What's 'GRE Susceptibility Vessel Sign' ?

(Above image showing the Susceptibility Vessel Sign : hypointense signal on SWI of right vertebral artery (V4 segment), more or less equivalent to hyperdense Vertebral Artery on CT).

Thrombi are mainly of three types based on their composition : platelet rich (white) thrombi, red thrombi containing rich fibrin network and RBCs and finally the mixed ones. White thrombi are formed mainly in atherosclerotic plaque ruptures, where as red thrombi are formed in low pressure systems like cardiac or venous systems.

The oxyhemoglobin which gets degraded into de-oxy hemoglobin, methemoglobin and hemosiderin, all have paramagnetic properties and produces susceptibility artifacts in GRE images. This concept is the main core of Susceptibility Vessel Sign.

Teaching Point : GRE SVS is associated with red thrombi and thereby favors a Cardio-Embolic Stroke in most cases. And it also signifies increased chance of subsequent spontaneous recanalization and also increased success rates with fibrinolytic therapy. 

 

Exceptions :

1.SVS –ve cardio-embolic thrombi : 

Can occur if MRI was taken before the degradation of Oxy-Hb to Deoxy-Hb (which usually occurs in few hours) OR due missing the section of small thrombus in GRE due to the interslice gap.

2.SVS +ve (Large Artery) Atherosclerotic thrombi :

due to the formation of white thrombus initially, can lead to stagnant or reduced flow velocity within the vessel, there by gradually causing increased fibrin and RBC content of thrombus.


References :
1. Significance of Susceptibility Vessel Sign on T2*-Weighted Gradient Echo Imaging for Identification of Stroke Subtypes. Kyung-Hee Cho, MD; Jong S. Kim, MD, PhD; Sun U. Kwon, MD, PhD; A-Hyun Cho, MD; Dong-Wha Kang, MD, PhD. Stroke, November 2005.

What's your Diagnosis? : Question 1

ANSWER HERE...

Calculus in Wharton's Duct in a post submandibular sialadenectomy patient !!

Female patient post sub-mandibular sialadenectomy for calculous sialadenitis. Now complaining of a sublingual hard swelling (at the site of opening of Wharton's Duct).

Above USG image is obtained from the right submandibular region, 

along the length of the Wharton's duct, with shows a terminal calculus, 

measuring ~8.5mm x 4.0mm, with duct measuring upto 3.9mm proximally.

Axial view from the neck, showing the calculus at the opening of right submandibular duct.

Chronic Pelvi-Ureteric Junction Obstruction (PUJO)

1 yr old child on follow-up for prenatally detected renal pelvic dilatation.

Marked renal pelvic dilatation is noted with gross hydronephrosis. The renal pelvis appeared 'ballooned' and the dilatation appears to be disproportionate to the degree of calyceal dilatation. 

The AP diameter of renal pelvis measures 39mm (3.9cm). The dilated pelvi-calyceal system is showing internal echogenic particles. There is no past history of UTI.

High resolution USG with the linear 12MHz probe showed better the
marked thinning of renal parenchyma, measuring ~2mm only.

View of the ballooned markedly dilated renal pelvis with the linear probe.

Pigmented Villo-Nodular Synovitis : 4th Toe !!

Aggressive ('Malignant') Hemangioma of Vertebrae

Vertebral hemangioma is a benign vascular tumor, usually affecting the vertebral body.

The typical benign (ones with fatty stroma) shows T1 and T2 hyperintense signal in MRI. In CT these show the pathognomonic 'Polka dot' appearance and 'corduroy' / 'jail house stripe' appearance in axial and coronal/sagittal sections.

The aggressive ('malignant') hemangiomas are T1 isointense to hypointense and T2 hyperintense with intense post-contrast enhancement. Pathologic fractures and epidural extension are common with aggressive hemangiomas. Cord compression can occur in the presence of epidural extension.

Aggressive Hemangioma features : 

Location common in D3 to D9 vertebrae, with extension into posterior elements, expansion, indistinct cortex, irregular honeycomb pattern and associated soft tissue mass.

