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

ANSWER 89

This image is a sagittal reconstruction from a CT scan centred on the lower thoracic, lumbar and sacral spine. It has been windowed to improve bony resolution. It demonstrates multiple areas of well-defined reduced attenuation and loss of the normal bony architecture throughout the vertebral column and sacrum with evidence of posterior element involvement. They have a narrow zone of transition and are surrounded by areas of ill-defined sclerosis. The vertebral column retains a normal alignment and there is no loss of vertebral body height to suggest vertebral collapse. Within the limits of this single image, the cord appears capacious throughout, although review of the whole image series is recommended. The findings are in keeping with multilevel lytic bone metastases.

Secondary bone deposits are approximately 100 times more common than primary bone tumours.1 Spread from the tumour haematogenously, via the lymphatics or through direct invasion, they have a predilection for parts of the skeleton with high marrow content, affecting the axial skeleton more often than the ribs and skull. Their presence alters the bone integrity, and patients are at increased risk of fracture despite normal physiological loads being applied, known as ‘pathological fractures’. This is most marked in the spine, where vertebral compression fractures can cause spinal canal stenosis from retropulsed bone fragments, which can encroach on the spinal cord causing compression and neurological compromise. Spinal cord compression is a neurosurgical emergency.

Depending on cell type, tumour deposits upregulate either osteoclastic or osteoblastic activity, giving characteristic radiographic appearances. Those metastases with osteoclastic activity cause bone lysis, with soft tissue deposits destroying the adjacent bone and reducing the structural integrity. On X-ray, the bone can appear ‘moth-eaten’ and destroyed, with pain being the commonest clinical symptom. Osteoblastic metastases cause bone sclerosis, with new bone formation appearing as areas of increased density. The involved bones retain their normal morphology, but the heterotrophic bone has abnormal trabecular architecture, reducing the overall bone integrity. To confuse matters, some tumour types have metastases with both lytic and sclerotic components, and lytic bone metastases become sclerotic following treatment (e.g. radiotherapy or chemotherapy). A few metastases can also cause characteristic bone expansion and the common appearances are listed in Table 89.1.

Table 89.1 Common tumour appearances

Bone metastases are more likely to be multiple than solitary, and a combination of modalities such as plain X-ray, CT and MRI are used to assess bony metastatic disease. Bone scintigraphy, where radioactive phosphate particles are administered intravenously, is often appropriate in characterization of disease distribution and treatment response.

262

The whole body is imaged, and the normal physiological bone appearances are disturbed by areas of intense tracer uptake from sclerosis, or areas of photopenia from bone lysis. It is highly sensitive with relatively low radiation exposure, and is useful to localize areas of possible disease for further assessment.

Figure 89.2 shows a bone scintigraphy study from a patient with a prostate specific antigen (PSA) of >2000, with increased tracer uptake seen in the skull, both shoulders, shaft of both humeri and femora. There is also diffuse uptake of tracer noted in multiple ribs bilaterally as well as in multiple vertebrae at multiple levels. The proximal tibia, pelvis and right sterno-clavicular joints are also involved. Both kidneys are not visualized suggesting a ‘superscan’ consistent with extensive bone metastases from an underlying diagnosis of prostate cancer.

Figure 89.2 Bone scintigraphy images.

KEY POINTS

•Bone metastases can be either lytic, sclerotic or mixed

•CT has a high sensitivity for resolving bony abnormality.

•Bone scintigraphy can be employed to assess the extent of bone involvement.

Reference

1.Dahnert, W. (2011) Radiology Review Manual, 7th edn. Philadelphia: Lippincott Williams and Wilkins.

263

CASE 90: HEADACHE AND VISUAL FIELD DEFECTS

History

A 48-year-old man has been referred by his general practitioner (GP) for further management. He complains of weight gain, tiredness and headache over the last few months with no resolution of symptoms despite diet and analgesia. Initially thought to be stress related, a screening blood test revealed normal biochemical markers other than a slightly low T4, low thyroid stimulating hormone (TSH) and low testosterone.

There is no relevant medical history. He is not taking regular medication and is a nonsmoker. Living at home with his wife and children, he has taken several sick days recently because of his symptoms.

