Band heterotopia

CASE 1 (7-month-old)






CASE 2 (Pre-adolescent)






Findings

Case 1: Axial and coronal T2-weighted images of the brain in a 7-month-old girl with seizures demonstrate a band of isointense signal within the subcortical white matter, characteristic of band heterotopia.
Case 2: Axial and coronal T1-weighted images demonstrate band heterotopia, better seen in this preadolescent girl due to completion of myelination.


Diagnosis: Band heterotopia


Band heterotopia is a rare neuronal migration anomaly which manifests as homogenous bands of gray matter are interposed between the lateral ventricles and cortical mantle with normal appearing white matter on either side. The overlying cortex may be normal, pachygyric, or display a simplified gyral pattern with short gyri and shallow sulci. At least six morphologically distinct subtypes have been described. Band heterotopias represent a subset of gray matter heterotopia which also includes subependymal and subcortical heterotopia subtypes.

Band heterotopia typically affects female patients as a result of an X-linked dominant inheritance pattern secondary to abnormal function of the doublecortin (DCX) gene (Xp22.3-p23) or less frequently the LIS1 (17p13.3) gene. Male patients can be affected due to sporadic mutations of these genes (41 reported cases in the literature by D’Agostino, et al in 2002). The rate of detectable mutations involving DCX or LIS1 in male patients (42%) is lower than the rate of 85% described in female patients. Dysmorphic features described in patients with band heterotopia include microcephaly (most common), wide nasal bridge, high arched palate, and short stature.

The clinical presentation of band heterotopia can range from normal to nearly normal intelligence and mild developmental delay to frank mental retardation. Seizures are often also present and may begin in the first decade, ranging from partial to generalized or multiple seizure types. The discovery of the underlying brain malformation is due to the onset of seizures in 65% of patients. Eventually 95% of patients with band heterotopias will develop epilepsy. Seizures associated with band heterotopia are often refractory to medical therapy, and surgical therapies such as callosotomy may be performed in these patients. In the series of 30 male patients published in 2002, 46% of patients were refractory to medical therapy and experienced up to 20-30 seizures daily despite trails of multiple therapeutic regimens. Affected male patients tend to have either mild or severe symptoms, whereas, female patients tend to have symptoms within the mild to moderate range of the spectrum from minimal cognitive impairment to severe mental retardation. Posterior involvement, in particular the partial posterior and intermediate posterior subtypes, occur more commonly in male patients. Frontal and diffuse subtypes are more often present in affected female patients.

Capillary Telangiectasia

Findings

There is an ill-defined enhancing focus in the medial right temporal lobe on post gadolinium contrast T1-weighted imaging (Figure 4). There is no corresponding signal abnormality or mass on the precontrast T1-weighted, T2-weighted, or FLAIR images (Figure 1, Figure 2, and Figure 3, respectively). There is no mass effect. On susceptibility-weighted imaging (SWI) the lesion shows hypointensity (Figure 5).


Diagnosis: Capillary Telangiectasia


Brain capillary telangiectasias are benign vascular malformations which are often found incidentally.
They can be visualized by gadolinium contrast and gradient-echo susceptibility or susceptibility weighted imaging, but not through catheter angiography, and may often not be visible on conventional T1/T2, FLAIR, or diffusion-weighted imaging.
Often asymptomatic and usually no treatment is required.

Brain capillary telangiectasias (BCTs) are one of four major types of vascular malformations which occur in the brain (the other three are arteriovenous malformations, cavernous malformations (cavernous angiomas), and developmental venous anomalies (venous angiomas), and represent up to 20% of all intracranial vascular lesions. BCTs consist of multiple ectatic capillaries surrounded by normal brain parenchyma and are usually devoid of calcification, gliosis, extraluminal hemorrhage, and hemosiderin-laden macrophages. BCTs are most common in the midbrain, pons, medulla, and spinal cord, but they are found throughout the central nervous system. Multiple BCTs are possible, especially in certain syndromes (e.g.; ataxia telangiectasia, Osler-Weber-Rendu, or Sturge-Weber syndrome).

Often found incidentally, BCTs are usually benign, small in size, and rarely grow over time. They are rarely symptomatic and are not associated with any particular clinical feature but have been reported to be associated with headache, vertigo, and tinnitus.

BCTs are relatively well visualized through susceptibility weighted imaging where they demonstrate marked signal intensity loss due to deoxyhemoglobin present in slow flowing blood. They are also well visualized through gadolinium-enhanced T1-weighted imaging sequences where they are seen as small faint lesions. BCTs are difficult to visualize through conventional T1/T2, FLAIR, or diffusion-weighted imaging and are considered to be one of the “angiographically occult vascular malformations” due to their small size, tendency to occlude, and sluggish flow.

