The Ascending Lumbar Communicant Vein

The ascending lumbar communicant vein is a communication between the left ascending lumbar vein and the left renal vein. Because of its retroperitoneal location, when dilated, it may be mistaken for a lymph node on non-contrast studies with thick collimation.

The image shows the left renal vein in yellow, the ascending lumbar communicant vein in red, and the lumbar vein in blue.

References

Yao Y, et al. Communicating Vein between the Left Renal Vein and Left Ascending Lumber Vein: Incidence and Significance on Abdominal CT. Radiation Medicine: 2003; 21(6) 252–257.

Benign Extra-Axial Fluid

Benign extra-axial fluid, previously known as idiopathic external hydrocephalus, is rapid head growth in neonates accompanied by increased fluid in the subarachnoid space.

It is detected typically between ages 3 and 8 months. The condition is self-limited with resolution of subarachnoid space enlargement by 2 years of age. Any developmental delay also resolves as the extra fluid resolves. The macrocephaly, however, usually persists. A family history of benign macrocephaly is also commonly seen.

Mild hydrocephalus is seen in 2/3 of patients. Grayscale ultrasound findings include sulcal dilatation with normal gyrus configuration. The cortical vein sign, initially described on MRI, can help differentiate subarachnoid fluid (seen in passive dilatation and benign extra-axial fluid) from subdural fluid (seen in trauma). Visualization of cortical veins within fluid collections localizes the collection to the subarachnoid space, making a subdural collection less likely.

Differential considerations include:

• Passive dilatation of the subarachnoid space due to brain atrophy
• Acquired extraventricular obstructive hydrocephalus
• Different stages of subdural hematoma, for example from nonaccidental trauma

References

• Chen CY, Chou TY, Zimmerman RA, Lee CC, Chen FH, Faro SH. Pericerebral fluid collection: differentiation of enlarged subarachnoid spaces from subdural collections with color Doppler US. Radiology. 1996 Nov;201(2):389-92.
• McCluney KW, Yeakley JW, Fenstermacher MJ, Baird SH, Bonmati CM. Subdural hygroma versus atrophy on MR brain scans: "the cortical vein sign". AJNR Am J Neuroradiol. 1992 Sep-Oct;13(5):1335-9.
• Seibert JJ, Avva R, Hronas TN, Mocharla R, Vanderzalm T, Cox K, Kinder D, Lidzy B, Knight KL. Use of power Doppler in pediatric neurosonography: a pictorial essay. Radiographics. 1998 Jul-Aug;18(4):879-90.

Monitoring for Fetal Anemia

An Rh-positive fetus in a sensitized mother should be monitored for fetal anemia. Serial amniocentesis for evaluation of bilirubin (the Delta OD₄₅₀) can be used to quantify fetal hemolysis.

Ultrasound can also be used by measuring the the peak systolic velocity (PSV) of the middle cerebral artery (MCA). Serial measures of MCA PSV are plotted as a function of gestational age and compared to control values.

Mari et al (2000) plotted the PSV of the MCA of fetuses with no anemia or mild anemia (open circles), moderate or severe anemia (triangles), and those with hydrops (solid circles). They found that fetuses with moderate or severe anemia had PSVs values greater than 1.50 times the median (dotted curve).

References

Mari G et al. Non-invasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. N Engl J Med 2000;342:9–14.

Cecal Volvulus and Bascule

A cecal bascule is a variant of cecal volvulus that is thought to result from anteromedial folding of the cecum in relation to the ascending colon without torsion. Cecal volvulus can occur due to clockwise or counterclockwise twisting of the cecum along its axis, in which case it ends up in the right lower quadrant. Cecal volvulus may also result from twisting and inversion of the ceccum, in which case it ends up in the left upper quadrant.

Chemical Shift Imaging of the Liver

Chemical shift imaging imaging is used for the detection of microscopic fat, whereas fat suppression techniques affect macroscopic fat.

Lesions with microscopic fat include:

• Focal or diffuse hepatic steatosis
• Hepatic adenoma
• Hepatic lipoma
• Well-differentiated hepatocellular carcinoma
• Hepatic angiomyolipoma
• Metastatic germ cell tumor
• Adrenal adenoma
• Renal cell carcinoma

Cystic Hygromas and Webbed Necks

A cystic hygroma ("moist tumor") is thought to form because of absent or delayed formation of lymphatico-venous connections, leading to lymphatic enlargement at the neck. The nuchal translucency is thought to represent a small cystic hygroma.

It is thought that delayed communication between the lymphatic and venous systems accounts for the resolution of cystic hygromas in some fetuses. In addition, some believe that the webbed neck and high hairline seen in patients with Turner syndrome are the sequella of resolved cystic hygromas.

References

Cystic Hygroma by Sabih D and Khan AN. eMedicine. Jul 17, 2008.

Ultrasound Dropout in in utero Detection of Septal Defects

Due to limited lateral resolution, an apical 4-chamber view of the heart may give the appearance of a ventricular or atrial septal defect if the septum is parallel to the ultrasound beam. A subcostal view should be obtained to determine if the VSD or ASD is real.

References

Chaoui R. Anomalies and Diseases of the Fetal Heart. In Eberhard Merz (Ed.), Ultrasound in obstetrics and gynecology. Georg Thieme Verlag. 2004.