Differential considerations in Aggressive Hemangioma include :

1. Metastases : Can be difficult, Correlative CT sections will be helpful.
2. Paget's Disease : Can also present with vertebral body expansion, but will not have soft tissue component.

T2 WI Sagittal image showing hyperintense lesion of L3 vertebra, with vertebral body expansion and soft tissue component. Marked spinal canal stenosis with cauda equina compression seen.

Unlike simple hemangioma with predominantly fatty stroma, which gets suppressed in STIR images, aggressive hemangiomas consists of more vascular tissue and usually remains hyperintense in STIR.

. 

T1 WI Sagittal and Axial Images, showing heterogeneous reduced signal intensity.

Intense enhancement in the post contrast images.

(1)Post contrast T1 FS Axial image. (2&3) correlative CT sections 

showing the irregular honeycomb appearance and indistinct cortex.

References : 

1. Diagnostic Imaging - Spine (Jeffrey.R.Ross), Ist Edition, 2004.

Intracranial Arachnoid Cyst : Galassi Type I

By definition an ARACHNOID CYST is an intra-arachnoid CSF-filled sac that does not communicate with the ventricular system. Best diagnostic clue is a sharply demarcated, round/ovoid extra-axial cyst that follows CSF density/signal and shows no diffusion restriction or enhancement.

As its an extra-axial lesion it does buckles the grey-white interface and may also remodel / cause scalloping / thin adjacent bone.

It comprises of ~1% of all intracanial masses. Majority (~60%) are located in the middle cranial fossa, anterior the the temporal lobe, with posterior displacement of MCA. Less common sites of arachnoid cysts include CP angle, Suprasellar region, convexity and quadrigeminal cistern.

The major differential diagnosis will be an epidermoid cyst, porencephalic cyst, neurenteric cyst and neuroglial cysts. DWI and T2 FLAIR sequences are the most helpful in arriving at a diagnosis.

Epidermoid cysts show diffusion restriction. These lesions are only partially suppressed in T2 FLAIR images and looks 'dirty'. These are plastic lesions, which instead of displacing vessels engulf them and insinuate into the sulcal spaces.

A porencephalic cyst will usually have history of previous trauma or infarct. And these are usually surrounded by gliotic areas, not displaced cortex.

Neuroglial cysts are usually intra-axial.

Neurenteric cysts are usually seen in posterior fossa and they often contain proteinaceous fluid.


The following images depict the typical imaging findings of a middle cranial fossa arachnoid cyst.

In the anterior temporal location, it may be associated with temporal lobe hypoplasia. Above image shows complete homogenous supression of the signal of the arachnoid cyst in T2 FLAIR images.

 Above image shows the lesion being isointense to CSF in T1 WI.

In DWI-ADC, contrast from an epidermoid cyst, the arachnoid cyst shows no diffusion restriction.

Galassi et al. had classified middle cranial fossa arachnoid cysts into 3 types long back in 1982, this classification is still being followed.

Type I cyst : Located in the Sylvian fissure, in the anterior temporal region, posterior to the sphenoid ridge, without any mass effect. These freely communicate with the subarachnoid space in Contrast CT cisternogram or in Phase Contrast MR evaluation.

Type II cyst : Located in the mid and proximal portions of Sylvian fissure, larger and rectangular in configuration. They communicate with subarachnoid space but slowly.

Type III cyst : Usually do not communicate with subarachnoid cyst, largest, lentiform in shape, will result in signficant mass effect and midline shift.


NOTE : A very large arachnoid cyst can show T2 slightly hypointense signal due to internal flow.

Vertebral Hemangiomas

.

T1 and T2 hyperintense lesions in D6, D7 and L1 vertebrae.

Diffusion negative Acute Infarct !! (False negative DWI)

Acute Embolic Infarcts

Vascular loops in Internal Acoustic Canal (IAC)

(Above CISS image showing type II Vacular loop (AICA) entering < 50% of the IAC lumen)