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Neuroradiology Case of the Week
Case 445
October 2009
Balasubramanya Kolar, MD, Dhana Rekha Selvaraj,
and P-L Westesson, MD, PhD, DDS
Clinical
Presentation: A 47-year-old female presented with left-sided weakness in the face, upper extremity and lower extremity.
Imaging Findings: The initial non-contrast head CT showed hyperattenuating foci in right sylvian fissure and in interhemispheric fissure. No changes were detectable in the cerebral parenchyma. Subsequent diffusion-weighted MR images revealed infarcts in right MCA and ACA territories.
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Figure 1A: Axial non-contrast CT scan shows hyperattenuating dot in right sylvian fissure (arrow). |
Figure 1B: Hyperattenuating focus in right sylvian fissure, the MCA dot sign (arrow). |
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Figure 2A: Hyperattenuating focus in the interhemispheric fissure (arrow), the ACA dot sign.
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Figure 2B: Hyperattenuating dot in interhemispheric fissure towards the right side (arrow). |
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| Figures 3A-D: Diffusion-weighted MR images show infarcts in the right MCA and ACA territories. |
Diagnosis: Dot sign as an early indicator of MCA and ACA infarction
Discussion: The imaging protocol for stroke begins with non-contrast head CT scan to rule out hemorrhage. The parenchymal changes in CT are delayed as compared to diffusion-weighted MR imaging. The role of CT in this setting has gained importance with the description of signs for demonstrating the clot with the occluded vessels, suggesting infarction in that arterial territory indirectly. These include the hyperdense vessel sign and the more recent, dot sign [1].
Hyperdense vessel sign is described for the thromboembolus within the M1 segment of MCA [2]. This has been described in 17 to 50% of patients with MCA stroke [3]. However the specificity is high, approaching 100% [4] and the sign has also been associated with poor clinical outcomes and extensive territories of infarction [3].
The MCA dot sign is a variant of hyperdense vessel sign. The dot sign is described as a punctate focus of hyperattenuation seen in the sylvian fissure as compared to the other side [4]. This occurs due to a thromboembolus within a segmental branch of middle cerebral artery. The sign has been correlated histopathologically with the accumulation of erythrocytes, fibrin and cellular debris [6]. The dot is due to perpendicular course of the branches from M2 and M3 segments of MCA in contrast to the M1 segment which courses parallel to the imaging plane in axial CT sections. This sign has been validated against subsequent cerebral angiograms in 54 acute stroke patients within 8 hours of symptom onset, and was found to have sensitivity of 38%, specificity of 100%, positive predictive value of 100% and negative predictive value of 68% [7].
Though the dot sign has been classically used for MCA occlusion, it can be extended to describe the clot within ACA also. The A2 segment ascends in the interhemispheric fissure and runs perpendicular to the imaging sections in axial cuts, again giving rise to a dot if occluded with a thrombus.
The hyperdense vessel sign and the dot sign can be used to predict the prognosis. The latter if found in isolation suggests more distal vessel occlusion, smaller territory involvement and thereby a better prognosis, as compared to the former [3].
Conclusion: The dot sign can occur with occlusion of segmental MCA branches as well as A2 segment of ACA. The dot sign is highly specific, serves as an indicator of distal branch occlusion, and can have important therapeutic and prognostic implications.
References:
- Shetty SK. The MCA dot sign. Radiology. 2006 Oct;241(1):315-8. PMID: 16990684 [PubMed]
- Pressman BD, Tourje EJ, Thompson JR. An early CT sign of ischemic infarction: increased density in a cerebral artery. AJR Am J Roentgenol 1987;149(3):583–586. PMID: 3497548 [PubMed]
- Somford DM, Nederkoorn PJ, Rutgers DR, Kappelle LJ, Mali WP, van der Grond J. Proximal and distal hyperattenuating middle cerebral artery signs at CT: different prognostic implications. Radiology. 2002 Jun;223(3):667-71. PMID: 12034933 [PubMed]
- Leys D, Pruvo JP, Godefroy O, Rondepierre P, Leclerc X. Prevalence and significance of hyperdense middle cerebral artery in acute stroke. Stroke. 1992 Mar;23(3):317-24. PMID: 1542889 [PubMed]
- Barber PA, Demchuk AM, Hudon ME, Pexman JH, Hill MD, Buchan AM. Hyperdense sylvian fissure MCA "dot" sign: a CT marker of acute ischemia. Stroke 2001Jan;32(1):84–88. PMID: 11136919 [PubMed]
- Rutgers DR, van der Grond J, Jansen GH, Somford DM, Mali WP. Radiologic-pathologic correlation of the hyperdense middle cerebral artery sign: a case report. Acta Radiol 2001Sep;42(5):467–469. PMID: 11552883 [PubMed]
- Leary MC, Kidwell CS, Villablanca JP, et al. Validation of computed tomographic middle cerebral artery "dot" sign: an angiographic correlation study. Stroke 2003 Nov;34(11):2636–2640. PMID: 14593125 [PubMed]
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