Saturday, May 13, 2017

Toxic Osteoblastoma

Toxic osteoblastoma is an extremely rare variant of osteoblastoma that is associated with systemic symptoms, such as fever, anorexia, weight loss. There is also marked systemic periostitis, not only of the involved bone, but also at other skeletal sites.

Patients tend to be young children (5-7 years of age). On physical examination, there is massive swelling, warmth, and induration of the overlying skin and prominent superficial vessels overlying the lesion. Patients can also have hyperdynamic circulation and even high-output cardiac failure. Regional adenopathy can also be present.

The systemic response is thought to be due to an exaggerated immune response to the tumor. Interleukins can lead to fever and the diffuse periostitis, as well as anemia and massive limb swelling and vascular proliferation. Another possibility is toxic substances released by the tumor itself.

The lesions are highly vascular, and arteriovenous shunting within the lesion can lead to finger clubbing and diffuse periostitis and can account for hyperdynamic circulation.

Differential considerations include osteomyelitis and osteosarcoma.

References

Sunday, April 23, 2017

Nerve Root(s)


In season 3, episode 18 of Star Trek: Deep Space Nine Dr. Bashir has to deal with some deep-seated personal issues. One of these is the fact that he graduated second in his medical school class because he mistook a "pre-ganglionic fiber for a post-ganglionic nerve." Spoiler alert: He did it on purpose because he didn't want to deal with the pressure of being first.

Dr. Bashir is not alone. I see this lead to 2 errors every day in our trainees. The clinical implication is zero, because the referring physicians also don't make this distinction (two wrongs do make a right, apparently).

First, take a look at the image below:



Note that there are 2 nerve roots (dorsal and ventral) on each side (left and right). When you say a lumbar disc compresses a nerve root in the central spinal canal, you need to add an "s," because these dorsal and ventral nerve roots travels down together in the cauda equina. Next time you look at an axial T2-WI of the lumbar spine, see if you can see two distinct nerve roots on either side.

Second, note that once we're post-ganglionic, we're dealing with a nerve, not a root. So, if you're talking about a nerve root outside the foramen, you're about as anatomically correct as a Ken doll.


The same goes for the "nerve roots" of the brachial plexus and the famous Randy Travis Drinks Cold Beer mnemonic for the brachial plexus anatomy (sorry, Randy). All is not lost. Just replace Randy Travis with Nikola Tesla.

Reference

  • Basic anatomy that everyone ignores.

Monday, April 10, 2017

False Perpetuations: Main Portal Vein Size and Portal Hypertension

Perpetuation: A main portal vein (MPV) diameter >13 mm is "consistent with portal hypertension" (pHTN)

This cutoff of 13 mm is based on weak literature (mainly from the 1980's), some of which did not include comparison values of normal patients

  • One comparative study using ultrasound found (Radiology 1982; 142: 167-172):
    • In 79 patients with pHTN
      • 36 had a MPV diameter of <13 mm 
      • 33 had a MPV diameter >/= 13 mm
      • The MPV was not visualized in 10 patients
    • In the 45 control patients
      • The MPV diameter was < 13 mm in 41 cases
      • The MPV was not visualized in 4 patients. 

More recent studies have found that there is no significant difference in MPV diameters when comparing patients without cirrhosis to patients with cirrhosis, and the normal MPV diameter is significantly larger than the 13 mm cutoff

  • A study (Eur J Gastroenterol Hepatol 2004; 16:147-155) from King's College using ultrasound (49 controls and 14 cirrhotics) found: 
    • the average MPV diameters were 9.6 cm and 10.8 cm in patients without and with cirrhosis, respectively.
  • A second study (JCAT 2008; 32: 198-203) from UCSF using CT (59 controls and 67 cirrhotics) found:
    • The average MPV diameters were 14.5 cm and 14.8 cm in patients without and with cirrhosis, respectively.
  • Using CT, the MPVs in healthy renal donor patients were measured before and after the administration of intravenous contrast, and in the axial and coronal planes (Abdom Radiol 2016; 41:1931-1936). This study found:
    • The average MPV diameter was 15.5 +/- 1.9 mm
      • This value was significantly different than 13 mm
    • Post-contrast MPVs were 0.56 mm larger compared to non-contrast
    • A positive correlation between BMI and height versus MPV diameter
In fact, the MPV size can be reduced in portal hypertension and has been described as a sign of hepatofugal MPV flow (AJR 2003; 181: 1629-1633). This study found:
  • A MPV diameter of less than 1 cm is a highly sensitive (but not very specific) for MPV flow reversal in patients with cirrhosis

Sunday, March 26, 2017

Ulnar Dimelia

Ulnar dimelia is a rare congenital disorder characterized by duplication of the ulna, absence of the radius, and polydactyly. Patients can also have arterial anomalies, such as absence of the radial artery, duplication of the ulnar artery, and abnormal arterial arches in the hand. Nerve anomalies may also be present and include shortening of the radial nerve and duplication of ulnar nerve (with or without connections to the median nerve)

Radiopaedia has some great images of type I ulnar dimelia

Distinguishing features of the two types of ulnar dimelia
Feature Type I Type II
Index finger 1 2
Lunate 1 2
Trapezoid 1 2

References

  • Afshar A. Ulnar dimelia without duplicated arterial anatomy. J Bone Joint Surg Br. 2010 Feb;92(2):293-6. doi: 10.1302/0301-620X.92B2.23057.
  • Tomaszewski R, Bulandra A. Ulnar dimelia-diagnosis and management of a rare congenital anomaly of the upper limb. J Orthop. 2015 Feb 18;12(Suppl 1):S121-4.

