Книги по МРТ КТ на английском языке / Thomas R., Connelly J., Burke C. - 100 cases in radiology - 2012

CASE 92: NORMAL VARIANT ON A CHEST RADIOGRAPH

History

Following her second year of foundation training, a 26-year-old junior doctor has decided to spend a year in Australia gaining further experience. Having successfully gained sponsorship by the Northern Sydney Central Coast Health Authority, she has to be certified medically fit by a recognized senior physician to comply with immigration policy. This involves completing a medical questionnaire, satisfying a medical examination, completing a series of screening blood tests and having a normal chest radiograph with no evidence of communicable disease.

She feels well and has no relevant past medical history. Other than being an occasional smoker there is no significant findings at history or physical examination.

Examination

Her blood results are as follows: white cell count (WCC) 9.4 × 109/L, Na 137 mmol/L, bilirubin 9 μmol/L, haemoglobin 11.6 g/dL, K 4.2 mmol/L, alanine aminotransferase (ALT) 27 IU/L, mean corpuscular volume (MCV) 78 fL, urea 4.1 mmol/L, alkaline phosphatase 146 IU/L, HIV negative, creatinine 87 μmol/L, albumin 41 g/L. Chest radiograph is shown in Figure 92.1.

Figure 92.1 Chest radiograph.

Questions

• What normal variant is found on this chest radiograph?

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ANSWER 92

Figure 92.1 is a chest radiograph of an adult female patient. It is not rotated and there is adequate penetration with optimal inspiratory effort made. The heart is of normal orientation and size (cardiothoracic ratio 30/12 cm), with both hilar correctly positioned with normal appearances. Cardiomediastinal assessment demonstrates a right-sided aortic arch. The lungs are clear and free from active disease. There is no evidence of old Mycobacterium tuberculosis exposure. Bone review is normal. There is no pneumothorax or evidence of free air under the diaphragm.

Normal aortic anatomy: The aorta is divided into the ascending thoracic aorta, arch of the aorta, descending thoracic aorta and abdominal aorta. The ascending aorta begins at the aortic root running superiorly and anteriorly, adjacent to the right side of the sternum. It is enclosed with the pulmonary trunk in a sheath of serous pericardium and is in continuation with the arch of the aorta. Lying behind the manubrium of the sternum, the aortic arch runs superiorly, posteriorly and from left to right anterior to the trachea. The arch gives rise to the brachiocephalic artery, left carotid artery and left subclavian artery as it runs across the mediastinum to become the descending thoracic aorta. This descends inferiorly as a posterior mediastinal structure, piercing the diaphragm at the level of the twelfth thoracic vertebra and is in continuity with the abdominal aorta.

A right aortic arch is an embryological variant with persistence of the right arch and right descending aorta while undergoing regression of the left side. Seen in approximately 2 per cent of the western population, its course within the chest is to the right of the trachea and oesophagus, crossing the midline in the lower thorax to pierce the diaphragm in the anatomically correct position. Its incidence increases in congenital heart disease (e.g. tetralogy of Fallot), and is commonly associated with one of three aberrant vascular anomalies:

•Right aortic arch with aberrant left subclavian artery: This is the commonest right aortic arch anomaly and is associated with cardiac septal defects and coarctation. The patient is usually asymptomatic but its positioning predisposes to aortic torsion in adulthood. The left carotid artery is the first branch of the aortic arch with an aberrant left subclavian artery arising from the proximal descending aorta.

•Right aortic arch with mirror image branching: As the second commonest right aortic arch anomaly, this is caused by embryological interruption of the arch between the left subclavian artery and the descending aorta, most commonly just distal to the ductus arteriosus. The great vessels branch opposite to the anatomicial norm, and patients are often symptomatic, being strongly associated with cyanotic heart disease (e.g. truncus arteriosus).

•Right aortic arch with isolated left subclavian artery: In this third most common scenario, the aortic arch is interrupted between the left common carotid artery and the left subclavian artery. The result is a left subclavian artery arising from the left pulmonary artery, and the patient is symptomatic with congenital subclavian steal syndrome.

A right aortic arch is a normal anatomical variant. Having survived into adulthood with no symptoms, it is highly unlikely that this incidental finding is of any clinical consequence. The student was passed fit to travel, and had a successful year in Australia.

KEY POINTS

•The normal aortic arch runs superiorly, posteriorly and from left to right anterior to the trachea.

•A right-sided aortic arch is seen in 2 per cent of the population.

•There are often concomitant aberrant vascular anomalies with a right-sided aortic arch.

