Post-traumatic Syrinx

A syrinx is an intradural, intramedullary, well-defined collection of fluid that follows CSF signal intensity on all MRI sequences. In some patients, the signal is brighter than CSF on T1WI and darker that CSF on T2WI, possibly due to higher protein content secondary to cord edema. 

The etiology of a syrinx can be developmental such as in the Chiari/Dandy Walker malformations or secondary to trauma, tumors, inflammation and ischemia. In cases of an unexplained syrinx, one should suspect a tumor and imaging with gadolinium may be obtained to search for a source.

The above images are from a patient who suffered a retropulsed T6 fracture. Caudal expansion of the central canal with a CSF containing structure is most consistent with a post-traumatic syrinx.

REFERENCES

Brant WE, Helms CA. Fundamentals of diagnostic radiology. Lippincott Williams & Wilkins. (2007).
Potter K and Saifuddin A. MRI of chronic spinal cord injury. Brit J Radiol 2003;76:347-352.

The Reversal Sign

The reversal sign refers to the inversion of the normal attenuation relationship between gray and white matter on NECT. The result is a higher attenuation of the thalami, brainstem, and cerebellum relative to the surrounding gray matter. The finding indicates diffuse cerebral edema secondary to anoxic injury and is associated with a poor prognosis.

Several theories regarding the pathogenesis of the reversal sign exist:
1. Transtentorial herniation relieves pressure on the central structures which improves tissue perfusion in the posterior fossa.
2. Hypoxia induces neovascularity in regions of normally high metabolism and capillary density.
3. Hypoxia causes petechial hemorrhages in the regions of relatively increased attenuation.
4. Increased intracranial pressure causes venous outflow obstruction and distention of deep medullary veins.
5. Elevated serum (brain) glucose levels during anoxia causes preferential damage to the cortex with relative preservation of the thalami and brainstem.

REFERENCES

Han BK, Towbin RB, De Courten-Meyers G, et al. Reversal sign on CT: effect on anoxic/ischemic cerebral injury in children. AJNR Am J Neuroradiol 1989;10:1191-1198.
Kavanagh EC. The reversal sign. Radiology 2007;245:914-915.

Cavernous Transformation of the Portal Vein

Cavernous transformation of the portal vein (CTPV) is the development of venous channels around a thrombosed portal vein to serve as portoportal collaterals. There are two accepted theories explaining the pathogenesis of CTPV: 1. congenital agenesis of the portal vein leads to periportal collateralization and 2. that it is a portal vein hemangioma.

The main causes of portal vein thrombosis in adults are hepatocellular carcinoma, pancreatitis, cirrhosis, liver transplantation, and splenectomy. CTPV may occur in as little as 6-20 days after the insult to the portal vein.

CECT will characteristically show a mass of veins with a beaded appearance at the porta hepatis. Intrahepatic extension of the cavernous transformation can occur. Hepatic arterial phase imaging will demonstrate heterogeneous, patchy areas of high attenuation along the liver periphery (collateral channels better supply the central regions of the liver causing increased peripheral arterial inflow).

Doppler ultrasound shows hepatopetal flow in the cavernoma lacking the respiratory undulation of a normal portal vein.

The images above are from a patient with a patent main portal vein but thrombosis of the left and segments of the right portal veins, with CTPV formation.

References

De Gaetano AM, Lafortune M, Patriquin H, et al. Cavernous transformation of the portal vein: patterns of intrahepatic and splanchnic collateral circulation detected with Doppler sonography. AJR Am J Roentgenol 1995; 165:1151–1155. 

Gallego C, Velasco M, Marcuello P, et al. Congenital and acquired anomalies of the portal venous system. Radiographics. 2002 Jan-Feb;22:141-159.

Posterior Dislocation of the Sternoclavicular Joint

Sternoclavicular joint dislocations are rare, with anterior types being most common. Posterior (or retrosternal) dislocations are usually secondary to a direct blow to the posterolateral shoulder and are associated with higher morbidity and fatal complications. They can effect structures in the thoracic outlet and anterior mediastinum causing damage to the trachea, great vessels and nerves (brachial plexus, recurrent laryngeal). Posterior dislocations are typically reduced in the operating room.

References

McCulloch P, Henlet BM, Linnau KF. Radiographic clues for high energy trauma: three cases of sternoclavicular dislocation. AJR Am J Roentgenol. 2001 June;176:1534.
Restrepo CS, Martinez S, Lemos DF, et al. Imaging appearances of the sternum and sternoclavicular joints. Radiographics. 2009 May-June;29:839-859.

New Beginnings

Please join me in welcoming Dr. Saba Gilani as the new editor of Roentgen Ray Reader. Dr. Gilani brings with her a collection of interesting cases of relevance to day-to-day practice, and, more importantly, will inject some much needed fresh energy into the blog.

End of the Road

Dear readers,

The recent time off from the blog to work on a chapter has had an unexpected inertia, and it's been hard to get back into the daily routine of coming up with interesting things to write about. Upcoming clinical and academic responsibilities will make it even harder to squeeze the 1-2 hours needed for each post and provide the time and attention that a wife and cat require.

If you'd like to continue the work, let me know and the blog can be yours. I found the effort to be very worthwhile during residency and fellowship, and highly recommended it not only as a self-education tool, but as a great resource/peripheral brain.

Thanks for your support and kind comments over the past 3 years.

-Behrang

Malignant Mixed Müllerian Tumor

Malignant mixed müllerian tumors (MMMTs), make up about half of all uterine sarcomas, but can originate anywhere along the lower female genital tract. Also known as carcinosarcomas, MMMTs contain both epithelial and stromal elements, unlike other uterine sarcomas, which contain only stromal elements. Advanced age, excess estrogen exposure, nulliparity, prior pelvic irradiation, and tamoxifen have been implicated as risk factors.

The uterus is most commonly involved organ. Ultrasound findings include expansion of the endometrial cavity with an intrauterine mass. The mass is usually hyperechoic to normal myometrium; however, homogeneous echogenic thickening of the endometrium can be the only finding.

CT will also depict expansion of the endometrial cavity (see images above) with an internal mass. The mass can be ill-defined or well-defined, but is usually heterogeneous and lower in attenuation compared to the normal myometrium. Areas of higher attenuation and calcifications can also be seen.

On MRI, MMMTs are heterogeneously hyperintense on T2-weighted images and slightly hypointense on T1-weighted images. Scattered areas T1-hyperintensity may be present, and there is heterogeneous and avid enhancement.

It is important to assess for myometrial involvement, metastatic pelvic and retroperitoneal lymphadenopathy, carcinomatosis, and adnexal involvement.

References

Teo SY, Babagbemi KT, Peters HE, Mortele KJ. Primary malignant mixed mullerian tumor of the uterus: findings on sonography, CT, and gadolinium-enhanced MRI. AJR Am J Roentgenol. 2008 Jul;191(1):278-83.