Monday, December 11, 2017

Pleomorphic adenoma

Magnetic resonance imaging (MRI) of parotid pleomorphic adenoma. T1- and T2-weighted and post-contrast sequences

Pleomorphic adenoma (also known as benign mixed tumor) is the most common tumor of the major salivary glands, and the most common benign tumor of the parotid glands (~75% of all benign salivary gland tumors). Prior head and neck irradiation is a risk factor. They are typically solitary, slowly growing, and asymptomatic. They are typically diagnosed after palpation by the patient or incidentally on imaging studies. Surgical resection is advised due to risk of malignant transformation.

On MRI, pleomorphic adenomas, have polylobulated margins a rim of low T2 signal corresponding to a fibrous capsule. They have heterogeneous low-to-intermediate signal intensity on T1-weighted images. High T2 signal and avid, solid enhancement are considered relatively specific features, especially when present in a younger patient (< 57 years). Dynamic contrast-enhanced (DCE) MRI shows gradual enhancement. On diffusion-weighted imaging (DWI), pleomorphic adenomas tend to have very high ADC values; however, DWI is not able to differentiate between benign and malignant parotid gland tumors.

On ultrasound, pleomorphic adenomas are typically hypoechogenic. They can have mild to moderate uptake on FDG PET.

Differential considerations include:
  • Warthin tumor: 10–15% are bilateral. Can have proteinaceous cystic components with high T1 signal ranging from a few millimeters to 1–2 cm. Solid components have rapid enhancement and washout.
  • Adenoid cystic carcinoma: Small, low-grade lesions can be mistaken for pleomorphic adenomas. Variable signal intensity on T2-weighted depending on type. Low-grade tumors have high T2 signal in the solid parts. Large tumors can have cystic areas of hemorrhagic necrosis.
  • Myoepithelial adenoma: Also tend to have very high ADC values
  • Basal cell adenoma: More commonly in the superficial lobe of the parotid gland. Tend to be round and well-circumscribed tumors. Have heterogeneous enhancement on CT.
  • Carcinoma in pre-existing pleomorphic adenoma (carcinoma ex pleomorphic adenoma): Typically less well-circumscribed than benign pleomorphic adenoma. Tends to occur after 10–15 years of an existing pleomorphic adenoma, with sudden rapid growth (3–6 months) in patients in the sixth-to-eighth decades of life.
  • Lymphoma: Tend to be multiple. Can have well-defined and lobulated margins. Tend to have low T2 signal and slight enhancement.
  • Sarcoid: Can be placed in any differential, including this one.

References

Sunday, July 9, 2017

Hemochromatosis: Hand Manifestations


50-year-old man with subtle manifestations of hemochromatosis arthropathy. Note narrowing of the metacarpophalangeal (MCP) joints, more advanced at the index and middle fingers. Other features of hemochromatosis arthropathy are not present, specifically, there is no subchondral cyst formation, hook-like osteophytes, osteoporosis, or chondrocalcinosis and the radiocarpal articulation is unaffected.

Hemochromatosis: General
  • Autosomal recessive disorder
  • Several genes implicated
  • Body has mechanism for dealing with low Fe (increased intestinal absorption), but no effective way of dealing with excess Fe
  • Fe accumulates in organs
  • Damage via Fe2+ -> Fe3+ -> Oxidation -> Free radicals


Arthropathy
  • Present in 50% of patients when rigorous criteria are used to define arthritis
  • Males affected earlier and more severely
  • Associated with use of joint
  • Typically a chronic process
  • Acute episodes of inflammatory arthritis may occur: May be associated with recovery of CPPD crystals from joint fluid aspiration.
  • Rare syndrome of septicemia accompanied by monoarticular or oligoarticular septic arthritis caused by Yersinia species described: Prosthetic joints seem especially susceptible to this infection.