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CASE 93: FLANK PAIN AND HAEMATURIA

History

An intravenous urogram (IVU) study is requested on a 41-year-old man who has presented with right flank pain. His symptoms started 3 days ago with a dull pain on his right side just below his ribs, which has remained constant and is not relieved by simple analgesia. He attended his local accident and emergency department last night as the pain woke him from sleep, and a presumptive diagnosis of a right-sided renal stone was made. He was placed on appropriate analgesia.

He had no relevant medical history until last year when he experienced an acute but short-lived pain on his left side while on holiday in Africa. Returning to the United Kingdom, his general practitioner (GP) retrospectively diagnosed a renal stone and investigations showed a slightly elevated serum calcium and parathyroid hormone level. He is currently being investigated for hypercalcaemia and further nuclear medicine studies are scheduled next month.

Examination

His results today demonstrate a deterioration in renal function (creatinine 320 μmol/L) compared to a normal baseline last month. His urine dipstick is positive for microscopic blood but free from white cells and protein. On examination he is more comfortable following analgesia, but there is a pain on deep palpation and a fullness to the right side of his abdomen compared to the left. The intravenous urograms are shown in Figure 93.1.

Figure 93.1 Intravenous urograms: (a) control; (b) 20 minutes post contrast.

Questions

•What does this IVU study demonstrate?

•What imaging modalities are available to characterize this type of problem?

•How should this patient be treated?

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ANSWER 93

These are two images from an IVU study. The control film (Figure 93.1a) demonstrates a solitary well-defined calcified focus measuring 12 mm overlying the right pelvico-ureteric junction (PUJ)/upper ureter. There is no other radio-opacity overlying the renal tracts and both kidneys appear of equal size and shape. Post intravenous contrast administration (Figure 93.1b) there is asymmetrical excretion of contrast, with normal appearances to the left kidney and ureter, but delayed excretion and a persistent nephrogram on the right. No contrast is seen within the right collecting system on the post-micturition 20-minute film, suggesting a partially obstructed right renal system.

On delayed imaging at 4 hours (Figure 93.2), there is excretion of contrast into a dilated pelvicocalyceal system, with the distal pelvis measuring approximately 11 mm. There is a faint trace of contrast seen within the right mid ureter, with additional contrast collecting in the bladder compared to the 20-minute post-micturition film. These findings are in keeping with a partially obstructed right renal system, most likely caused by a renal stone at the PUJ/proximal ureter.

Figure 93.2 Delayed imaging at 4 hours.

Nephrolithiasis is the most common cause of renal calcification with over 10 per cent of the western population developing a stone by the age of 70 years.1 The majority of renal stones (80 per cent) are made of calcium oxalate/calcium phosphate and are commonly associated with primary and secondary hypercalcaemia. The remaining renal stones have a mineral composition of either cystine or magnesium ammonium phosphate (struvite). Rarely, renal stones can be formed from either uric acid, xanthine or a mucopolysaccaride matrix, and it is important to remember this, as these stones are radiolucent and therefore radiologically invisible.

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Other than an IVU, other imaging modalities include:

•Ultrasound: The renal stone is highly echogenic against the grey renal parenchyma, with an acoustic shadow often projected deep to the stone. Ultrasound also carries a high sensitivity of detecting pelvicocalyceal dilatation and does not expose the patient to ionizing radiation. Its limiting factor is operator dependence. Small, non-obstruct- ing stones may be poorly visualized due to renal pelvis fat, which is also echogenic.

•Computed tomography (CT): Non-contrast CT-KUB (kidneys, ureter, bladder) is the gold standard and is highly sensitive for renal stone detection and characterization. The radiation dose is low and exam time is short (less than 5 minutes), with no risk of nephropathy as intravenous contrast is not required. Stone size, position and density can be assessed to guide treatment (e.g. lithotripsy or percutaneous nephrolithotomy (PCNL)). CT-KUB is replacing IVU as the preferred imaging modality for renal stone disease.

•Nuclear medicine: There is a limited role for both MAG3 and DTPA (diethylene triamine pentaacetic acid) studies in cases of nephrolithiasis, with the stone appearing as an area of photopenia on a background of homogeneous uptake. In an obstructed system the studies are more useful and can demonstrate renal perfusion abnormalities and can be used to compare the split function of both kidneys.

•Magnetic resonance imaging (MRI): This modality has no significant role in the diagnosis of renal stone disease but may do in the future.