Ewing sarcoma of the occipital bone

Findings

Figure 1: Unenhanced CT shows a heterogeneous attenuation mass with cystic spaces in the posterior fossa.
Figure 2: Intense enhancement is noted after contrast administration.
Figure 3: Bone window section showing permeative destruction of the left occipital bone.
Figure 4: Axial T1 weighted image showing extra- axial mass with multiple cystic spaces.
Figure 5: Coronal T2 image showing the extra-axial origin clearly with mass effect on the cerebellum. The cystic spaces appear hyperintense.
Figure 6: Axial T1 weighted image showing intense enhancement of the mass.


Diagnosis: Ewing sarcoma of the occipital bone


Ewing sarcoma is a small round-cell tumor arising from mesenchymal cells. These tumors affect children and young adults in the age group of 5-15 years. The long bones, flat bones like the scapula and the vertebrae are the most common sites. Primary Ewing sarcoma affecting the calvarium is extremely rare, making just 1% of the cases. In the skull, the tumor more often arises from the frontal and parietal bones and less common locations include ethmoid, temporal and occipital bones.

CT scans (bone window) reveal poorly marginated permeative destructive lesion involving both inner and outer tables of the skull. The "onion peel" appearance typical of Ewing sarcoma in long bones is not seen commonly in the calvarium. The extra-dural soft tissue shows intense enhancement on contrast administration.

MR imaging provides better soft tissue delineation of these tumors. The extra dural soft tissue appears hypointense on T1 weighted images while the cystic and necrotic areas appear hyperintense on T2 weighted images. Good contrast enhancement is noted.
The differential diagnosis should include rhabdomyosarcoma, metastatic neuroblastoma and lymphomas.

Treatment is surgery followed by chemotherapy and radiation.

Suprasellar arachnoid cyst

Findings:

Figure 1, Figure 2 and Figure 3 show severe hydrocephalus involving the lateral and third ventricles.
Figure 4, Figure 5, Figure 6, show a suprasellar mass lesion which follows CSF signal on all sequences, including FLAIR.


Diagnosis: Suprasellar arachnoid cyst


Arachnoid cyst is the most common congenital lesion of the brain. It is typically an incidental imaging finding and is rarely symptomatic. However, in this case the size and location of the lesion in the suprasellar cistern resulted in severe obstructive hydrocephalus and precocious puberty. Both of these complications resolved following surgical drainage of the cyst.

Arachnoid cysts arise from a splitting of the arachnoid membrane with formation of a cyst wall consisting of fibrous connective tissue. There is no epithelial lining in the wall. Expansion occurs following trapping of cerebral spinal fluid through defects in the cyst wall. Arachnoid cysts occur most commonly in the middle cranial fossa and have a 4-to-1 male-to-female ratio. Even large cysts tend to be asymptomatic. Associated clinical features in symptomatic patients include headache, calvarial bulging, intracranial hypertension, craniomegaly, developmental delay, visual loss, precocious puberty, and seizures. Treatment of arachnoid cysts is not recommended by many unless there is a clear cause and effect relationship between the cyst and symptoms as shown in this case.

MRI is the preferred diagnostic modality for arachnoid cysts because of its ability to demonstrate the location, extent and relationship of the cyst to surrounding neurologic structures. Lesions typically have the signal intensity of CSF on all sequences, do not enhance and do not demonstrate restricted diffusion. The most important differential diagnostic consideration is between arachnoid and epidermoid cysts. Epidermoid cysts show restricted diffusion on diffusion-weighted images. In addition, unlike epidermoid cysts, arachnoid cysts show suppressed signal on fluid-attenuated inversion recovery (FLAIR) images.

Neuroblastoma metastases

Findings

Figure 1: Axial post gadolinium T1 weighted image showing solid enhancing parenchymal lesion in the right temporal lobe with dural and leptomeningeal disease.
Figure 2: Coronal post gadolinium image showing dural enhancement along the tentorium and leptomeningeal enhancement.
Figure 3: Axial susceptibility weighted imaging revealing the hemorrhagic nature of the lesion.


Diagnosis: Neuroblastoma metastases


Neuroblastoma metastatic to the central nervous system is extremely rare, and the reported incidence varies from 1% to 16% at recurrence. Paediatric tumors that metastasise to the brain, in order of frequency, include neuroblastoma, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma and Wilm tumor.

Risk factors for developing intracranial metastases include lumbar puncture at diagnosis, ages 2 to 3 years, bone marrow involvement, and MYCN gene amplification. Newer chemotherapeutic agents with better activity fail to penetrate the blood-brain barrier, thus facilitating a sanctuary for tumor cells within the central nervous system. As a result, the metastases evolve and become extensive before becoming clinically evident. Metastatic spread of tumor cells to central nervous system may occur either via hematogenous or cerebrospinal fluid routes and involve the neuroparenchyma, leptomeninges or dura.

Neuroparenchymal metastases from neuroblastoma have varied appearances. They may be cystic lesions with calcified mural nodules. The wall and mural nodules show intense enhancement with contrast. Metastases may also be solid and hemorrhagic and show homogeneous enhancement. Gradient or susceptibility weighted imaging would help in detecting hemorrhagic components. Leptomeningeal and dural metastatic involvement if present indicates poor prognosis.