• Retinoblastoma ;is the most common tumour of the globe in children. It occurs in children less than 3 years of age presenting with leukokoria. It derives from primitive photoreceptors or neuronal retinal cells, and histologically resembles other primitive neuroectodermal tumoursCT is the preferred method to image the child with leukokoria because it is sensitive to calcification in retinoblastoma. CT demonstrates clumped or punctate calcification (in 95 per cent of cases) in the posterior part of the globe extending into the vitreous, with minimal enhancement. In advanced cases the tumour may fill the globe ,OFthese tumours, 75 per cent are unilateral unifocal and 25 per cent are bilateral or unilateral multifocal. When it is found bilaterally and in conjunction with a pineoblastoma, it is labelled ‘trilateral retinoblastoma’; 10–40 per cent are familial (autosomal dominant, and these tumours tend to be bilateral and associated with other nonocular tumours

• Uveal melanoma is the most common primary intra-ocular malignancy in adults. The great majority are located unilaterally in the choroid. It can metastasize to the liver and lung. Diagnosis is usually performed on ophthalmoscopy and ultrasound

• Cavernous haemangioma is the most common orbital tumour. These lesions occur in adults 20–40 years of age and in men more than women. They present with proptosis, but vision is usually unaffected. CT and MRI usually show a sharply demarcated, rounded or oval mass that spares the orbital apex

• Optic nerve meningiomas occur in middle-aged women, and more rarely in children with neurofibromatosis type 2. They are the second commonest primary tumours of the optic nerve after gliomas [these lesions are hyperdense on CT and also enhance strongly they produce a ‘tram track’ sign on axial images and a ‘doughnut sign’ on coronal images

• Ooptic nerve gliomas are childhood slow-growing low-grade pilocytic astrocytomas, with 75 per cent of cases occurring at less than 10 years of aThese lesions result in tortuous thickening of the optic nerve/sheath complex that is most commonly tubular, but may also be fusiform or excrescent.

• Rhabdomyosarcoma is one of the more common primary malignant tumours of the orbit in children aged 2–5 years. Orbital rhabdomyosarcoma is the most common site of head and neck rhabdomyosarcoma. On CT, these bulky aggressive-looking masses are isodense or slightly hyperdense, and show uniform enhancement On MRI they are of intermediate signal intensity on both T1 and T2 sequences. There is bone destruction in 40 per cent of cases and frequent distortion of the globe.

• ORBITAL INFECTION IMAGING ;more serious orbital postseptal infection can arise from sinus disease, bacteraemia, trauma, or spread of a serious infection from the skin. On CT and MRI this is seen as ill-defined tissue planes in retrobulbar structures, loss of the normal hyperintense signal of orbital fat on MRI, with or without a soft tissue mass. The latter may demonstrate ring enhancement and/or pockets of gas suggestive of abscess formation

• Blunt trauma may uncommonly result in globe rupture or laceration, which is usually evident by loss of the normal globe contour on CT or MRI; dislocation of the lens may also be seen in these cases. More commonly, blunt trauma results in retinal or choroidal detachments.

Scrotal condition• Hydrocele A hydrocele is the formation of fluid

between the twolayers (visceral and parietal) of the tunica vaginalis

• Cysts Simple cysts are extremely common in the scrotum. Theymay be seen at any age from adolescence onwards but are mostcommon in the elderly. The majority are seen in the epididymis.particularly in the upper pole

• Varicocele Dilatation of the network of veins draining the testiclei s described as a varicocele. They are extremely common (up to8-16% of the male population), and usually asymptomatic, oftenbeingeOn ultrasound varicoceles are seen as a leash of predominantlyecho-free serpiginous structures measuring more than 2 mm

• maximum diameterThe vast majority of varicoceles are described as primary and arepresumed to be due to developmental abnormalities of the valvesand/or the veins themselves. This is far more likely on the left,where at least 95% are encountered. A minority occur secondary to

• a lesion compressing or occluding the testicular vein. The classicalcause is a left-sided renal cell carcinoma extending along the renalvein as far as the termination of the testicular vein, There is a higher risk of an underlying cause, particularly a tumour if the varicocele is of recent onset with an acute presentation,the patient is older than 40 years, it is right-sidedand isunchanged with provocative manoeuvres.