In this patient, an obstructed right renal system and deteriorating renal function needs to have definitive treatment to decompress the renal pelvis and preserve right kidney function. Options include a percutaneous nephrostomy inserted under fluoroscopy guidance by the interventional radiologists (see Case 71). However, the nephrostomy drainage catheter can only remain in place for a limited time and this procedure carries risks of infection and bleeding. The preferred alternative is a ureteric stent which can be placed in a retrograde fashion during cystoscopy over a guidewire. The ‘double-J’ stents have multiple perforations and can bypass the stone, allowing pelvicocalyceal decompression. The ureteric stent can remain in place for up to 3 months while a definitive decision on stone removal is made, and is then easily removed during a repeat cystoscopy procedure when necessary (Figure 93.3).

Figure 93.3 Ureteric stent in place.

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CASE 94: PATIENT WITH AN INTRACTABLE HEADACHE

History

A 42-year-old woman is bought to the accident and emergency department by her husband complaining of headache. Her symptoms started a few hours earlier with the sudden onset of sharp stabbing pain at the back of her head. This rapidly progressed and soon became the worst headache she had ever had. Despite simple analgesia and rest, the headache did not subside and the pain caused her to vomit several times. There has been no altered consciousness but her husband was concerned by her restlessness and agitation, and brought her to hospital.

The patient has a past medical history of asthma, which is well controlled on inhalers provided by her general practitioner (GP). She also has annual review with the hospital nephrologists for a history of polycystic kidney disease.

Examination

She is irritable and looks unwell. She is hypertensive (170/110) and has a regular pulse of 105 beats per minute. There is neck stiffness, and worsening of her headache on straight leg raising but no focal neurology. Ophthalmoscopy is not tolerated and the patient asks you to turn the lights off as they are hurting her eyes. A computed tomography (CT) scan was performed (Figure 94.1).

Figure 94.1 Unenhanced axial CT scan.

Questions

•What does the CT scan demonstrate?

•Why was this patient at increased risk?

•What would you do if the CT scan had been normal?

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ANSWER 94

This image is a single slice from an unenhanced CT scan taken at the level of the basal ganglia. There is widespread abnormal high attenuation with a gyriform distribution within both cerebral hemispheres. This high attenuation material is denser than adjacent brain parenchyma but less dense than bone and represents acute blood. In the image, arrows demonstrate acute blood replacing CSF within the Sylvian fissure (white arrow) and quadrigeminal cistern (black arrow). There is mass effect with sulcal effacement and the lateral/third ventricles are prominent in keeping with hydrocephalus. Some acute blood is seen within the third ventricle at the expected origin of the aqueduct of Sylvius. This patient has therefore suffered an acute subarachnoid haemorrhage (SAH) with hydrocephalus.

Subarachnoid haemorrhage is defined as blood collected between the pia and arachnoid mater. Clinically, patients with an SAH commonly present with an acute severe occipital headache (‘thunderclap’) with associated vomiting, altered conscious state and agitation. Unenhanced cranial CT demonstrates acute blood (white – HU 60–70) within the cerebrospinal fluid (CSF) spaces. Large haemorrhages can be easily seen, but smaller bleeds can be more difficult.

Causes of SAH include:

•ruptured aneurysm,

•AV malformation,

•hypertensive haemorrhage,

•haemorrhage from tumour,

•intracranial infection,

•blood dyscrasias, and

•anticoagulation.

Adult polycystic kidney disease (APKD) is an autosomal dominant genetic condition, which is slow to progress but has 100 per cent penetration in the affected individual. Multiple thin-walled cysts form within native kidneys. Commonly causing pain, haematuria and proteinuria, unrestricted cyst growth replaces normal renal parenchyma, eventually causing renal failure. The patient is also at increased risk of developing renal cell carcinoma. APKD has associations with cysts in other organs (e.g. liver and pancreas), mitral valve prolapse and saccular ‘berry’ aneurysms of the cerebral arteries (3–13 per cent).1 These aneurysms tend to be multifocal and rupture of any aneurysm causes blood to leak into the subarachnoid space and SAH.

If the CT scan in a patient with this suspicious history had been normal, a lumbar puncture would need to be considered as a normal cranial CT does not exclude small SAH (sensitivity 90 per cent).1 Lumbar puncture is essential to confirm the presence of normal or altered blood (xanthochromia) within the circulating CSF that bathes the brain. Any blood in the CSF space can cause obstruction and put the patient at risk of communi- cating/non-communicating hydrocephalus and death. Clinicians often feel reassured by requesting a cranial CT to exclude the absolute contraindication of raised intracranial pressure (ICP) before lumbar puncture to reduce the risk of ‘coning.’ However, cranial CT is not a sensitive exclusion modality,2 and full clinical assessment looking for the stigmata of raised ICP would be advised.

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