Hypertrophic Pulmonary Osteoarthropathy (HPOA)

Bone scan image shows diffuse increased uptake along the periosteum/cortical margins of both tibias (arrows), sparing the epiphysis, in this patient with lung cancer.

Facts: HPOA

• Clinical syndrome that includes clubbing of fingers/toes, periostitis of tubular bones of extremities and arthritis
• Originally described in association with pulmonary lesions
• Most commonly associated with pulmonary tumors (10% of cases)
• Patients can be asymptomatic or present with arthralgia, arthritis or bone pain
• Histopathology shows edema, mononuclear infiltrates and later osteoid formation of the periosteum
• Commonly involves long bones of forearms and legs, spared axial skeleton and skull

Imaging

• Symmetric periostitis along bony shafts, confined to diaphysis; do not involve joint
• Regular and undulating periosteal reaction
• On bone scan, there is diffuse increased uptake along the periosteum or cortical margins of long bones with sparing of epiphysis

Disorders Described with HPOA

• Pulmonary: cancer, metastasis, mesothelioma, infection and bronchiectasis
• Mediastinum: thymic cancer, thyroid cancer, esophageal leiomyoma, Hodgkin's disease
• Heart: cyanotic heart disease, bacterial endocarditis
• Others: liver cirrhosis, inflammatory bowel disease

Reference:

Vigorita VJ, Ghelman B, Mintz D. Orthopaedic Pathology, 2nd edition, 2007.

Carotid Cavernous Fistula (CCF)

The author would like to thank Drs Thanwa Sudsang and Tom Osborne for helping with labeling the vessels in these angiographic images.

AP and lateral views of the right carotid artery injection show simultaneous opacification of venous structures (superior/inferior ophthalmic veins, middle cerebral vein) and dilatation of the veins due to the presence of CCF in this patient who had recent head trauma.

Facts: CCF

• Rent in the wall of cavernous carotid artery with fistulous communication to the venous spaces of the cavernous sinus
• Either due to trauma (post-traumatic CCF) or ruptured cavernous carotid artery aneurysm
• Traumatic CCF typically seen in young adult male, post motor vehicle collision
• Non-traumatic CCF seen in elderly, female more common than male
• Clinical: venous hypertension (i.e., proptosis, chemosis, retinal hemorrhage, headache)
• Feared complication: venous hypertension of deep vein system and subsequent venous infarction (this can occur if flow from carotid into the cavernous sinus is diverted into deep venous system)

Urgent Treatment Required If:

• Worsening symptoms: increasing proptosis, diminishing visual acuity, increasing intraocular pressure, elevated intracranial pressure
• Extension of pseudoaneurysm or venous varix, or rupture into subarachnoid space

Treatment: endovascular occlusion of fistula with a detachable balloon device, while preserving flow in the carotid artery. Coil embolization is an alternative possible treatment.

Reference:

Morris P. Practical Neuroangiography, 2nd edition, 2007.

Occupational Radiation Dose Limits

Facts:

• International Commission on Radiological Protection (ICRP) issues periodic recommendations on radiation protection. The Commission was founded in 1928.
• ICRP's latest publication was Publication 103 (2007)
• ICRP effective dose limit for radiation worker (occupational dose limit) = 20 mSv per year when averaged over 5 years; any year limit to 50 mSv
• The most highly exposed workers are unlikely to receive regular annual effective doses more than 5 mSv
• Radiation workers should be monitored using personal dosimeter (film badges, TLDs)
• In emergency situations, occupational exposure can exceed these dose limits if lifesaving actions are involved. Older workers with low lifetime accumulated effective doses should volunteer for emergencies.

Reference:

Huda W. Review of Radiologic Physics, 3rd edition, 2009.

Image Credit: www.thermo.com

Extraadrenal Pheochromocytoma: MRI

Fig. 1: Axial T2-weighted MR image with fat suppression shows a well circumscribed retroperitoneal soft tissue mass below the aortic bifurcation with heterogeneous high T2 signal intensity.
Fig. 2: Post contrast MR image shows heterogeneous enhancement of the mass.

Facts: Extraadrenal Pheochromocytoma

• 10% of all pheochromocytoma
• Most in the abdomen (98%)
• Along prevertebral and paravertebral ganglia, including the organ of Zuckerkandl (which is the only macroscopic extraadrenal sympathetic paraganglia located at the origin of inferior mesenteric artery)
• Benign or malignant difficult to determine by histology. If there is local invasion or metastasis to non-chromaffin tissues --> malignant
• Extraadrenal pheochromocytoma metastasizes more often than adrenal counterpart

MR Imaging Appearance

• High T2 signal intensity, classic "salt-and-pepper" pattern on T2WI
• Enhancing, usually heterogeneous
• No lipid content (lack of signal dropout on opposed-phase images)

Our case - extraadrenal pheochromocytoma below the aortic bifurcation incidentally found on MRI, confirmed with I-123 MIBG and serum catecholamines. It should be noted that half of all pheochromocytomas are now discovered incidentally on imaging.

Reference:

Elsayes KM, Narra VR, Leyendecker JR, et al. MRI of adrenal and extraadrenal pheochromocytoma. AJR 2005;184:860-867.

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Ultrasound Features of Malignant Breast Mass

An ultrasound image shows an irregular solid mass with malignant features including ill-defined border, microlobulations, spiculations (seen as hyperechoic band around the mass), taller than wide and angular margin. This was confirmed to be invasive ductal carcinoma at biopsy.

US Features of Malignant Breast Mass

• Marked hypoechogenicity
• Spiculation: highest positive predictive value for malignancy
• Taller than wide
• Angular margin
• Shadowing
• Microlobulation
• Duct extension
• Calcifications
• Branch pattern

Reference:

Cardenosa G. Breast imaging companion, 2nd edition, 2000.

