Secondary Chondrosarcoma from Osteochondroma in proximal humerus.

Radiograph of humerus 3 years before the present MRI showing sessile osteochondroma (arrow)

The present radiograph showing development of secondary chondrosarcoma.

The present CT scan axial section of the proximal humerus showing large exophytic mass with calcification seen in the posterior aspect. The mass is continuous with the cortex of the humerus (arrows).

T1 weighted image showing mixed signal intensity of the mass with multiple areas of calcification.

STIR coronal image showing the large mass predominantly hyperintense signals.

Axial T2 image showing the cortical continuity with the mass lesion.

Discussion:

Malignant Transformation of solitary osteochondroma <1% and for multiple exostosis is ~13%.

The cartilaginous cap deserves the most attention when differentiating a benign osteochondroma from a secondary chondrosarcoma that arose from a pre-existing osteochondroma.

In adults, the cartilaginous cap regresses and becomes thin due to enchondral ossification of the majority of the cap.

Malignant transformation is suggested by: 

• Cartilaginous cap thickness greater than 2cm 
• Cortical destruction 
• Back growth of the cartilaginous cap into the stalk or medullary canal
• Lysis of calcifications in cap

Imaging:

Radiograph:

• Chondroid Calcification in cap
• Increasing destruction or change in appearance is worrisome for malignancy

Ultrasound - Good for cap and bursae

Bone Scan - Increased uptake in the cap

MRI: Best test for evaluating thickness of cap and surrounding bursa

• Intermediate T1W Images
• High Intensity T2W Images because of fluid content

CT:

• The cap will appear as soft tissue with calcification
• Can be difficult to distinguish from muscle

Cap thickness:

• Benign < 1.5cm (0.1 - 3.0cm; Avg. 0.6 - 0.9 cm).
• Malignant > 1.5 cm (1.5 - 12cm; Ave. 6cm).

Hot cross bun sign - Multiple system atrophy

Transverse and sagittal T2-weighted MRimage of the brain of a patient with multiple system atrophy (MSA) of the cerebellar-predominant subtype (MSA-c) shows the hot cross bun sign as a cruciform hyperintensity

in an atrophied pons. Cerebellum and middle cerebellar peduncles are also atrophied.

Discussion:

Multiple system atrophy is a rare neurological disorder characterized by a combination of parkinsonism, cerebellar and pyramidal signs, and autonomic dysfunction. The term "Multiple System Atrophy" is synonymous with striatonigral degeneration (SND) when Parkinsonism predominates, olivopontocerebellar atrophy (OPCA) when cerebellar signs predominate, and Shy-Drager syndrome when autonomic failure is dominant. The incidence (new case per 100,000 person years) for ages 50 to 99 years is 3.0 (Bower et al, 1997), or about half as frequent as it's close relative, progressive supranuclear palsy (PSP). The mean age of onset is 54.

Pathophysiology: There is neuronal loss and gliosis in the inferior olives, pons, cerebellum, substantia nigra, locus ceruleus, striatum and the intermediolateral column of the spinal cord.

Similar pattern of neuronal loss is seen in a patient with parkinsonism, the neuronal loss being secondary to presumed vasculitis, and proposed that the sign may reflect wallerian degeneration of transverse pontocerebellar fibers secondary to vasculitic infarction.\

MRI - On T2-weighted MR images, a hyperintense rim at the putaminal edge, putaminal atrophy, and intrinsic signal intensity change are seen. In MSA-c, the changes predominantly affect the infratentorial structures. On T2-weighted MR images, atrophy and increased signal intensity within the pons, cerebellum, and middle cerebellar peduncles are seen.

References

1. Schrag A, Kingsley D, Phatouros C, et al. Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry 1998;65:65–71.

2. Muqit MM, Mort D, Miskiel KA, Shakir RA. “Hot cross bun” sign in a patient with parkinsonism secondary to presumed vasculitis. J Neurol Neurosurg Psychiatry 2001;71:565–566.

Achilles tendon rupture - MRI

The STIR and T1 weighted sagittal images of the lower leg and ankle of a 52 year old female presented with trauma showing ruptured Achilles tendon (arrow) with proximal retraction of the tendon evidenced by wavy pattern of the hypointense tendon (arrow heads).

Achilles tendon tears may be grouped into 4 types ( according to severity of the tear and degree of retraction).

• type I : partial ruptures <= 50%
  • typically treated with conservative management
• type II : complete rupture with tendinous gap <= 3 cm
  • typically treated with end-end anastomosis
• type III : complete rupture with tendinous gap 3 to 6 cm
  • often requires tendon / synthetic graft
• type IV : complete rupture with defect of > 6 cm (neglected ruptures)
  • often requires tendon / synthetic graft and gastrocnemius recession.
  Reference: MAFFULLI NICOLA. “Current Concepts Review - Rupture of the Achilles Tendon.” J Bone Joint Surg Am 81, no. 7 (July 1, 1999): 1019-36.

Aberrant right subclavian artery

Coronal curved CT reformatted image of the 62 year old male patient presented with cough showing incidentally detected aberrant right subclavian artery arising from the left sided aortic arch (arrow).

Axial curved CT reformatted image of the 62 year old male patient presented with cough showing incidentally detected aberrant right subclavian artery arising from the left sided aortic arch (arrow) causing compression on the esophagus.

Sagittal oblique curved reformatted image better depicts the aberrant artery.

Discussion:

The aberrant artery usually arises just distal to the left subclavian artery and crosses in the posterior part of the mediastinum usually behind the esophagus on its way to the right upper extremity. Such course of this aberrant vessel may cause a vascular ring around the trachea and esophaugus. Dysphagia due to an aberrant right subclavian artery is termed dysphagia lusoria. Palsy of the recurrent laryngeal nerve is termed Ortner's syndrome.

The aberrant right subclavian artery frequently arises from a dilated segment of the proximal descending aorta, the so-called Diverticulum of Kommerell.