Pelvic neurofibroma arising from prostate in a case of neurofibromatosis-1.

Pelvic neurofibroma is a rare condition and can be associated with neurofibromatosis-1 (NF-1). The diagnosis is primarily based on histopathology, though certain characteristic imaging features like the 'target sign' on T2W MRI are highly suggestive of the diagnosis. We describe a case of pelvic plexiform neurofibroma in a case of NF-1.

INTRODUCTION

Pelvic neurofibroma is a rare entity and around 60 cases have been reported so far.[1] Prostatic neurofibroma is even rare. Urinary bladder is the most commonly involved organ in pelvic neurofibroma; which can be an isolated finding or as a part of neurofibromatosis-1 (NF-1). The clinical presentation is often with irritative and obstructive voiding symptoms. We present a case of NF-1 with pelvic neurofibroma.

CASE REPORT

A 12-year-old male child was presented to the Department of Pediatrics with symptoms of insidious onset of urinary obstruction and fullness in the lower abdomen. He had no history of burning micturition, urgency or recurrent urinary tract infection. On examination he had axillary freckling and multiple cafe-au-lait spots in his lower back. Neurological examination was unremarkable and he had no family history of NF-1. A pelvic ultrasound revealed hypoechoic irregular mass lesion involving the base of the bladder. Pelvic MRI was performed to characterize the lesion. T2-weighted (T2W) MR image of the pelvis revealed a large heterogeneously hyperintense mass lesion involving the base of bladder, the prostate and extending cranially into the rectovesical pouch [Figures 1 and 2]. The lesion was hypointense on T1W images. Caudally the lesion reached below the pelvic diaphragm and it displaced the urinary bladder anteriorly. Some part of the lesion showed “target appearance” characteristic of anerve sheath tumor [Figure 1]. After Gadolinium administration, the lesion did not show any significant enhancement on immediate post-contrast images [Figure 3a] but had significant retention of contrast on 20-minute-delayed images [Figure 3b]. The lesion was extending till the ureterovesical junction (UVJ) but there was no hydroureteronephrosis. There is associated dural ectasia involving the lower lumbar and sacral region [Figure 1]. An image-guided biopsy of the pelvic mass lesion was performed which revealed loosely arranged spindle-shaped neural cells with myxoid stroma. A diagnosis of pelvic plexiform neurofibroma was made and taken up for surgical resection of the mass. Intraoperatively, the mass was diffuse and infiltrated the prostate, bladder base and perivesical space though it was resectable. The rectum and the UVJ were free. Post-operative procedure was uneventful and there was remission of symptoms.

Figure 1

Sagittal T2W MRI showing heterogeneous hyperintense mass lesion involving the bladder base and prostate, protruding into the perineum and displacing the urinary bladder anterosuperiorly. There is associated dural ectasia (block arrow). The hypointense central fibrous structure giving rise to the ‘target sign’ is shown with an arrow

Figure 2

Axial T2W fat-saturated image of the pelvis reveals the mass to be heterogeneously hyperintense with target sign (arrow)

Figure 3

(a) Axial T1W fat-saturated MRI immediately after administration of Gadolinium reveals minimal peripheral contrast enhancement of the mass. (b) Axialdelayed contrast-enhanced fat-suppressed T1W image shows intense enhancement of the mass

DISCUSSION

Neurofibromatosis is an autosomal dominant phakomatosis first described by Von Recklinghausen in 1882. There are several diagnostic criteria which include one plexiform or multiple neurofibroma, iris Lisch nodules, axillary freckling, multiple cafe’-au-lait spots, characteristic bony changes, optic nerve glioma, family history of NF- 1, etc. Most common site of visceral involvement in NF is the gastrointestinal tract. When it involves the genitourinary tract (which by itself is are), the urinary bladder is the most commonly involved organ.[23] Pelvic neurofibroma can occur either as an isolated pathology or in a case of NF-1. Tumors arise from the nerve plexus near the bladder trigone and can involve the prostate, seminal vesicle, urethra in males and urethra, vagina or urethra in females.[2] A large tumor can surround the rectum or protrude in the perineum, as in this case. Common presenting clinical features include frequency, recurrent urinary tract infection or urgency. Malignant degenerations, though rare, are known to occur. In a case of neurofibroma with other stigma of the syndrome, the diagnosis of a pelvic neurofibroma is easier; but in isolated cases the differential of a bladder base mass in a young adult should include rhabdomyosarcoma, paraganglioma, ganglioneuroma and rarely leiomyosarcoma. Imaging modalities include computed tomography (CT) and MRI. On CT, the lesions are hypodense and show heterogenous enhancement, but often they lack any characteristic feature for definitive diagnosis. On MRI, they are usually of heterogenous hyperintense signal on T2W images and low intensity on T1W images. The “target sign” on T2W MRI representing central low-intensity fibrosis surrounded by hyperintense myxoid stroma is highly suggestive of neurofibromas.[45] The stroma enhances after contrast administration. Both CT and MRI can show nodular bladder wall thickening and extension into the paravesical space and lateral pelvic wall.[6] Masses which extend to the neural foramina are highly characteristic for neurogenic tumors. MRI is the investigation of choice. Few recent studies have also reported the efficacy of newer technique like MR volumetry in inoperable cases of plexiform neurofibroma in NF.[7] The final diagnosis can be based on the histopathological findings.