Focal Nervous System Lesions

TUMORS

Central nervous system tumors in the neonatal period may occur in the brain and spine. Magnetic resonance imaging is the study of choice for neonates with suspected brain or spinal tumors. Brain tumors may be supratentorial or infratentorial. Supratentorial tumors are more frequent than infratentorial tumors.
Supratentorial tumors may produce obstetrical complications due to severe macrocephaly, or may present in the neonatal period as hydrocephalus, focal neurological findings, or systemic signs of massive bleeding such as anemia or hypotension. Teratomas, astrocytomas, choroid plexus papilloma, and primitive neuroectodermal tumors are the most frequent supratentorial brain tumors in neonates.
Teratomas constitute about one-third of all neonatal tumors (Figure 257.1).

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Figure 257.1.— MRI of the brain demonstrating a large teratoma. The tumor involves the left optic nerve [A] and extends beyond the skull [B and C]. Calcifications are present [B and C].

Astrocytomas also occur frequently. Astrocytic tumors may occur in neonates with tuberous sclerosis. Choroid plexus papillomas are usually in the lateral ventricles and produce hydrocephalus. Choroid plexus papillomas have been described in neonates with Aicardi syndrome and melanocytic nevus. Choroid plexus papillomas have the best prognosis of all neonatal brain tumors.
Primitive neuroectodermal tumors (Figure 257.2) are highly aggressive tumors that metastasize widely within the cerebrospinal fluid. Neonates with rhabdoid tumors of the liver or Wilms tumor have a higher incidence of primitive neuroectodermal tumors.

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Figure 257.2.— Primary neuroectodermal tumor. [A] Contrast enhanced lesion obstructing the left foramina of Monro. [B] T1- transverse view demonstrates a hypointense mass obstructing the left foramina of Monro.

Optic gliomas may occur in neonates with neurofibromatosis type I.

Infratentorial tumors may occur in neonates. Infratentorial tumors are less frequent than supratentorial tumors. They usually presents with signs of brainstem dysfunction, hydrocephalus or both. An infrequent presentation of infratentorial tumors in neonates consists of epileptic seizures characterizes by facial twitching and apnea. Infratentorial tumor may be diagnosed by ultrasound through the mastoid fontanelle (Figure 257.3), but MRI of the brain is the study of choice.

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Figure 257.3.— [A] Anterior fontanelle ultrasound demonstrating large lateral ventricles and small nodule protruding into the right ventricle. [B] Mastoid fontanelle ultrasound demonstrating a hyperechogenic mass in the posterior fossa. This patient had tuberous sclerosis.

MRI of the brain with and without contrast (Figure 257.4) alouds better definition of the tumor.

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Figure 257.4.— [A] Sagittal MRI of the brain demonstrating a large posterior fossa tumor (contrast) and dilatation of the third ventricle. [B] Hematoxylin-eosin stain of tumor tissue demonstrating a solid proliferation of large balloon cells with abundant glassy to finely granular or foamy eosinophilic cytoplasm with frequent eccentric uniformly regular nuclei with bland chromatin and a distinct nucleoli. The histology was consistent with a subependymal giant cell astrocytomas.

Most frequent infratentorial tumors are primitive neuroectodermal in nature and astrocytomas. Hamartomas of the cerebellum (Figure 257.3) are rare but they should be consider in patients with apneic seizures and facial twitching. More about brain tumors... 46, 288

Spinal cord tumors usually present as lower extremity diplegia since they tend to occur below the cervical spine. The most frequent spinal cord tumor is neuroblastoma (Figure 257.5). Astrocytomas and teratomas may also occur.

Figure 257.5.— MRI of the spine demonstrating a neuroblastoma compressing the spine.

ABSCESS

Central nervous system absceseses in the neonatal period may occur in the brain and spine. Two-thirds of brain abscesses occur in association with meningitis. The most common organisms are Citrobacter diversus, Proteus, and Pseudomonas. Every neonate with gram-negative bacterial meningitis should be evaluated for the possibility of an abscess. Multiple absceseses are usually present. Seizures, signs of sepsis, and increasing head circumference are the most common clinical manifestations. Magnetic resonance imaging of the brain is the study of choice to diagnose brain abcess (Figure 257.6). Well-formed abscesses should be drained. In most cases surgical aspiration should be attempted. If surgical aspiration fails to collapse the abscess, open surgical drainage is recommended. Antibiotic therapy should be adjusted based on the cerebrospinal fluid findings or preferably on the findings in the material collected from the abscess.

Figure 257.6.— MRI of the brain demonstrating a brain abscess with surrounding edema producing ventricular compression. In addition, there are multiple isolated areas of increased signal.

PORENCEPHALY

Porencephaly may present as hemiparesis, seizures, or both. Porencephaly refers to an intraparenchymal cavity that is isointense to the cerebrospinal fluid in all MRI sequences. It can be distinguished from schizencephaly because the cavity is not lined by a cortex-like band. The cause of porencephaly is local ischemia after the 26 weeks gestational age. The evaluation of a neonate with porencephaly should be similar to the evaluation of a neonate with an ischemic arterial infarct.

SCHIZENCEPHALY

Schizencephaly is usually clinically silent in the neonatal period, but it may present as hemiparesis, seizures, or both. Schizencephaly can be diagnosed by CT or MRI of the brain (Figure 257.7 [A] [B]). Schizencephaly refers to a cavity lined by a cortex-like band that is isointense to the cerebrospinal fluid in all MRI sequences (Figure 257.7 [B]). The cavity may be so narrow that the cortex-like bands appear adjacent to each other (closed lips) (Figure 257.4 [A]) or so wide that the cortex-like bands are very far from each other (open lips) (Figure 257.7 [B]). Schizencephaly may be sporadic or familial.

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Figure 257.7.— [A] CT of the brain demonstrating closed-lip schizoencephaly. [B] MRI of the brain demonstrating open-lip schizoencephaly.

Schizencephaly may be associated with other central nervous system malformations. Neonates with schizencephaly should have a neuro-ophthalmological evaluation. Schizencephaly may be associated with de Morsier syndrome (Figure 257.8).

Figure 257.8.— MRI of the brain in a patient with the association of de Morsier syndrome (bilateral optic nerve atrophy) and schizencephaly.

de Morsier's syndrome consists of atrophic optic nerves (Figure 257.9) and endocrine problems. More about... 46

Figure 257.9.— [A] Atrophic optic nerve: lack of sharp borders and increased vessel-size to disc-size relation. [B] Normal optic nerve: sharp borders and normal vessel-size to disc-size relation.