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AJR 2005; 184:S94-S96
© American Roentgen Ray Society

Case Report

CT Findings of Pelvic Lipomatosis of Nerve

Drew A. Torigian and Evan S. Siegelman

Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104-0033.

Received February 17, 2004; accepted after revision June 1, 2004.

 
Address correspondence to D. A. Torigian (Drew.Torigian{at}uphs.upenn.edu).


Introduction
Top
 Introduction
Case Report
 Discussion
 References
 
Lipomatosis of nerve, also known as fibrolipomatous hamartoma or fibrofatty proliferation of nerve, is a rare benign tumorlike lesion that most often affects the median nerve or its branches. Rarely, involvement of the nerves of the upper and lower extremities and of the face have been reported [1-7]. Frequently, no symptoms or signs are present, although over 50% of patients are symptomatic because of mass sensation, focal compressive neuropathy, or associated macrodactyly [1, 2, 7-9]. We report the CT findings of a woman with presumed asymptomatic pelvic lipomatosis of nerve involving the right sciatic nerve and lumbosacral plexus, as this lesion may potentially be mistaken for the more common retroperitoneal well-differentiated liposarcoma.


Case Report
Top
 Introduction
 Case Report
Discussion
 References
 
A 64-year-old woman with a surgical history of hysterectomy presented with a feculent brown vaginal discharge. No lower extremity neurologic or musculoskeletal symptoms or signs were present on clinical evaluation, and routine laboratory tests were within normal limits. A contrast-enhanced abdominopelvic CT examination showed a 1.5 x 3.0 cm sigmoid colon carcinoma (Fig. 1A) and vaginal gas consistent with a colovaginal fistula (Figs. 1B and 1C). A 2.5 x 6.5 cm well-circumscribed fusiform mass was present within the right pelvic retroperitoneal space that had attenuation values (range, -30 to -60 H) slightly greater than but similar to those of the adjacent normal retroperitoneal fat. This mass was situated anterior to the right piriformis muscle superiorly and more inferiorly extended along the distributions of the right lumbosacral plexus and sciatic nerve. The anterior branch of the mass extended inferiorly into the pelvis medial to the right obturator internus muscle, whereas the posterior branch of the mass extended through the right greater sciatic foramen into the proximal intermuscular gluteal region. The lesion resulted in anterior displacement of the right external iliac vessels and medial displacement of the right internal iliac vessels. Several serpentine intralesional softtissue attenuation structures that had a spaghettilike appearance in longitudinal section and a coaxial-cable-like appearance in cross-section were considered pathognomonic of lipomatosis of nerve (Figs. 1A, 1B and 1C). No deformity or destruction of the adjacent osseous structures was present.



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  		Fig. 1A. —64-year-old woman with symptomatic colovaginal fistula related to sigmoid colon adenocarcinoma with incidental right retroperitoneal pelvic lipomatosis of nerve. Axial contrast-enhanced CT images through pelvis show spiculated mass of sigmoid colon carcinoma (long thick white arrow) and air in vagina (a) due to colovaginal fistula. Incidental fusiform right pelvic retroperitoneal fatty mass (white arrowheads) with attenuation slightly greater than surrounding normal-appearing retroperitoneal fat follows expected course of right lumbosacral plexus anteriorly and right sciatic nerve posteriorly. Serpentine soft-tissue attenuation structures are within mass (long thin white arrows) with spaghetti-like appearance in longitudinal section and coaxial-cable-like appearance in cross-section, pathognomonic of lipomatosis of nerve.

 


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  		Fig. 1B. —64-year-old woman with symptomatic colovaginal fistula related to sigmoid colon adenocarcinoma with incidental right retroperitoneal pelvic lipomatosis of nerve. Axial contrast-enhanced CT images through pelvis show spiculated mass of sigmoid colon carcinoma (long thick white arrow) and air in vagina (a) due to colovaginal fistula. Incidental fusiform right pelvic retroperitoneal fatty mass (white arrowheads) with attenuation slightly greater than surrounding normal-appearing retroperitoneal fat follows expected course of right lumbosacral plexus anteriorly and right sciatic nerve posteriorly. Serpentine soft-tissue attenuation structures are within mass (long thin white arrows) with spaghetti-like appearance in longitudinal section and coaxial-cable-like appearance in cross-section, pathognomonic of lipomatosis of nerve.

