Address correspondence to: Bryann Bromley MD, Diagnostic Ultrasound Associates, 333 Longwood Avenue, Boston, MA 02115. From the Departments of Obstetrics & Gynecology and Radiology, Brigham & Women"s Hospital, and Radiology and Neurosurgery at Children"s Hospital, Harvard Medical School, Boston, MA.

Introduction

Prenatal sonography is commonly used to detect central nervous system abnormalities. The most frequent intracranial anomalies are echolucent and represent fluid collections, such as ventricular enlargement, intracranial cysts or vascular malformations. Echogenic masses of the fetal brain are far less common and often present diagnostic dilemmas. We describe the sonographic appearance of 8 fetuses with echogenic intracranial masses diagnosed antenatally. The differential diagnosis includes intracranial tumors, lipomas of the corpus callosum, intracranial hemorrhages, and calcifications. The outcome for these fetuses is variable, with 4 neonatal deaths, 2 others developmentally delayed, and 2 seemingly normal at 5-9 months of ages.

Materials and methods

Images of eight fetuses with echogenic intracranial masses were retrospectively reviewed in terms of gestational age at presentation and sonographic findings. Increased echogenicity was defined as echogenicity equal to or greater than that of the choroid plexus. Postnatal follow-up was obtained from pediatric hospital charts, postnatal radiologic studies, and autopsy records. All patients were scanned with an Acuson 128 variable focus sector 3.5 MHz trans- ducer or a transvaginal 5 MHz transducer.

Results

The clinical and sonographic findings of these 8 fetuses are shown in Table 1.

Table 1: Case presentations.

Intracranial teratoma

Two fetuses (cases 1 and 2) (fig. 1-2) presented at 26 and 29 weeks with severe macrocephaly and complete replacement of the intracranial contents by an inhomogeneous echogenic mass. The mass extended into the oropharynx in both fetuses. Postnatal autopsy on both infants revealed massive intracranial teratomas causing severe macrocephaly and distorting intracranial anatomy. In case 1, the tumor invaded through the palate and protruded from the mouth; the external portion of the tumor measured 100*70*40mm. In case 2, the tumor protruded through the mouth as well as the left orbit.

Figure 1: Case 1: Transverse view of the fetal head at 26 weeks showing complete replacement of the brain by a complex echogenic mass, expanding the cranium.

Figure 2: Case 2: Longitudinal view of the fetal facial profile at 29 weeks, showing extension of the tumor through the mouth (arrows).

Primitive neuroectodermal tumor

In a third fetus (case 3) (fig. 3), presenting at 34 weeks" gestation, the posterior fossa was completely replaced by a large echogenic mass, obscuring recognizable landmarks. The fetus was delivered at 34 weeks gestation due to poor antenatal testing but died shortly after birth. Post-mortem examination of the brain showed a primitive neuroectodermal tumor arising in the pons and cerebellum, as well as an intraventricular hemorrhage in the fourth ventricle and bilateral germinal matrix hemorrhages. The infant had severe hydrocephalus and macrocrania.

Figure 3: Case 3: Coronal view of the posterior fossa showing an echogenic mass replacing the cerebellum, and severe hydrocephalus.

Lipoma of the corpus callosum

Two fetuses (cases 4, 5) (fig. 4-5) presented late in the third trimester with echogenic masses in the midline of the fetal brain above the third ventricle and extending into the lateral ventricles. Both infants were born at term. Postnatal MRI and CT showed lipomas with partial agenesis of the corpus callosum and ventriculomegaly. One infant underwent vertriculoperitoneal shunting for hydrocephalus. This infant is developmentally delayed at 6 months of age. The other infant has not required shunting and is developing appropriately at 5 months of age.

Figure 4: Case 4: Transverse view of the fetal head at 33 weeks, showing an echogenic mass above the third ventricle in the location of the corpus callosum (arrow).

Figure 5: Case 5: Coronal view of the fetal brain at term, showing an echogenic mass in the location of the corpus callosum, with extension into the choroid plexus bilaterally (arrows).