Examination

Examination reveals a tired looking Caucasian man in no obvious discomfort. His body mass index (BMI) is 26 (previously recorded at 23). He is afebrile, normotensive and with a regular pulse of 56 beats per minute. Cardiovascular, respiratory and abdominal examination is normal. On neurological examination, visual field assessment reveals a bitemporal hemianopia. A thyroid ultrasound scan and chest radiograph were normal, and a cranial computed tomography (CT) scan was arranged (Figures 90.1 and 90.2).

Questions

•What does the CT scan show?

•Is there a differential for these appearances and what would you do next?

•What is the cause of the patient’s symptoms and biochemical abnormality?

265

ANSWER 90

The two images of the same patient are taken from a cranial CT study before and after the infusion of intravenous contrast. The axial image (Figure 90.1) is unenhanced and acquired at the level of the cavernous sinus. The patient’s head is slightly tilted to the right. Within the suprasellar space there is a soft tissue mass measuring approximately 20 × 17 mm which is well defined and isodense to the neighbouring brain tissue. It is of homogenous attenuation and displays curvilinear rim calcification. It is expanding the sellar turcica and splaying the cavernous sinus laterally. There is normal grey/white differentiation and no evidence of acute haemorrhage. The second image (Figure 90.2) is taken following the infusion of intravenous contrast and reformatted in the coronal plane. The soft tissue mass demonstrates avid uniform enhancement centred on the pituitary fossa with suprasellar extension towards the optic chiasm and third ventricle. The sella is expanded as before but there is no obvious breach of the sella floor or extension into the sphenoid sinus. Within the limits of these images, the basal cisterns are preserved throughout and there is no evidence of hydrocephalus or tentorial herniation.

The differential for a pituitary mass with suprasellar extension includes:

•pituitary adenoma;

•carotid artery aneurysm;

•meningioma;

•pituitary metastasis;

•pituitary lymphoma;

•pituitary abscess;

•Rathke’s cleft cyst.

From this differential list, pituitary abscess and Rathke’s cleft cyst can be discounted as the pituitary mass is of homogeneous soft tissue density and the patient is not clinically septic or unwell. Pituitary metastasis and lymphoma are very rare and would be an unlikely diagnosis considering there are no other systemic symptoms. The patient should undergo magnetic resonance imaging (MRI) to characterize the mass further, with neurology/neurosurgery referral for outpatient follow-up (Figure 90.3).

Compressed optic chiasm

Figure 90.3 T1-weighted gadoliniumenhanced coronal MRI image demonstrating an enhancing pituitary mass lesion with suprasellar extension. The arrow highlights the compression of the optic chiasm. This requires urgent surgical attention so as to preserve vision.

266

This patient has a pituitary adenoma, which is a slow growing tumour of the anterior pituitary gland. Despite being benign, patients are frequently symptomatic depending on its size and functioning status. Pituitary adenomas are classified into macroor microadenomas. Patients with pituitary microadenomas (<10 mm) often present with symptoms of hormonal imbalance resulting from functionally active tumours, most commonly prolactin secreting with symptoms of amenorrhoea and infertility; instability of the adrenocortical, somatostatin and gonadotrophin axis can also occur.

In this case, the patient has a pituitary macroadenoma (>10 mm) with symptoms resulting from mass effect related to tumour bulk. Compression of normal pituitary tissue by tumour has resulted in loss of TSH secretion and a clinically hypothyroid patient. In addition, suprasellar tumour extension is causing compression of the optic chiasm and stretching of the prechiasmic optic nerve. This is highlighted on the MRI study and is the cause of the bitemporal hemianopia. With no intervention, the tumour will continue to grow and he will be at risk of visual loss, obstructive hydrocephalus and carotid artery involvement. This patient was referred to neurosurgery with successful tumour removal and complete symptom resolution.

KEY POINTS

•The suprasellar space should be a review area when viewing unenhanced CT images.

•The use of intravenous contrast improves diagnostic interpretation.

•Always looks for optic chiasm compression in suprasellar masses.

267

CASE 91: A CLAUDICANT WITH WORSENING LEG PAIN

History

A 71-year-old man is referred to the vascular surgical team with right leg pain. He is known to suffer from atherosclerotic peripheral vascular disease and is currently being treated conservatively for claudication. The pain in his right leg started suddenly 3 hours previously, with an achy discomfort that is not relieved by simple analgesia or positioning. Limited by pain, his mobility has reduced to only a few steps, and he reports increasing discoloration of his right foot compared to the left.