• testicular torsion; peaks in peripubertal boys but there is a smaller peak in infancyAcute torsion has been defined as lasting from 24 h to 10 d. Thereafter the torsion is considered to be subacute, and then chronic. Other classifications define torsion of greater than 24 h duration as missed torsion. Testicular salvage rates are closely related to time to diagnosis. Salvage rates of 80 per cent in the first 6 h drop to 20 per cent if surgery is delayed for 24 h[37]. The US appearances include an enlarged heterogeneous testis and epididymis in the acute phase[Colour Doppler studies have resulted in an improvement in the US evaluation of testicular torsion with a claimed sensitivity and specificity of 100 per cent Testicular torsion is diagnosed when blood flow in the symptomatic testis is absent or markedly reduced compared with the normal side

• Acute epididymitisOn US the entire epididymis may be enlarged but occasionally only the head. The epididymal reflectivity may be heterogeneous but is usually of lower reflectivity than normal[25]. Colour Doppler US studies have been shown to be useful in differentiating epididymis and orchitis from other causes of acute scrotal pain, in particular testicular torsion. All cases of acute epididymitis demonstrated an increase in colour flow. None of the cases of scrotal pain without epididymitis demonstrated this finding[

• Testicular malignancies i primary testicular germ cell tumours, non-germ cell tumours, metastases, lymphoma and adrenal rest tumours.

• Approximately 95 per cent of primary testicular tumours are of germ cell origin, the remainder arising from Leydig, Sertoli or theca cells that comprise the gonadal stroma. Most germ cell tumours are of single histological type and are seminomas. In order of frequency, other histological types comprise embryonal tumours, yolk sac tumours and teratomas. Approximately 40 per cent of tumours are of mixed cellularity. The peak incidence of seminoma is in the 4th and 5th decades while the incidence of other germ cell tumours peaks approximately a decade earlier. All testicular tumours are rare in childhood, where yolk sac tumours, followed by teratomas, are the most common. Seminomas are generally extremely radiosensitive; they are associated with high levels of alphafetoprotein (AFP) Teratomas respond well to a number of chemotherapeutic agents and are associated with elevated AFP and hCG. They are characteristically less responsive to radiotherapy. The differentiation of seminoma from the other histological types is important clinically but, despite some variation in the ‘textbook’ appearances, there are generally insufficient features to make the distinction using direct imaging or Doppler features. Seminomas are characteristically hyporeflective compared with the surrounding parenchyma and are well-defined and homogeneous ,they may also be apparently multifocal on presentation.

• The thyroid gland is located in the anterior part of the neck with the lateral lobes lying on either side of the trachea joined across the midline by the isthmus. Each lobe measures approximately 40 × 20 × 20 mm. Ultrasound (US) provides the best anatomical representation of the thyroid gland. Using high-resolution (7.5–10 MHz) probes, modern machines provide excellent spatial resolution and allow nodules as small as 2–3 mm to be detected.

• Thyroid nodules • One of the most common clinical problems is in patients presenting with a

solitary palpable thyroid nodule. Its importance is due to the fact that thyroid cancer most often presents as a solitary thyroid nodule. However, thyroid nodules are extremely common. The majority are benign, due to cysts, thyroiditis, adenomas, or colloid nodules. Investigation is directed towards detecting the 5–10% of palpable thyroid nodules that are malignant[12]. US cannot reliably distinguish between benign and malignant thyroid nodules, but is however extremely effective in distinguishing between solid and cystic lesions. Purely cystic lesions with no soft tissue component are very rarely cancers, and in most institutions are managed with fine-needle aspiration. Certain US features increase the likelihood of malignancy of a thyroid nodule; notably, invasion into surrounding tissues, which results in loss of clear definition of the tissue planes. US is more sensitive than clinical examination in the detection of enlarged cervical nodes. Cervical lymph nodes, infiltrated by papillary carcinoma of the thyroid, may be entirely cystic , while calcification may be seen within nodes invaded by medullary carcinoma. Microcalcification smaller than 2 mm in diameter with acoustic shadowing suggests malignancy, as it is observed in about 60% of carcinomas but only 2% of benign nodules[14].

• Ultrasound-guided fine-needle aspiration for cytology (FNAC) is the most reliable nonoperative method for obtaining a definitive diagnosis and is important in the selection of patients for surgery. Overall, the sensitivity of FNAC for the detection of malignancy in both cystic and solid lesions ranged from 90 to 100%. However, false-positives occur quite frequently, so the specificity is only 55% for solid nodules and 52% for cystic lesions [15