Indian Journal of Cancer Medknow Publications on behalf of Indian Cancer Society ISSN: 0019-509X EISSN: 1998-4774 Vol. 39, Num. 4, 2002, pp. 151-153

Indian Journal of Cancer, Vol. 39, No. 4, (October - December 2002) , pp. 151-153

Neurofibromatosis : A Diasnostic Mimicker on CT in a known case of Malignancy

Rajiv Verma, A. Chhabra, C. Bhutani, Deepak Jain, Jaswinder Singh

Department. of Radiology, Rajiv Gandhi Cancer Institute, New Delhi.

Code Number: cn02014

ABSTRACT

A known case of early carcinoma cervix was found to have mediastinal widening on chest radiograph and hypoechoic oval retroperitoneal lesions on USG abdomen. CECT chest and abdomen showed these to be non enhancing lymphnode like round to oval discrete mass lesions in mediastinum, abdomen and pelvis. With no other suggestion of carcinoma spread, local or distant and uncommon incidence of extensive lymphadenopathy in a early carcinoma cervix, biopsy from one of the representative lesion was performed which revealed it to be benign neurofibroma. Differentiation of these strategically located benign nerve sheath tumors from lymphadenopathy can sometimes be challenging on CT scan and in a known case of malignancy or with history of surgery for malignant neoplasm it may cause concern for disease spread or local tumor recurrence. Associated imaging and clinical features can sometimes be helpful in reaching the correct diagnosis.

Key Words: Neurofibromatosis, Neurofibroma, Lymphadenopathy, CT.

INTRODUCTION

Neurofibromas may manifests as solitary tumors or may be one of the manifestations of neurofibromatosis. Neurofibromatosis typeI(NFI), formerly known as Von­recklinghausen's disease is one of the most common autosomal dominant disorder, occurring in approximately one in 4000 births. It has a variety of localized or more frequently, systemic manifestations throughout the thorax, abdomen, pelvis and extremities. NF1 with abdominopelvic involvement tends to arise in the retroperitoneal, mesenteric and paraspinal regions, it maybe quite extensive and therefore difficult to distinguish from lymphadenopathy at CT. Familiarity with the various manifestations of NF1 in different anatomic locations is important in making the diagnosis and optimizing post diagnostic treatment. In patients with known unrelated malignancy or otherwise it can prove to be a challenge in differentiating it from lymphnode which is indicative of the disease spread.

CASE REPORT

A 40-years-old woman presented with occasional intermenstrual bleeding. Pelvic examination, PAP smear and punch biopsy revealed a localized stage lb carcinoma cervix of squamous cell differentiation. On initial metastatic work up, chest radiograph and USG abdomen revealed superior mediastinal widening and retroperitoneal and lower abdominal hypoechoic oval lesions, respectively. Suspecting it to be lymphadenopathy, CT chest and abdomen were carried out which showed multiple round to oval hypodense nonenhancing soft tissue attenuation mass lesions in paratracheal, prevascular, azygoesophageal recess, paraoesophageal, peripancreatic, superior mesenteric, paraaortic, aortocaval and pelvic, regions suggestive of extensive lymphadenopathy. Lesions were discrete with no evidence of calcification, necrosis or confluence. Since it is not usual to find extensive nodal spread in a localized carcinoma cervix, a suspicion of associated additional pathology was raised and patient underwent CT guided FNAC sampling, which was proven to be negative for the malignancy. Trucut biopsy from one of the suspected pelvic node reported it to be a benign neurofibroma. Retrospective examination of patient revealed multiple cutaneous macules on the back & shoulder and a small neurofibroma on the left calf. There was no family history of neurofibromatosis.

DISCUSSION

Neurofibromas are benign neural tumors, consisting of fibroblasts, Schwann cells and neural elements that expand and diffusely infiltrate the nerve. Variable degrees of myxoid degeneration may be seen.¹ Neurofibroma may manifest as solitary tumors or may be a manifestation of neurofibromatosis. Neurofibromatosis typeI is the most common of the phakomatosis, inherited as autosomal dominant disorder, however up to 50% of cases occurs sporadically due to spontaneous mutation. Most of the affected patients present in childhood with classic clinical findings. Up to 10% of patients present later in life with atypical manifestations. The typical clinical picture of NF1 consists of multiple spots of hyperpigmentation (cafe au lait spot) and cutaneous and subcutaneous tumors. Additional diagnostic criteria include axillary freckling, iris hamartomas and bone dysplasia, affected first degree relations and multiple CNS tumors such as optic nerve glioma.² However, occasionally Neurofibromas are found during surgical intervention or incidentally at radiological imaging, as occurred in our case. These patients usually display mild cutaneous symptoms.