Intracranial hemorrhage

Massive intracranial hemorrhages occurred in two fetuses (cases 6, 7): one at 18 weeks and the second at 31 weeks. Each of these fetuses was one of a twin set. Case 6 was a monochorionic-diamniotic twin from a pregnancy complicated by twin-to-twin transfusion syndrome managed with serial amniocenteses. At 31 weeks" gestation, the smaller twin had hydrops and an echogenic mass partially replacing one of the cerebral hemispheres, prompting delivery. The affected twin underwent a postnatal cranial sonogram showing a large hemorrhagic infarct of the right temporal and parietal lobes. This infant appears to be developing appropriately as of 9 months of age. In Case 7, a dichorionic-diamniotic twin presented at 17 weeks gestation with a large echogenic mass occupying one side of the fetal brain, causing shift of midline structures. The affected twin died in utero two weeks later, followed closely thereafter by the demise of the normal appearing co-twin.

Figure 6: Case 6: Coronal view of the fetal brain at 31 weeks, showing a large echogenic mass involving the right parietal area.

Figure 7: Case 7: Transverse view through the fetal head at 18 weeks, showing an echogenic mass in one side of the fetal brain, with a shift of the midline.

Lissencephaly

In the last case (case 8), multiple punctate intracranial calcifications were seen at 22 weeks" gestation, with a rim of calcification in the deep white matter (fig. 8). This fetus subsequently developed microcephaly in the third trimester and was found, on postnatal cranial computed tomography, to have severe intracranial calcifications, with an unusual gyral pattern, suggesting lissencephaly. The TORCH titers were not suggestive of acute infection. The infant is severely developmentally delayed at 9 months of age.

Figure 8: Case 8: Two transvaginal views of the fetal brain at 22 weeks, showing abundant intracranial calcifications (arrows) in the deep white matter.

Discussion

The brain is easily imaged in the second and third trimesters because of differences in echogenicity between brain parenchyma and specular reflections from the coverings of the brain. Normally echogenic structures in the fetal brain include the choroid plexus, leptomeninges, ventricular walls, deep penetrating veins, and the cerebellar vermis^7,9. Aside from these areas, all of which conform to known anatomic landmarks in the brain, an intracranial echogenic mass is likely to be associated with significant pathology.

Intracranial teratomas tend to be echogenic complex masses with cystic and solid components. They may grow rapidly, distorting normal intracranial structures, and may extend extracranially as well^3,10,14. Other common intracranial tumors of the neonate include primitive neuroectodermal tumors, astrocytomas, malignant germ cell tumors and choroid plexus neoplasms^1,15. It may be difficult to differentiate an intracranial hemorrhage from tumor; in addition, hemorrhage may occur within a tumor.

Fetal intracranial hemorrhages are rare and may result in hydrocephalus^4,6,8,11,12.

Lipoma of the corpus callosum is a rare congenital anomaly presenting as a highly echogenic mass in a characteristic midline location in the interhemispheric fissure. The lipoma may extend into the lateral ventricles and involve the choroid plexus. In approximately 50% of cases, there is partial or complete agenesis of the corpus callosum^2,13. Prognosis for the fetus with corpus callosum lipoma is variable. Symptoms may include seizures, headache, mental retardation, hemiparesis, vomiting and vertigo in 50% of patients¹³. Surgical resection is not carried out for these stable lesions which do not produce and enlarging mass; therefore, management is directed towards the treatment of symptoms².

Intracranial calcifications tend to be punctate and scattered, often in a periventricular location, without disturbing midline structures. These calcifications are often associated with infection inutero and may result in micro- or macrocephaly, as well as sensory neural loss⁵.

The cases described in this report show that diagnostic possibilities for an echogenic mass in the fetal brain include lesions composed of blood, fat or calcium. Echogenic masses in the brain, particularly those causing shift of midline structures, usually carry a poor prognosis.

References

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