His relevant medical history includes type 2 diabetes mellitus, hypertension and angina. He is an ex-smoker of 40 pack-years. His drug history includes aspirin, metformin, isosorbide mononitrate and a calcium channel blocker. He takes sublingual glyceryl trinitrate as required.

Examination

Having been treated by the accident and emergency department for his pain, examination reveals a mottled right foot and reduced popliteal and pedal pulses compared to the left side. Femoral pulses are symmetrical and strong bilaterally, with no evidence of an expansile pulsatile abdominal mass. A computed tomography (CT) angiogram is performed which suggests a right common femoral stenosis, and the interventional radiologists are approached for advice (Figure 91.1).

Figure 91.1 Lower limb angiogram.

Questions

•What type of study is this and what does it show?

•What treatment options are available in this case?

•What factors need to be considered when using radiographic contrast agents?

269

ANSWER 91

Figure 91.1 is a single view acquired during an angiogram of the lower limbs. It is a procedure performed by the interventional radiologists on a fluoroscopy table, with the patient in the supine position. With a sterile technique, a needle is passed into the common femoral artery (CFA) under ultrasound guidance and subcutaneous local anaesthetic cover. In this case, a retrograde puncture of the left side was made to image the arteries of both legs, however an antegrade puncture technique is sometimes preferable in certain situations. Adopting the Seldinger technique, a guidewire is passed via the puncture needle into the aorta, and this is used to railroad a sheath and ‘pigtail’ multihole catheter. Positioning the catheter at the aortic bifurcation, 15 mL of contrast is pumped at 8 mL/s with digital subtraction images acquired of the opacified lower limb arteries.

A short tight stenosis of the mid superficial femoral artery on the right side is demonstrated, with the artery narrowed by approximately 80 per cent by a flow-limiting atherosclerotic plaque. There is a paucity of collateral vessels suggesting an acute obstruction. There is good run-off of the distal vessels. Both superficial femoral arteries demonstrate a background of mild atherosclerotic calcification.

Although surgery in the form of endarterectomy or bypass could relieve this stenosis, an open operation would carry significant risk and leave the patient with a visible scar. An endovascular repair through the left CFA puncture is preferable, leaving the patient with only a small pinhole scar in the groin and conserving the tissues of the right leg.

Crossing the aortic bifurcation, the stenosis can be transgressed with an atraumatic hydrophilic guidewire. This can then guide the passage of a balloon-mounted bare metal stent to the level of the stenosis. Balloon inflation (Figure 91.2) compresses the atherosclerotic plaque and delivers the stent to exert radial force and maintain continued patency long term (Figure 91.3).

The post-procedure angiogram (Figure 91.4) reveals a good response to treatment with improved blood flow to aid symptomatic relief. The sheath and catheter are removed and haemostasis of the groin achieved by manual compression. The patient will require dual antiplatelet therapy to aid stent patency.

Radiographic contrast media is used in all aspects of radiology to enhance tissue contrast and improve diagnostic interpretation. Barium, water and air can all be used in certain examinations (e.g. barium enema) but this is not suitable for intravenous usage in CT and angiographic studies. Iodine, with its high atomic number, has strong photoelectric X-ray absorption characteristics that make it ideal for use in intravenous contrast media. Injecting a predefined volume and imaging at a specific time allows for tissue enhancement characteristics to be determined and improves the contrast between soft tissues (Figure 91.4).

Before referring a patient for a study that involves the use of iodinated contrast, certain parameters need to be checked. There are documented allergies to contrast media, and also potential crossover in sensitive atopic individuals with shellfish and certain fruits (e.g. strawberries). Contrast media is predominantly renally excreted and patients require a degree of endogenous renal function to clear the injected contrast load. Intravenous contrast is also nephrotoxic and can precipitate renal failure in predisposed patients. It is important, therefore, to check a patient’s renal function prior to imaging to alleviate this potential risk. Adequate hydration before and after the use of intravenous contrast media is also recommended.

270

KEY POINTS

•Always review all imaging available before proceeding with an interventional procedure.

•Stent insertion is avoided if possible at areas of flexion to avoid stent kinking.

•Always check a patient’s renal function before initiating the use of intravenous contrast.

271