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

lower dose ventilation/perfusion (V/Q) study may diagnose a pulmonary embolism rather than a CT chest.

KEY POINTS

•Formal chest radiographs are acquired in a posterior–anterior (PA) orientation.

•The silhouette sign can accurately locate pathology to a particular lung lobe.

•Always consider radiation dose to the patient when requesting a radiological procedure.

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CASE 87: TRAUMATIC INJURY TO A FARMER’S FOOT

History

A 45-year-old farm worker is bought to hospital by his wife. While changing the wheel of his tractor earlier today, the jack collapsed and the tyre landed on his left foot before rolling off. He felt an immediate sharp and stabbing pain which was exacerbated by walking. His foot began to swell despite ice and elevation. Worried that he may have fractured a bone they attended the minor injuries unit that evening.

He has no relevant past medical history but is a smoker of 20 pack-years.

Examination

Examination reveals a swollen left foot with bruising centred on the plantar arch. The patient is in continued discomfort, with the medial aspect of the foot being most tender over the first metatarsal. He is sent for a foot radiograph before further management is planned (Figure 87.1).

Questions

• What injury does this radiograph show?

• What joint and ligament is involved?

• Why is it important to recognize this injury?

Figure 87.1 Anterior–posterior (AP) radiograph of foot.

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ANSWER 87

In a normal anterior–posterior (AP) radiograph of a foot, the medial aspect of the second metatarsal should align with the medial margin of the middle cuneiform. Figure 87.1 demonstrates an AP weight-bearing radiograph of the left foot. There is malalignment of the Lisfranc joint, with a homolateral 3 mm slip of the second to fifth metatarsals. No obvious fracture is seen and the remaining bones of the midand forefoot are intact and correctly located. These features are in keeping with a Lisfranc dislocation, and the patient should be referred to orthopaedics for further management.

The Lisfranc joint separates the bones of the midfoot, comprising the cuneiform and cuboid bones, from the metatarsals of the forefoot. Each cuneiform bone articulates with its first, second and third metatarsal, respectively, with the fourth and fifth metatarsals articulating with the cuboid bone. Stability of the joint is maintained by complex ligaments found on the plantar surface, which maintain alignment when weight-bearing. These ligaments are subject to significant shear forces on every step a person takes, and are put under increased pressure in athletes. The largest ligament is the Lisfranc ligament, which originates from the lateral aspect of the medial cuneiform bone, and inserts into the medial aspect of the second metatarsal. It is primarily responsible for stability of the whole joint, and maintains the plantar arch while preventing the second to fifth metatarsals slipping laterally when walking.

Following injury, the Lisfranc ligament may either be stretched (Lisfranc sprain) or completely torn. Joint stability and alignment is lost, causing diastasis between the first and second metatarsals and dislocation of the Lisfranc joint. Patients present acutely with soft tissue swelling, plantar bruising and pain on weight-bearing. Special attention should be given to those patients with sensory peripheral neuropathy (e.g. alcoholics and diabetics).

The injury is sustained either through longstanding repetitive strain placed upon the ligament (e.g. athletes), or from a direct axial load forcing the foot downwards while in rotation. The latter is often associated with bone fractures in combination with Lisfranc dislocation. When suspected, a patient should be referred for orthopaedic assessment with further imaging in the form of computed tomography (CT) to look for associated fractures (Figure 87.2), and magnetic resonance imaging (MRI) to assess ligament integrity. Without correction, normal biomechanics of the foot are lost, and the patient will develop irreversible osteoarthritic change with eventual incapacitating disability on a background of chronic pain.

Figure 87.2 Unenhanced coronal CT image with bone windowing showing a bony fragment in between the first and second metatarsal bases indicative of a Lisfranc ligament rupture.

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Treatment differs between institutions and is determined by joint stability. In a sprain where the Lisfranc ligament is intact, treatment is conservative with the foot immobilized in a cast for 6 weeks. When the joint is unstable, surgery is required with the insertion of screws and wires necessary to maintain reduction. The foot is immobilized in a cast, and the patient is non-weight-bearing for 3 months. The screws are eventually removed following satisfactory healing with clinical outcome dependent on restoration of normal alignment.

KEY POINTS

•Bony misalignment can indicate ligamentous injury in the absence of bony injury.

•Two views of a bony joint, preferably at right angles to each other, should always be acquired.

•Patients should be referred for an MRI or CT scan if there is suspicion of bony/ ligamentous injury.

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CASE 88: AN ACCOUNTANT WITH ABDOMINAL PAIN

History

A 37-year-old accountant has been referred to your outpatient clinic by his general practitioner (GP). He complains of vague abdominal discomfort, which is central, colicky and intermittent. He has been having these symptoms for as long as he can remember and was thought to have irritable bowel syndrome. They have recently been increasing in frequency and his new GP decided to investigate them further. There are no predisposing factors and he has tried several dietary changes with no resolution of symptoms. He denies any weight loss, change in bowel habit or vomiting, but suffered attacks on a weekly basis now. The pain subsides spontaneously after a few hours with no sequelae.

