Juvenile angiofibroma

The most common benign nasopharyngeal tumour. It is probably hamartomatous in origin. Although benign it can grow to an enormous size and invade local structures.

It is seen virtually exclusively in males, usually in teenagers.

It is a highly vascular tumour which can present with severe epistaxis. Biopsy is extremely hazardous due to the risk of haemorrhage. Part of the radiological work up should assess the extent of the lesion and its vascularity. Some require embolisation prior to surgery to reduce the blood supply.

MR is better at showing the soft tissue extent of the tumour. Subtle bone destruction requires CT.

Characteristically the tumour is of low to intermediate signal intensity on both T1 and T2 weighted sequences. Discrete punctate areas of hypointensity are seen due to flow void channels in highly vascular stroma.

Bronchopulmonary sequestration

• Is more common in males.
• Is more common on the left. Usually the posterior basal segment of the left lung lower lobe.
• May communicate with the oesophagus. It arises as an accessory tracheobronchial foregut bud, hence its systemic arterial supply.
• Intralobar is more common than extralobar sequestration. Intralobar is about 3 times more common and usually presents in adulthood. It is enclosed by the visceral pleura of the affected pulmonary lobe.
• Systemic feeding vessels originate from the descending thoracic aorta. Vascular drainage into the left atrium occurs through the normal pulmonary veins resulting in a left-to-left shunt. Associated congenital abnormalities are rare.
• Extralobar sequestration has its own pleural sheath which prevents collateral air drift and usually presents in neonates. 90% are contiguous with the left hemidiaphragm in the thorax.
• Systemic feeding vessels commonly originate from the thoracic or abdominal aorta (80%), or from the splenic, gastric, subclavian or intercostal arteries. Vessels drain into the systemic circulation through the IVC, azygos or hemiazygos veins. Associated congenital abnormalities are frequent.

Osteoid osteoma

Osteoid osteoma accounts for approximately 10% of benign primary bone tumours and is almost always accompanied by pain. The pain increases at night and is usually relieved by salicylates.

Epiphyseal involvement is extremely rare. It is usually diaphyseal in origin although extension to the metaphysis does occur.

Common sites include the femur and tibia which account for 60% of the lesion sites. 20% of lesions arise in the hands and feet. It occasionally occurs in the posterior elements of the spine usually in the lumbar region, although involvement of the vertebral body can occur. In the spine the tumour is usually associated with a scoliosis and is located at the concave surface.

Typically a rounded central lucency is present measuring less than 1 cm. This nidus contains variable amounts of punctate calcification. There is eccentric bone expansion and surrounding dense sclerosis and periosteal reaction.

Osteoid osteoma typically exhibits moderate tracer uptake in the zones of bony sclerosis with marked uptake in the region of the nidus. This pattern of uptake is called the "double density" sign. On CT the nidus enhances after administration of IV contrast.

Ovarian torsion

• Ovarian torsion usually presents in the first three decades of life and is predisposed in patients with co-existing ovarian pathology such as follicular cyst. 
• There may be history of similar episodes indicating intermittent torsion and spontaneous detorsion.
• Torsion causes venous outflow obstruction and engorgement of the ovary. Eventually arterial supply is compromised and necrosis ensues.
• Diagnosis is suggested by unilateral enlargement of a round or oval-shaped ovary containing multiple enlarged peripheral cysts (caused by transudation of fluid into follicles). Free fluid is present in the majority of cases. Peripheral blood flow may be present but may be absent with infarction.
• Ovarian hyperstimulation can present with abdominal pain and may show an enlarged multicystic ovary associated with ascites. However, the condition usually arises from ovarian hormone stimulation in the setting of infertility.
• Polycystic ovary syndrome typically presents with menstrual disturbance, obesity and hyperandrogenism.

Endometrial polyp

• Endometrial polyps are common benign tumours of the endometrial cavity.
• They are most common after the age of 40 years and are rare before menarche.
• Typical ultrasound appearance is of a hyperechoic endometrial mass which may or may not contain cystic spaces. A feeding vessel is often demonstrated from its base on power Doppler.
• NB: Submucosal fibroids are generally of reduced echogenicity (hypoechoic).
• On MRI, a mass which contains a central fibrous core that enhances post-contrast and also contains well-demarcated T2-hyperintense cysts suggests endometrial polyp.
• An intact junctional zone and smooth tumour-myometrial interface also favour a polyp.

Retrospective ECG-gated spiral scanning

•  For "retrospectively ECG-gated spiral scanning" a continuous spiral scan is acquired with the ECG-signal recorded simultaneously. 
•  The acquired scan data is selected for image reconstruction with respect to a pre-defined cardiac phase. 
•  Similar to ECG-triggered sequential scanning a certain R-wave delay time defines the start point of data that is used for image reconstruction. 
•  It has several advantages over ECG-triggered sequential scanning as the continuous acquisition allows for reconstruction of overlapping slices. But due to the retrospective analysis of the ECG, the technique is less sensitive to arrhythmia. 

Prospective ECG-triggered sequential scanning

• Cardiac CT applications require the synchronization of data acquisition to the cardiac cycle, i.e. to the movement of the heart. 
• For sequential imaging, a prospective trigger is derived from the ECG-trace to initiate the CT-scan with a certain delay time after the R-wave.
• The true delay time is calculated from a given phase parameter (e.g. a percentage of the RR-interval time) for each cardiac cycle individually based on a prospective estimation of the RR-intervals. 
• Usually, the delay is defined such that the scans are acquired during the diastolic phase of the heart.