- subdural abscess
- serous labyrinthitis
- Luc’s abscess (subperiosteal temporal bone without mastoiditis)

Otitic meningitis is the most common intracranial complication and can occur as a result of direct disease extension from the mastoid through a cortical defect or due to retrograde thrombophlebitis despite an intact appearance of the bone. Otogenic brain abscesses usually occur in the temporal lobe and cerebellum (2:1). Nearly all otogenic brain abscesses have underlying chronic suppurative otorrhea. More than half of all otogenic brain abscesses have an associated cholesteatoma.

Although the relative incidence of complications related to chronic otitis media is debated within the literature, many authors agree that the most dangerous complication is intracranial abscess formation which carries a 40-50% mortality rate. According to Nunez et al, 1.5 % of adults have active chronic otitis media and in an adult with active chronic otitis media, the annual risk of developing an intracranial abscess is about 1:10,000 with a male to female risk ratio of approximately 3:1. Though at first glance this risk appears relatively low, the lifetime expectancy of a 30 year old person with active chronic otitis media developing an abscess is 1:200. Intracranial complications in patients with active chronic otitis media are also more prevalent in adolescents and young adults.

Radiologic evaluation of a patient suspected of having intracranial complications related to active chronic otitis media is crucial to diagnosis and management. Axial CT with contrast is the usual modality of choice preferably with thin cuts, which can demonstrate the presence or absence of an abscess as well as details regarding its size and location. An intraparenchymal mass may show parenchymal low density with mass effect with or without an enhancing capsule. CT may be limited in the setting of acute infections. MRI may improve diagnostic accuracy, with increased sensitivity and specificity.

Etiologic agents usually include anaerobes, Proteus mirabilis, Pseudomonas aeruginosa, Streptococcus, and Staphylococcus. Anaerobic and gram negative bacteria appear to be the most common causes. Consequently, in addition to surgical management, initial treatment should include broad spectrum antibiotics with good cerebrospinal fluid penetration as well as anaerobic coverage. A team approach including an otolaryngologist, radiologist, anesthesiologist, and an infectious disease specialist among others is recommended for optimal outcome.


Pseudosubarachnoid Hemorrhage Sign

A pseudosubarachnoid hemorrhage sign is an unusual neuroradiologic finding which may be present in cases of diffuse cerebral edema and/or pyogenic leptomeningitis. In addition to increased attenuation of the otherwise normal subarachnoid spaces, the falx and tentorium can also appear dense. The etiology of this presentation is unknown. Current theories include: 1) blood-brain-barrier breakdown from microorganism toxins in pyogenic meningitis allowing leakage of dense proteinaceous material into the subarachnoid spaces; 2) cerebral edema causes displacement of CSF from the subarachnoid spaces with engorgement of the superficial pial structures creating a predominantly vascular space with relatively dense intravascular blood. Since management of the causes of subarachnoid and pseudosubarachnoid hemorrhage is quite different, it is important to be able to recognize this relatively rare sentinel neuroradiologic sign.