The CT findings in patients with peripheral nerve sheath tumors have been well described and depend largely on the histological characteristics of the tumors. On contrast enhanced CT, these tumors demonstrate characteristic low attenuation in 73% of cases³ however; some may show soft tissue attenuation. Factors responsible for this low attenuation include cystic degeneration, xanthomatous features, confluent areas of hypocellularity and lipid laden - schwann cells. In plexiform tumors, low attenuation may result from trapped perineuronal adipose tissue. Occasionally a peripheral region of contrast enhancement may occur due to more peripheral cellular and fibrous elements whereas central myxomatous and cystic regions are comparatively hypovascular.

In thorax neurofibromas occurs along the course of vagus, phrenic, recurrent laryngeal or intercostal nerves and on CT appear typically as well marginated, smooth, round or elliptic masses. Variable degree of contrast enhancement and calcification may be seen. Both common & plexiform neurofibromas may closely mimic localized or extensive lymphadenopathy and can result in diffuse mediastinal widening as seen in numerous other conditions like lymphoma, sarcoid, tuberculosis etc. Sometimes they may also insinuate themselves into adjacent mediastinal structures such as esophagus and simulate primary disease. In paravertebral locations, these may mimic extramedullary hematopoesis, ganglioneuroma or neurenteric cysts. When they demonstrate very low attenuation (10-20HU), differentiation from congenital mediastinal cystic lesions may be difficult.

In abdomen, neurofibroma tend to arise in the retroperitoneal, mesenteric and paraspinal regions. Focal involvement of individual organs is rare but does occur and on CT scan, may again closely mimic lymphadenopathy. Often, these masses may have low attenuation & mimic other causes of low attenuation lymphadenopathy like whipple's disease, tuberculosis, metastases from seminoma, etc.

Neurofibromas located in iliac and obturator chains, also closely mimic lymphadenopathy. In pelvis and in patients with history of malignant neoplasm main cause of concern for local tumor occurrence is differentiation from lymphadenopathy. It may be aided by presence of other associated features like limb hemihypertrophy with associated degenerative arthritis. Sacral lesions due to remodeling caused by dural ectasia or by simple enlargement of neural foramina. However in our case no such finding was present.

Other peripheral manifestations that can aid in diagnosis include pseudoarthrosis, peripheral nerve neurofibromas and subcutaneous common & plexiform neurofibromas. Peripheral nerve tumor may become quite large and may resemble primary soft tissue sarcoma.

MRI can be of great valve in diagnosing extensive neurogenic tumors. Multiple ring like structures are seen within the masses on T2W images, representing nerve tissue and areas of myxoid degeneration. Peripheral nerve tumors typically have low to intermediate signal intension on T 1 W and heterogeneous at T2W with high signal - intensity regions corresponding to areas of myxoid or cystic degeneration.⁴ Nodular areas of low signal intensity corresponds to collagen and fibrous tissue, which may enhance after administration of gadolinium based contrast giving typical target appearance.

Neurofibromatosis can give rise to various misleading appearances on CT scan and is especially troublesome in cases with known malignancy or history of surgery for malignant neoplasm where it may cause concern for disease spread or local tumor recurrence. In a case appearing as generalized lymphadenopathy on CT scan, a high level of suspicion with associated cutaneous & skeletal manifestations can help clinching the correct diagnosis and avoid unnecessary biopsy. MR imaging is helpful in distinguishing neurofibromas in confusing cases given the characteristic contrast enhancement pattern and imaging finding seen with T2W sequences due to the presence of central collagen fibres.⁵

Due to variable presentations of this disease and apparent lack of supportive features in some cases, it may sometimes become necessary to go for biopsy especially when correct diagnosis can alter the prognosis and course of treatment.

REFERENCES

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2. Williams M, Verity C.M. Optic nerve gliomas in children with neurofibromatosis. Lancet 1987;1:1318-9.
3. Ross CR, McCauley DI, Naidich DP. Intrathoracic neurofibroma of the vagus nerve associated with bronchial obstruction. J Compet Assist Tomogr 1982;6:406-12.
4. Matsuki K, Kakitsubata Y, Watanabe K, Tsukino H, Nakajima K. Mesentric plexiform neurofibroma associated with Recklinghausen's disease. Pediatr Radiol 1997;27:255-6.
5. Bhargava R, Parham DM, Lasater OE, Chari RS, Chen G, Fletcher BD. MR imaging differentiation of benign and malignant peripheral nerve sheath tumors: use of the targer sign. Pediatr Radiol 1997;27:124-9s.

Copyright 2002 - Indian Journal of Cancer.