Pathophysiology
  • Hemosiderin found in superficial synovial lining cells and macrophages (phagocytosis of iron loaded synoviocytes)
  • Very little iron detected in deeper synovial layers, and only occasionally in macrophages.
  • Arthropathy generally non-inflammatory. Chronic inflammatory cell infiltrate rarely seen.
  • Minimal to no iron deposition in cartilage.
  • Chondrocalcinosis a frequent finding
  • No close spatial relationship between iron and CPPD crystals, and crystals can be found even in the absence of iron deposits.


Imaging Features
  • Overlap with those of idiopathic OA and CPPD
  • Joint space narrowing
  • Subchondral sclerosis
  • Subchondral cysts
  • Osteophyte formation (hook-like osteophytes can be seen)
  • Chondrocalcinosis in articular and non-articular cartilage
  • Osteoporosis


The deal with chondrocalcinosis
  • Fe2+ (but not Fe3+) inhibits pyrophosphatase
  • Leads to diminished hydrolyzation of inorganic pyrophosphate
  • Contributes to precipitation of inorganic pyrophosphate with calcium.

References

  • Dallos T, Sahinbegovic E, Aigner E, Axmann R, Schöniger-Hekele M, Karonitsch T, Stamm T, Farkas M, Karger T, Cavallaro A, Stölzel U, Keysser G, Datz C, Schett G, Manger B, Zwerina J. Validation of a radiographic scoring system for haemochromatosis arthropathy. Ann Rheum Dis. 2010 Dec;69(12):2145-51.
  • Frenzen K, Schäfer C, Keyßer G. Asymmetrical hemochromatosis arthropathy in a patient with a history of poliomyelitis. Rheumatol Int. 2012 Apr;32(4):1045-7.
  • van Vulpen LF, Roosendaal G, van Asbeck BS, Mastbergen SC, Lafeber FP, Schutgens RE. The detrimental effects of iron on the joint: a comparison between haemochromatosis and haemophilia. J Clin Pathol. 2015 Aug;68(8):592-600.

Sunday, July 2, 2017

Chordoma Drop Metastases



Chordoma drop metastases are extremely rare, with ~11 reported cases. Of these, 1 was present at the time of initial presentation and 3 were only seen at autopsy. The naturally slow growth of chordomas, lack of symptoms in several cases, and late age of onset may mask true incidence of intradural drop metastases.

The imaging features are nonspecific and tend to mirror those of the primary neoplasm.

References

Martin MP, Olson S. Intradural drop metastasis of a clival chordoma. J Clin Neurosci. 2009 Aug;16(8):1105-7.

Monday, June 26, 2017

Radiation-Associated Sarcomas


Patient with history of radiation therapy for head and neck cancer. Radiation field extended into the supraclavicular nodal stations. CT shows an osteoid producing soft tissue mass to the right of midline. Bone scan and PET show uptake in the lesion, as well as contralateral lymph nodes. PET shows an FDG-avid lung nodule. T1-WI post-contrast MRI with FS shows a peripherally enhancing soft tissue mass.

The incidence of radiation-associated sarcomas of bone and soft tissue is about 0.1%. They are more commonly seen in patients with breast cancer, lymphoma, head and neck malignancies, and gynecologic cancers. The distribution of primary cancers is likely related to the larger numbers of patients with these cancers and the high survival rates for these tumors.

The majority of radiation-associated tumors are soft tissue sarcomas, with bone sarcomas making up about 20-30% of cases. The majority are high grade and aggressive. The most common soft tissue sarcomas are unclassified pleomorphic sarcoma (UPS, formerly MFH), followed by angiosarcoma (particularly in breast cancer), fibrosarcoma and leiomyosarcoma (particularly in retinoblastoma). The most common bone sarcomas are osteosarcomas.

The latency between radiation and sarcoma ranges from as little as a few months to 54 years. The average is 7 to 16 years. In breast cancer, the average is 10 to 11 years (4-8 years for angiosarcomas). In childhood cancers, the average latency is between 12 to 13 years.

Risk factors include, dose (Rarely seen with low doses: <40 Gy), age at exposure, concomittant chemo exposure (particularly alkylating agents) and genetic tendency (e.g., Li-Fraumeni syndrome).