Sunday, March 19, 2017

Chondroblastoma


General

  • Terminology: “giant cell variant” (1927) → epiphyseal chondromatous giant cell tumor → calcifying giant cell tumor → chondroblastoma
  • 1% to 2% of all primary bone tumors
  • 9% of all benign bone tumors
  • Mean age of 15-18 years
  • M >>F
  • Mean duration of symptoms 8.7 months
  • Trivia: Most common benign neoplasm of the patella

Imaging Features

  • Epiphysis/apophysis +/- metaphyseal/diaphyseal involvement
  • Metaphyseal/diaphyseal occurrence without epiphyseal/apophyseal involvement exceptionally rare
  • Proximal tibia >> proximal femur > distal femur > proximal humerus
  • Well-defined, sclerotic margins on radiographs
  • Can involve the cortex, resulting in expansion, thinning, or disruption.
  • Stippled matrix calcification seen in minority of cases
  • Periosteal reaction seen in majority of cases
  • Extensive peri-lesional edema on MRI is common
  • Homogeneously hypointense on T1
  • Variable on T2: can be diffusely hypointense, or have small cystic areas of increased T2 signal or fluid-fluid levels
  • Heterogeneous and moderate enhancement in solid portions. Less commonly, homogeneous and marked enhancement

Differential Diagnosis

Management/Prognosis

  • Curettage or resection
  • RFA (small lesions, small series, not common)
  • Local recurrence rate: 5.0% after curettage
  • Local recurrence rate: 0% after resection
  • Recurrence most frequent in the proximal humerus
  • Malignant transformation and benign pulmonary metastases extremely rare

References

Sunday, March 12, 2017

Fat-containing bone lesions


The presence of fat within a bone lesion is almost always reassuring, although rare exceptions exist. The differential diagnosis includes:
  • Hemangioma:
  • Intra-osseous lipoma and lipoma variants, including fibrolipoma, angiolipoma and myelolipoma.
  • Enchondroma:
  • Liposclerosing myxofibrous tumor (LSMFT): Nearly all occur in the intertrochanteric region. Now felt to represent a variant of fibrous dysplasia.
  • Osteoporosis: Can give the appearance of lucent bone lesions on CT. These won't have defined margins, and measurement of internal attenuation will reveal the fatty nature of the lesion.
  • Bone infarction: Trivial, but included for the sake of completeness
  • Paget disease of bone:
  • Focal red marrow rest: Ill-defined, intermediate T1 signal. May contain subtle areas of internal fat.
  • Lymphoma: Not truly a fat-containing lesion, but can entrap fat as the tumor infiltrates marrow.
  • Sarcoid: The case above shows a patient with sarcoid and nodal, hepatic, and osseous involvement. Can have fuzzy margins ("brush border").
  • Treated metastasis: One of the ways metastases respond to therapy is by developing internal fat. Myeloma lesions can even entirely "disappear" due to fatty replacement.
  • Intra-osseous hibernoma: Rare.
  • Solid variant of aneurysmal bone cyst:
  • Nonossifying fibroma:
  • Erdheim-Chester disease:
  • Malignancy arising from a fat-containing lesion: For example, osteosarcoma arising from bone infarction or Paget.

References

Sunday, March 5, 2017

Subperiosteal hemorrhage in neurofibromatosis type 1



Neurofibromatosis type 1 (NF-1), in addition to a neuroectodermal disorder, is accompanied by mesodermal dysplasia that is accompanied by skeletal changes. The typical osseous findings include bowing of the legs, increase in length of long bones, pseudarthrosis, subperiosteal cyst formation, local bony erosions from adjacent lesions, and intramedullary neurofibromas. Except for the last two, which are due to direct involvement by neurofibromas, the remainder are due to dysplastic changes in bones.

A lesser known osseous presentation in bone is the propensity for subperiosteal hemorrhage and hematoma formation. The cause is unknown, but may be related to:
  • Vascular abnormalities: For example, diffuse flat hemangiomas or plexiform dilated veins, which have been described in patients with hypertrophy of the extremities
  • Dysplastic periosteum: The thinking is that mesodermal dysplasia manifests as an abnormally loose periosteum with poor callus response. This would predispose the patient to the formation and propagation of large subperiosteal hematomas.
  • Direct involvement by neurofibromas: Subperiosteal infiltration by neurofibromatous tissues may loosen the periosteum and allow for massive hemorrhage following minor trauma.

References