Spinal MRI Sagittal T1 of vertebral column. Image 1 clearly illustrates the classic ‘fish vertebra sign’ (also known as the ‘H Shaped Vertebra’ and ‘Lincoln log vertebra) that is so characteristic of Sickle cell anemia. The normal concavity of the vertebrae becomes exaggerated and appears biconcave because of a squared off depression of the vertebral end-plates with corresponding compression of the intervertebral discs.(1) These changes are a result of ischemia, a lack of adequate oxygen supply, caused by microvascular or small blood vessel infarctions (an infarct is a small localized area of dead tissue resulting from failure of blood supply) to the end-plates of the vertebra. The fish vertebra sign is clinically observed in around 10% of patients with sickle cell anemia (2)
Sickle cell anemia, also known as Sickle Cell Disease (SCD), is a hereditary disorder of the blood characterized by the formation of abnormal hemoglobin molecules in the red blood cells. Hemoglobin is a protein carried by red blood cells that is responsible for transporting oxygen around the body. Due to the atypical haemoglobin molecules the red blood cells in Sickle Cell Anemia disease are also abnormal and tend to be more rigid and crescent or sickle shaped. Sickle Cell Anemia is characterized by ischemia and infarction which is caused by the sickle-shaped blood cells obstructing blood vessels and restricting blood flow to organs or other tissues of the body. Another main symptom of Sickle Cell disease is Hemolytic anemia which is a deficiency of red blood cells due to overly rapid breakdown of the red sickle cells. Organs most frequently damaged by Sickle Cell Disease are the spleen, bone marrow, liver and kidneys.(3) Lung disease can also pose a serious problems and a complication of this is pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs) which can lead to heart failure.
The hemolytic anemic state that characterizes Sickle Cell Disease can often cause red bone marrow to be found in abnormal places in the body. Sickle cell patients, through a complicated process, retain the majority of their marrow and this is known as marrow hyperplasia. Marrow hyperplasia leads to thinning of the bone trabeculae which in turn leads to bone weakness and osteoporosis.
Skull X-Ray demonstrating a classic example of ‘hair-on-end’ sign attributed to marrow hyperplasia in a known Sickle Cell Anemia patient. Clearly evident is the expanded medullary, or central, cavity. The diploic space is markedly widened due to marrow hyperplasia. (The Diploic space is the marrow containing area at the vault of the skull between the inner and outer layers of bone). Trabeculae can be seen to be standing upright interspersed with radiolucent marrow hyperplasia to give this classic radiological sign.
1. Williams H J, Davies A M, Chapman S. Bone within a bone. Clin Radiol 2004. 59132–144.144 [PubMed]
2. Ntagiopoulos PG, Moutzouris DA, Manetas S.
3. Bull Eur Physiopathol Respir. 1983 Jul-Aug;19(4):361-6. ‘One view of the pathogenesis of sickle cell diseases’.Charache S.
BMJ Case Rep. 2009;2009. pii: bcr09.2008.0900. doi: 10.1136/bcr.09.2008.0900. Epub 2009 Feb 2. PMID: 21686573 [PubMed]
4.Blood. 2012 Apr 19;119(16):3808-14. doi: 10.1182/blood-2011-08-371062. Epub 2012 Feb 10.’Evidence for both innate and acquired mechanisms of protection from Plasmodium falciparum in children with sickle cell trait.’Gong L1, Maiteki-Sebuguzi C, Rosenthal PJ, Hubbard AE, Drakeley CJ, Dorsey G, Greenhouse B.
5. ‘Protective effects of the sickle cell gene against malaria morbidity and mortality’ The Lancet, Volume 359, Issue 9314, Pages 1311 – 1312, 13 April 2002