Clinical Profile:

A 32-year-old man came with complaints of chronic diarrhoea and melena since four months.

Radiological findings:

The radiograph of the  pelvis is shown below (Fig. 1)

 Fig1 : The radiograph of the pelvis  shows irregular destruction of the left transverse process of L5 and the adjacent ala of the sacrum

Ultrasonogram shows a well-defined, lobulated. heterogeneously hyperechoic lesion. There is no significant vascularity on color Doppler (Fig 2).

Fig 2 Ultrasonogram shows a well-defined lobulated heterogeneously hyperechoic lesion. There is no significant vascularity on color Doppler.

Plain, arterial and delayed phase axial CT scans of the abdomen show a well-defined, heterogeneously enhancing, fat containing retroperitoneal mass in the presacral region with no calcifications. There is sclerosis of the sacral bone posterior to it. There is mass effect on the mid rectum which is displaced anteriorly. There is no invasion of adjacent structures (Fig. 3)

Fig 3

The MRI shows the following findings (Fig. 4)

Fig. 4 MRI shows heterogenous lesion with T2 hyperintense areas within. On T1 fat sat the lesion is hyperintense with few hypointense areas within. The lesion does not show diffusion restriction.

Radiological diagnosis:  

Benign presacral tumor

Pathological diagnosis:

 A CT guided core biopsy of the lesion was performed.

Core biopsy on hematoxylin and eosin staining shows scattered hematopoietic cells admixed with mature fat cells

Fig. 5 Core biopsy on hematoxylin and eosin staining shows scattered hematopoietic cells admixed with mature fat cells

Final diagnosis: 

Presacral myelolipoma

Treatment:

 The patient will be managed conservatively.

 Timeline:     

Discussion

Myelolipoma is a rare, well-capsulated, benign tumour that contains mature adipose tissue and various combinations of trilineage haematopoietic cells (red blood cells, white blood cells and platelets). It manifests in four distinct clinicopathologic patterns: isolated adrenal myelolipoma, adrenal myelolipoma with haemorrhage, extra-adrenal myelolipoma and myelolipoma associated with other adrenal disease. (1)

Although the etiology is unknown, there are several theories on the pathogenesis of this tumour:

• metaplasia of uncommitted adrenal cortical mesenchymal cells;

• migration of haematopoietic tissue to the adrenal gland during intrauterine development.

For extra-adrenal myelolipomas there are two main pathogenetic hypotheses:

• embolization of bone marrow tissue;

• reactivation of peritoneal embryonic connective haematopoiesis tissue, in response to a triggering stimulus, like an endocrine dysfunction or in septic/infectious conditions. (2)

Myelolipoma occurs most commonly in adrenal glands. Extra-adrenal myelolipomas predominate in females (2:1) and in middle-aged to elderly patients (mean age 60 years) and vary in size (from 2 up to 26 cm). The extra-adrenal locations include presacral and perirenal retroperitoneum, mediastinum, liver, stomach, lungs, pelvis, spleen, mesentery and muscle fascia. In some cases, extra-adrenal myelolipomas have been described in association with Cushing syndrome, Addison disease, adrenal hyperplasia and chronic exogenous steroid use.

Presacral region represents 50% of all extra-adrenal locations. The tumours are usually asymptomatic and discovered incidentally but large lesions could become symptomatic due to haemorrhage or mass effect on adjacent structures like ureters, bladder, rectum and sacral nerve roots or plexus with symptoms of urinary retention, constipation or lower extremity radiculopathy. (5) These lesions are typically round or oval masses, well-capsulated and adherent to the sacrum without invasion of bone or sacral nerve roots.

The imaging appearance of myelolipomas varies according to tumour composition. Ultrasonography could show a hyperechoic mass (if fat predominates) or a hypoechoic mass (when there is a predominance of erythroid and myeloid cells). The variable amount of fat affects typical low attenuation CT values of the lesion that usually has some intralesional areas with higher attenuation values due to hematopoietic solid tissue islands, which may enhance after IV injection of iodine-based contrast.(3) On MRI, fatty elements show high signal intensity (SI) on T1w and T2w sequences, which is promptly suppressed on fat-saturation pulse sequences, whereas haematopoietic tissue islands show lower signal intensity on T1w and T2w with variable enhancement after IV administration of paramagnetic contrast. (4)

Conclusion:

Several masses could be found in the presacral region incidentally or otherwise; they may be benign or aggressive. Differentiating presacral myelolipomas from other congenital or acquired presacral masses could be crucial for patient management.

References: 

1. Baker KS, Lee D, Huang M, et al. Presacral myelolipoma: a case report and review of imaging findings. J Radiol Case Rep. 2012;6(6):1–9

2. Saboorian MH, Timmerman TG, Ashfaq R, et al. Fine-needle aspiration of a presacral myelolipoma: a case presentation with flow cytometry and immunohistochemical studies. Diagn Cytopathol. 1999;20(1):47–51.

3. Kumar M, Duerinckx AJ. Bilateral extraadrenal perirenal myelolipomas: an imaging challenge. Am J Roentgenol. 2004;183(3):833–836. 

4. Kammen BF, Elder DE, Fraker DL, et al. Extraadrenal myelolipoma: MR imaging findings. Am J Roentgenol. 1998;171(3):721–723. 

5. Singla AK, Kechejian G, Lopez MJ. Giant presacral myelolipoma. Am Surg Apr. 2003;69:334–338.

Acknowledgement :

We are grateful to the Department of Pathology at our institution for sharing the histopathology image with a legend.