Popliteal artery aneurysms are the most common peripheral arterial aneurysm. They are usually true aneurysms resulting from atherosclerosis or arteriomegaly. False aneurysms may arise from knee trauma, surgery or infection.

True aneurysms of the popliteal artery are commonly bilateral (50 to 70%) and frequently associated with abdominal aortic aneurysms (30 to 50% have a AAA). There is a strong male preponderance with a male to female ratio of 15:1. These aneurysms rarely rupture; the main complications are thrombosis and distal embolism. For this reason asymptomatic aneurysms greater than 2 cm diameter are considered for elective treatment with endovascular insertion of a covered stent, or with open surgical repair.

Reference: Radiopaedia.org

Duodenal diverticula are usually acquired pseudodiverticula and most arise along the concave border of the second or third parts of the duodenum. 75% arise within 2 cm of the ampulla of Vater and it is not uncommon for the ampulla to empty into the diverticulum.

Insertion of the ampulla into a duodenal diverticulum is clinically important for several reasons. Firstly, it may cause difficulty with retrograde cannulation of ampulla during ERCP, or antegrade cannulation into the main duodenal lumen during percutaneous biliary intervention. Secondly, it is important to recognise if duodenal surgery is contemplated. Thirdly, stasis of duodenal contents within the diverticulum may cause partial obstruction of ampullary drainage, which is believed to predispose to biliary calculi, cholangitis and pancreatitis.

References:
1. Medcyclopaedia.com
2. Schulze K. Review of duodenal diverticula, Radiology, 1992;183:554

May-Thurner syndrome is deep venous thrombosis resulting from chronic compression of the left common iliac vein (CIV) against the lumbar vertebrae by the overlying right common iliac artery (CIA). Although both left and right CIVs lie deep to the right common iliac artery, the left CIV has a more transverse course and is predisposed to compression whereas the right CIV ascends more vertically and is therefore not similarly predisposed. First line treatment is with thrombolysis and stenting, which removes the clot and relieves the compression to prevent recurrence.

Reference: Radiopaedia.org

This coronal T1W post-gadolinium MR image shows a cystic cerebellar tumour with an enhancing mural nodule. The patient is a 20-year-old male. Pathologically-proven haemangioblastoma.

Axial PD image shows prominent flow voids associated with the solid portion of the tumour, a frequent finding in haemangioblastoma.

Also see these previous cases: case one; and case two.

Constellation of neurological signs due to a lesion at the facial colliculus, involving

* Abducens nerve (CN VI) nucleus
* Facial nerve (CN VII) fibres at the genu
* Medial longitudinal fasciculus

and resulting in peripheral facial palsy and conjugate gaze palsy.

The facial palsy is due to interruption of the ipsilateral facial nerve fibres at the genu as they arch behind the abducens nerve (CN VI) nucleus (thus forming the colliculus).

The conjugate gaze palsy is due to involvement of innervation not only to the ipsilateral abducens nerve to lateral rectus, but also to the interneurons projecting into the medial longitudinal fasciculus which contribute to innervation of the contralateral medial rectus (thus coordinating conjugate gaze). This is not however always the case (this case), as you can see the dysconjugate gaze on the T2 FSE)
Aetiology

Causes of facial colliculs syndrome vary by age:

* Young:
o tumour
o demyelination (e.g MS)
o viral inection (e.g rhomboencephalitis)
* Older:
o vascular (e.g stroke - this case)

References:

D.A. Jacobsa and S.L. Galettaa “Neuro-Ophthalmology for Neuroradiologists” American Journal of Neuroradiology 28:3-8, January 2007

For more images of the case and many more, please visit Radiopaedia.org here.

* progressive myopia (aka mega myope) most common cause.
* glaucoma
* scleritis
* necrotizing infection
* surgery / trauma
* radiotherapy

Anterior staphyloma

Seen seconday to inflammation or infection of the sclero-corneal lining of the eye.

References:
1. M Mafee, GE Valvassori, M Becker “Imaging of the Head and Neck” Thieme 2005 2nd Ed.
2. D Osborne, GN Foulks “Computed Tomographic Analysis of Deformity and Dimensional Changes in the Eyeball” Radiographics 1985; 153:699-674

For more on staphylomas please visit Radiopaedia.org here.

Endoleak is a common complication of EVAR found in up to 40% of patients. It is seen on CTA, MRA and DSA as contrast opacification of the aneurysm sac outside the graft. Flow in the sac may also be detected on ultrasound. When an endoleak occurs, flow within the aneurysm sac is at systemic or near-systemic pressure. If untreated, the aneurysm may expand and is at risk of rupture. Aneurysm expansion following EVAR always warrants investigation for endoleak.

There are several causes of endoleak which are classified into 5 types as follows:
Type I – leak at graft attachment attachment site.
Type II – aneurysm sac filling via branch vessel (most common).
Type III – leak through defect in graft.
Type IV – leak through graft fabric as a result of graft porosity.
Type V – continued expansion of aneurysm sac without demonstrable leak on imaging (endotension).

Types II and IV usually resolve spontaneously. Type I and III do not, and require immediate treatment. Endoleak may become evident intra-operatively, or months or years later. Therefore life-long imaging surveillance is necessary, usually performed with CTA.

References:
1. Rosen RJ & Green RM. Endoleak Management following Endovascular Aneurysm Repair, Journal of Vascular and Interventional Radiology, 2008;19:S37-S43
2. Kaufman J & Lee M, Vascular & Interventional Radiology The Requisites, Mosby 2004

A DNET is a benign intracortical mass, typically multinodular in appearance, with a ‘bubbly appearance’. It coexists with an area of cortical dysplasia, and is characteristically the cause of intractable partial seizures. It demonstrates essentially no growth over time, although very gradual increase in size has been described.

Location
- hippocampal formation and amygdala (most common) - (see case 1)
- caudate nucleus
- septum pellucidum

DDx
Medial temporal lobe

- Tumours (in order of decreasing frequency)
- Ganglioglioma
- low grade astrocytoma
- Pleomorphic xanthoastrocytoma

- Cysts
- neuroepithelial cyst
- choriod fissure cyst
- Other
- herpes simplex encephalitis - usually some bilateral changes, and different presentation.
- limbic encephalitis- usually some bilateral changes, and different presentation.
- mesial temporal sclerosis
- cortical dysplasia

References:
- Neuroradiology: The Requisites
- Brain: Diagnostic imaging by Osborn

For more images of the same case please visit here.
For more on DNET please visit Radiopaedia.org here.