References

Maki, R. et al. Radiation-Associated Sarcomas. UpToDate

Sunday, June 18, 2017

Keloids and Hypertrophic Scars


T1 axial post-contrast MRI of a keloid or hypertrophic scar formation along the margins of a myocutaneous flap. The enhancement can fool you into thinking that there is recurrent tumor, but the linear pattern along the flap margin is the clue that this is related to the scar.

Keloids and hypertrophic scars are fibroblastic proliferations of the dermis. Their morphologic and pathologic features overlap. They are associated with trauma, infection, and connective tissue diseases. They do not spontaneously regress and tend to recur after surgical excision, so surgery is often combined with topical corticosteroid injection or, less commonly, radiation therapy.

In contrast to hypertrophic scars, keloids tend to grow beyond the margins of the injury site, have keloid collagen, and are less likely to stain for smooth muscle actin. Keloids have a higher recurrence rate than hypertrophic scars.

Keloids are hypocellular and are composed of dense collagen. The abundance of type I collagen results in low T2 signal. Keloids occur most frequently in patients aged 15–45 years. People of African and Chinese origin have a higher predilection for keloids. The face, shoulders, forearms, and hands are most commonly affected. They tend to occur where there is increased skin tension

References

Dinauer PA, Brixey CJ, Moncur JT, Fanburg-Smith JC, Murphey MD. Pathologic and MR imaging features of benign fibrous soft-tissue tumors in adults. Radiographics. 2007 Jan-Feb;27(1):173-87.

Monday, June 12, 2017

The axillary nerve and adhesive capsulitis


The axillary nerve (yellow arrow) and the posterior humeral circumflex artery (red arrow) in the region of the quadrilateral space. Note proximity to the inferior capsule.

The axillary nerve is closely related to the inferior capsule of the shoulder. It passes inferior to the subscapularis muscle and travels adjacent to the capsule before entering the quadrilateral space.

The axillary nerve is associated with adhesive capsulitis in at least 2 ways.

First, the axillary nerve can be irritated in the setting of inflammation and thickening of the inferior capsule. The evidence for this is somewhat anecdotal, but makes anatomic sense. The image below is from a patient with adhesive capsulitis. Note the teres minor atrophy (green arrow) in the setting of thickening of the inferior capsule (blue arrow), and constrained fluid in the joint (orange arrow) being forced into the superior subscapularis recess (orange*). The bone lesions are from myeloma, in case you were wondering.



Second, the close proximity of the nerve to the joint capsule predisposes it to injury during arthroscopic capsule release for treatment of adhesive capsulitis. Risk of injury is decreased by placing the incision of the glenohumeral joint capsule at the glenoid insertion with the arm in the abducted and externally rotated position.

References

  • Jerosch J, Filler TJ, Peuker ET. Which joint position puts the axillary nerve at lowest risk when performing arthroscopic capsular release in patients with adhesive capsulitis of the shoulder? Knee Surg Sports Traumatol Arthrosc. 2002 Mar;10(2):126-9.
  • E. B. G. D. Santos, P. M. E. Souza (pdf). Teres minor beyond quadrilateral space syndrome: a pictorial review. ECR 2014 conference.

Tuesday, June 6, 2017

Sacrum

I was reading an article on the role of religion in the secular Turkish state and came across this statement:
It is possible -- such is the argument of Carter Findley in his Turks in World History -- that in doing so it drew on a long Turkish cultural tradition, born in Central Asia and predating conversion to Islam, that figured a sacralisation of the state, which has vested its modern signifier, devlet, with an aura of unusual potency.

You may be wondering what the heck a congenital variant of spinal segmentation has to do with religion. From the always-excellent Online Etymology Dictionary:

Bone at the base of the spine, 1753, from Late Latin os sacrum "sacred bone," from Latin os "bone" + sacrum, neuter of sacer "sacred" (see sacred). Said to be so called because the bone was the part of animals that was offered in sacrifices. Translation of Greek hieron osteon. Greek hieros also can mean "strong," and some sources suggest the Latin is a mistranslation of Galen, who was calling it "the strong bone."