 


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  		Fig. 1C. —64-year-old woman with symptomatic colovaginal fistula related to sigmoid colon adenocarcinoma with incidental right retroperitoneal pelvic lipomatosis of nerve. Axial contrast-enhanced CT images through pelvis show spiculated mass of sigmoid colon carcinoma (long thick white arrow) and air in vagina (a) due to colovaginal fistula. Incidental fusiform right pelvic retroperitoneal fatty mass (white arrowheads) with attenuation slightly greater than surrounding normal-appearing retroperitoneal fat follows expected course of right lumbosacral plexus anteriorly and right sciatic nerve posteriorly. Serpentine soft-tissue attenuation structures are within mass (long thin white arrows) with spaghetti-like appearance in longitudinal section and coaxial-cable-like appearance in cross-section, pathognomonic of lipomatosis of nerve.

 

The patient's sigmoid colon cancer and fistula were treated with surgery, radiation, and chemotherapy. The lipomatosis of nerve was not sampled at the time of sigmoid resection. A follow-up contrast-enhanced abdominopelvic CT performed 3 years later showed no change in the size or appearance of this lesion (Fig. 1D), further supporting a benign cause. In the interim, the patient did not develop lower extremity neurologic and musculoskeletal signs or symptoms.



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  		Fig. 1D. —64-year-old woman with symptomatic colovaginal fistula related to sigmoid colon adenocarcinoma with incidental right retroperitoneal pelvic lipomatosis of nerve. Axial contrast-enhanced CT image through pelvis 3 years later shows no change in right pelvic fatty mass (white arrowheads), consistent with benign cause.

 


Discussion
Top
 Introduction
 Case Report
 Discussion
References
 
The CT imaging findings of lipomatosis of nerve have been described in two reports that both involved the median nerve and included a fusiform mass predominantly of fat attenuation with internal thickened and elongated tubular or serpentine soft-tissue attenuation foci corresponding to nerve fascicles [10, 11]. As described in several reports of lipomatosis of nerve on MRI, this fatty lesion may occasionally have a branched configuration, and the longitudinally oriented cylindrical, linear, or serpentine soft-tissue foci representing neural elements and associated epineural and perineural fibrosis typically have a coaxialcable-like appearance in cross-section and a spaghetti-like appearance in longitudinal section [5-8, 10, 12] Similar morphologic findings on CT are seen in the present case with the exception of location within the pelvic retroperitoneum as opposed to the extremity.

On CT, differential diagnostic considerations of pelvic lipomatosis of nerve include retroperitoneal intraneural lipoma and retroperitoneal well-differentiated liposarcoma. Intraneural lipomas are focal encapsulated tumors located within the nerve sheath that do not involve individual nerve bundles and appear as focal round or oval lesions of homogeneous or nearly homogeneous fat attenuation with crowding of adjacent normal nerve bundles, whereas lipomatosis of nerve tends to involve nerves diffusely [1, 8, 12]. Well-differentiated liposarcoma is the most common subtype of retroperitoneal liposarcoma, with a peak incidence in the sixth and seventh decades of life, whereas lipomatosis of nerve rarely involves the retroperitoneum and tends to affect patients before the fourth decade of life [1, 2, 9, 13]. Furthermore, although well-differentiated liposarcomas are typically seen to contain areas of macroscopic fat (sometimes with streaky, septal, nodular, and/or globular zones of fibrous or sclerotic soft-tissue density), longitudinally oriented cylindrical, linear, or serpentine soft-tissue structures with a coaxial-cable-like appearance in cross-section and a spaghetti-like appearance in longitudinal section are not found in well-differentiated liposarcoma on crosssectional imaging [14-20].

To our knowledge, our case report is the first to show the CT findings of pelvic lipomatosis of nerve with involvement of the sciatic nerve and lumbosacral plexus. The presentation of lipomatosis of nerve in a 64-year-old patient is also unusual. The oldest reported age of presentation of lipomatosis of nerve in the literature is 75 years old, in which a single case of reported involvement of the sciatic nerve was described on MRI [6]. When a fusiform fat-attenuation lesion with longitudinally oriented cylindrical, linear, or serpentine softtissue density structures is revealed with a coaxial-cable-like appearance or a spaghettilike appearance on imaging, this may be considered characteristic for the diagnosis of lipomatosis of nerve and can potentially obviate biopsy or surgery.


References
Top
 Introduction
 Case Report
 Discussion
 References
 

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