Microcolon with Features of Low Intestinal Obstruction

Barium enema in a 2-day old boy shows diffuse small caliber of the colon (arrows). Retained barium is noted in the stomach from a recent upper GI study (which was normal). Note the presence of air in the rest of the small bowel (tubular lucent areas in the background) indicating that this is a low intestinal obstruction.

Differential Diagnosis: Microcolon with Features of Low Intestinal Obstruction

• Pathology of colon itself: colonic atresia, diffuse Hirschsprung's disease
• Pathology of distal small bowel (no bowel content can pass into colon resulting in small colon caliber): ileal atresia, meconium ileus

Approach: when seen evidence of bowel obstruction in a neonate, one needs to distinguish between high and low intestinal obstruction. High obstruction presents with little amount of gas in the bowel, dilated stomach and/or duodenum. If high obstruction due to midgut volvulus is suspected, upper GI study is the next step. If low obstruction is suspected, barium enema is performed. In this case, we see a lot of bowel gas in the neonate with clinical intestinal obstruction and a barium enema shows diffuse microcolon - the differential diagnoses are either diseases of distal small bowel or of the colon itself.

Our case: distal ileal volvulus with possible meconium ileus producing distal intestinal obstruction and microcolon

Reference:

Davies SG. Chapman & Nakielny's Aids to Radiological Differential Diagnosis, 5th edition, 2009.

Calcified Lung Masses

Fig. 1: Chest radiograph of a 24-year-old man shows a dense retrocardiac opacity and a dense nodule in the right lower lobe (arrows).
Fig. 2: Axial CT image confirms the presence of multiple nodules in the lungs (arrows). The nodules/masses have a soft tissue component and are partially calcified. They are predominantly in the lower lung zones.

Differential Diagnosis:

• Calcified/ossified metastasis: osteosarcoma, chondrosarcoma, mucinous adenocarcinoma of colon or breast, papillary carcinoma of thyroid, cystadenocarcinoma of ovary and carcinoid
• Infections: tuberculosis, histoplasmosis
• Treated neoplasm: lymphoma following radiotherapy

Our case: calcified/ossified metastases from osteosarcoma

Reference:

Davies SG. Chapman & Nakielny's Aids to Radiological Differential Diagnosis, 5th edition, 2009.

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Occipital Condylar Fracture

Axial and coronal-reformatted CT images show a bone fragment inferomedial to the left occipital condyle, representing type III occipital condyle fracture. There is asymmetric widening of the left lateral atlantodental interval as well. Subsequent MRI (not shown) reveals disruption of the alar and transverse ligaments.

Facts:

• Occipital condylar fracture was likely underdiagnosed before the use of MDCT in craniocervical trauma
• Patients usually (but not necessarily) have severe head, brain and neck trauma from high-speed deceleration insults
• Incidence ranges from 3-16% of all high-speed head & neck trauma
• Complex mechanism, usually with a combination of flexion/extension, lateral bending and axial rotation of the craniocervical junction

Classification

• Most widely used one is "Anderson and Montesano"
• Type I = comminuted fracture with minimal or no displacement
• Type II = basilar skull fracture extending to the occipital condyle
• Type III = fracture with a fragment displaced medially from the inferomedial aspect into the foramen magnum (as in our case)

Note: This fracture can be easily overlooked even on MDCT. You need to think about it and look for it.

Reference:

Leone A, Cerase A, Colosimo C, et al. Occipital condylar fracture: a review. Radiology 2000;216:635-644. Free Full Text

Temporomandibular Osteoarthritis

Coronal and sagittal CT images of the temporomandibular (TM) joints show narrowing of the joint spaces, rough articular surface, erosions and subchondral sclerosis. Abnormal contour of the condyles and eminences are due to severe degenerative disease.

Facts:

• Degenerative joint disease is the most common disease of the TM joint
• On histopathological study, it is found in 40% of cases over 40 years of age
• Changes in the articular surface originates in posterior aspect then spreads to larger areas, cartilage loss results in destruction of condyle, bony eburnation, flattening and joint space narrowing
• Often associated with internal derangements related to meniscal dysfunction (dislocation with or without reduction)

Imaging

• On radiograph, CT and MRI, there is "roughening" of condylar surface, flattening of condyle and eminence, osteophytes, eburnation (cartilage replaced by bone at the site of erosion) and narrowing of joint spaces
• CT arthrography or MRI are likely the optimal imaging means to evaluation status of meniscus

Reference:

Katzberg RW, Keith DA, Guralnick WC, et al. Internal derangement and arthritis of the temporomandibular joint. Radiology 1983;146:107-112.

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CT Slice Thickness

Single Detector Array Scanners

• Determined by physical collimation of the x-ray beam (green structure in the picture)
• As this gap widens, the slice thickness increases
• Upper limit of slice thickness depends on the width of the detector

Multiple Detector Array Scanners

• Determined by width of the detectors (between blue lines in the picture)
• Width of the detectors can be changed by 'binning' different numbers of individual detector elements together
• Can be used in conventional axial scanning (no table movement) and in helical scanning protocols

Tradeoffs Respect to Slice Thickness

• Number of detected x-ray photons increases linearly with slice thickness, for scans performed at the same kV and mAs
• As number of detected x-ray photons increases, the signal-to-noise ratio (SNR) increases.
• Higher SNR means better contrast resolution
• Example: going from a 1-mm to 3-mm slice thickness triples the number of detected photons, and the SNR increases by square root of 3 = 73%
• Increased slice thickness will reduce spatial resolution and increase volume averaging in the thickness dimension

References:

Bushberg, et al. Essential Physics of Medical Imaging, 2nd ed, 2001

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