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Imaging of a rare disorder: Macrodystrophia lipomatosa.

Introduction

Macrodystrophia lipomatosa (MDL) is described as a rare, non-hereditary, congenital condition presenting with localised macrodactyly and a proliferation of mesenchymal elements. There is in particular a marked increase in fibroadipose tissue. (1)

We describe 2 young patients presenting to our department in a 6-month period, with a history of disproportionately large limbs since birth. While our first case demonstrated all the typical features of MDL, our second case failed to demonstrate osseous gigantism, but all other features of MDL were present. An extensive search of the literature failed to yield any cases described without osseus gigantism; but at the same time, the other radiological features failed to fit in with any other causes of focal gigantism, and the most appropriate diagnosis appears to be MDL. We therefore concluded that this may be a case of a rare, atypical MDL that was arrested or frustrated and so failed to demonstrate full expression of the syndrome.

Case 1

A 33-month-old boy was referred by a paediatric surgeon for radiographs of the left arm. According to the history, he was born with the left arm disproportionately larger than the rest of the body. Clinically, there was marked increase in the soft-tissue bulk of the entire left arm with focal gigantism involving the thumb and second finger. Good functionality of the arm was maintained.

Radiographs revealed lucent soft-tissue thickening of the affected arm, suggesting the presence of fat (Fig. 1). Focal gigantism involving the metacarpals and phalanges of the thumb and second finger were noted. The rest of the bony elements were normal.

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Ultrasound (US) examination demonstrated an extensive increase in subcutaneous tissue with poor visualisation of muscles and nerves. Normal vascularity was noted on Doppler US. US of the abdomen was normal.

MRI studies showed diffuse proliferation of fatty tissue throughout the arm, with fat infiltration of the muscles (Figs 2-4). The nerves could not be identified on MRI, probably owing to infiltration by fat. Histological analysis of the tissue revealed adipose tissue only, which was in keeping with a diagnosis of MDL.

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Case 2

An 11-month-old girl was referred by a plastic surgeon for MRI to exclude lymphoedema of the right lower limb. According to the history, she was born with the right lower limb disproportionately bigger than the rest of the body. Clinically, there was marked increase in soft tissue of the entire right lower limb. Good function of the limb was maintained, and the child was otherwise normal.

Radiographs revealed increased soft tissue throughout the limb, and the underlying bones were normal (Fig. 5). US was not performed. MRI showed diffuse increase of fat in the soft tissues, as well as scattered cystic lesions of varying signal intensity (Figs 6-8). This feature has not been described in the literature reports of other cases of MDL, and was thought to be due to either fat necrosis or old haematomas secondary to trauma. There was no fat infiltration of the muscles, and the neurovascular bundles were intact.

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Once again, histological analysis revealed proliferation of adipose tissue in keeping with a diagnosis of MDL.

Literature review

MDL is a rare congenital disorder of focal gigantism affecting the extremities--more commonly, the second and third digits of the foot, but it may also affect the hand. (2), (3) It is characterised by the proliferation of all mesenchymal elements but especially of fibroadipose tissue. (2), (4), (5) It is typically described in a particular nerve distribution; usually the medial plantar nerve or median nerve. (3)

Radiological investigations include plain film radiographs, US and MRI, where findings may be typical. Plain films show lucent soft-tissue overgrowth as well as hypertrophy of osseous structures in the distribution of the median and plantar nerves. (1) In our cases, only one patient demonstrated the osseous overgrowth. In the second case, the bony elements were within normal limits. In older patients, secondary osteoarthritis changes may also be seen.

US reveals large amounts of subcutaneous tissue, infiltration of the muscle and thickening of the affected nerves. Doppler studies reveal an absence of any increased vascularity.

MRI findings are most useful in confining the differential diagnosis. (4) MRI investigations reveal overgrowth of unencapsulated fatty tissue that demonstrates high signal on T1WI and T2WI, with suppression of the signal on short inversion time inversion recovery (STIR) sequences, as demonstrated by our patients. Thickened nerves may, or may not, be demonstrated.

Lack of flow voids and calcifications helps to differentiate the condition from vascular malformations of Klippel-Trenauney-Weber syndrome. Lymphangiomas and neurofibromas may be hyperintense to fat on T2WI, (4) distinguishing MDL from these conditions. Proteus syndrome may be similar but has other associated features such as skull anomalies, lung cysts and pigmented naevi. (1) Some authors suggest that MDL is a localised form of Proteus syndrome. (1) Fibrolipomatous harmatoma of the nerve displays features similar to MDL; (1) however, fat deposition is within the nerve, giving a speckled appearance on MRI.

Two subtypes of the condition are described in the literature: the static and progressive types. In the static type, the enlarged digits grow at the same rate as the other digits. In the more rare progressive type, the growth of the enlarged digits is more rapid. Our patients were thought to have the static type clinically.

Conclusion

Numerous aetiologies of focal gigantism exist. While clinically the distinction may be difficult, radiological investigation is very useful in confining the differential diagnosis. MRI in particular shows characteristic findings of MDL, and radiologists therefore play an important role in the diagnosis of these conditions.

(1.) Sone M, Ehara S, Tamakwa Y, Nishida J, Honjoh S. Macrodystrophia lipomatosa: CT and MR findings. Radiat Med 2000; 18(2): 129-132.

(2.) Singla V, Virmani V, Singh P, Khandelwal N. Case report: Macrodystrophia lipomatosa--illustration of two cases. Indian J Radiol Imaging 2008; 18(4): 298-301.

(3.) Turkington JRA, Grey AC. MR imaging of macrodystrophia lipomatosa. Ulster Med J 2005; 74(1): 47-50.

(4.) Blacksin M, Barnes FJ, Lyons MM. MR diagnosis of macrodystrophia lipomatosa. Am J Radiol 1992; 158: 1295-1297.

(5.) Balakrishna BV, Prasad SRH. Macrodystrophia lipomatosa--A rare congenital disorder. Indian J Radiol Imaging 2005; 15: 349-352.w

Farhana Ebrahim Suleman, MB ChB, FCRad (D) SA, MMed Rad (D)

Department of Radiology, University of Limpopo, Medunsa Campus, Garankuwa

Margaret Kisansa, MB ChB, MMed Rad (D)

Department of Radiology, George Mukhari Hospital, Garankuwa
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Author:Suleman, Farhana Ebrahim; Kisansa, Margaret
Publication:South African Journal of Radiology
Article Type:Case study
Geographic Code:6SOUT
Date:Jun 1, 2010
Words:1076
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