There is no relevant past medical history. He does not take any regular medication and denies allergy. He is a non-smoker, does regular exercise and lives with his wife and child.

Examination

Nothing abnormal was found on examination. A set of blood results taken last month are normal, and he has recently had a barium follow-through investigation (Figure 88.1).

Figure 88.1 AP image from barium follow-through study.

Questions

•Describe the barium study.

•What is the abnormality demonstrated?

•What are the complications of this condition?

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ANSWER 88

This is a single anterior–posterior (AP) image from a barium follow-through study, centred on the abdomen and pelvis. There is good contrast opacification of the stomach with normal distended appearances and no evidence of a filling defect. Barium is seen to pass freely into the duodenum and jejunum on this 15-minute film, with no evidence of stricture or obstruction. The pylorus and proximal duodenum are seen in the expected position, but the opacified distal duodenum fails to cross the midline, instead remaining on the right of the abdomen. The duodenal–jejunal (DJ) junction is abnormally located within the right upper quadrant, with opacified jejunum appearing to continue on the right side. Delayed images are required to see the position of the remaining small bowel and caecal pole.

Figure 88.2 shows an image from the same patient taken at 80 minutes following ingestion of barium and demonstrated continuation of the entire small bowel to the right of the midline. There is no evidence of stricture or obstruction. The caecal pole is located within the pelvis, but is medial to its expected position in the right iliac fossa. The hepatic flexure is abnormally positioned and lies within the left upper quadrant, with the entire large bowel seen to lie on the left side of the abdomen. These features indicate a diagnosis of malrotation.

Figure 88.2 Subsequent image from barium follow-through.

During embryological development the primitive midand hindgut move out of the abdominal cavity and normally rotate 270 degrees anticlockwise on a mesentery around the central omphalomesenteric axis. This twisting movement allows the gut to pass under the primitive superior mesenteric vessels as they form, before re-entering the abdomen. The DJ flexure is then fixed to the base of the left hemidiaphragm by the ligament of Treitz, and the caecal pole is secured in the right lower quadrant.

If the primitive gut is secured to a mesentry that is shorter than usual, the gut cannot complete its full rotation, leaving the caceal pole and DJ junction in anatomically abnormal positions. This is termed ‘malrotation’, and is best diagnosed with a barium follow-

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through study, to identify the abnormal peritoneal fixation from the position of the bowel loops. On a CT scan, the position of the superior mesenteric vessels is reversed, with the superior mesenteric artery (SMA) positioned to the right of the superior mesenteric vein (SMV). Imaging studies demonstrate a variety of appearances depending on how much of the 270 degrees the bowel rotated before fixation, with a right-sided duodenum and jejunum being the commonest finding. Patients are often symptomatic as neonates and children, suffering from recurrent abdominal pain, distension and vomiting. Failure of the primitive gut to rotate at all results in the entire small bowel on the right side of the abdomen with the large bowel on the left, as in this case. These patients with nonrotation often present as adults, and describe a history of mild intermittent abdominal pain for as long as they can remember.

A short mesentry predisposes children to the complication of midgut volvulus. Most commonly presenting in the first 3 weeks of life, children present with bilious projectile vomiting and abdominal pain. This is a medial emergency and can lead to bowel infarction and death. Its characteristic features on a barium study demonstrate malrotation with a spiralling ‘corkscrew’ appearance to the bowel distal to the obstruction (Figure 88.3).

Figure 88.3 Midgut volvulus.

KEY POINTS

•Oral contrast fluoroscopy studies have a high sensitivity for detecting malrotation.

•Normal embryological development involves a 270 degree anticlockwise rotation around a central omphalomesenteric axis.

•On CT scans, check the position of the SMA in relation to the SMV in cases of suspected malrotation.

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CASE 89: PAIN IN A WOMAN WITH BREAST CANCER

History

A 57-year-old woman attends the hospital for a computed tomography (CT) scan. She was diagnosed with breast cancer 3 years previously and was successfully treated with a right mastectomy, radiotherapy and chemotherapy. Following breast reconstruction last year, a routine CT scan demonstrated no assessable disease and the patient was offered a clinic appointment for 6 months’ time. Recently she has noticed some increasing pain the right upper quadrant of her abdomen and reported unexpected weight loss of over 2 kg. Informing her hospital consultant via telephone, the patient was asked to attend hospital for a blood test and repeat CT scan of the chest and abdomen. She is due to see the consultant in clinic tomorrow.

Examination

On the CT scan you find evidence of post-surgical change within the reconstructed right breast with no assessable disease above the diaphragm. Abdominal review demonstrates multiple areas of low attenuation within the liver, which are new compared to the previous CT, in keeping with hepatic metastases. Both kidneys are unobstructed and there is no evidence of portal vein thrombosis. To complete the report, you review the bony skeleton reconstructed in the sagittal plane for improved image interpretation (Figure 89.1).

Figure 89.1 Sagittal reconstruction from a CT scan.

Questions

•What does the CT scan demonstrate?

•What are the common tumour types that cause this appearance?

•What further radiographic investigations should be considered?

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