| Abstract|| |
Inflammatory myofibroblastic tumors (IMTs) are uncommon benign neoplasms in the abdomen, and urachal involvement is very rare. IMT of the urachus is usually mistaken clinically and radiologically for a malignant tumor. The tumor has spindle cell proliferation with a prominent inflammatory infiltrate and myxoid degeneration favoring other designations such as inflammatory pseudotumor and fibromyxoid pseudotumor. Complete excision is the treatment of choice. The case documented here was in a 50-year-old male, with an abdominal mass diagnosed on computed tomography scan as adenocarcinoma of urachus infiltrating the bladder. Histopathology showed a benign spindle cell tumor invading bladder muscle. Immunohistochemistry aided in diagnosing an anaplastic lymphoma kinase (ALK)-1 positive IMT. Approximately, 50% of the IMTs show ALK positivity, and though when present, it indicates neoplastic nature of the spindle cells, the pathogenesis of IMT is still elusive. The urachal IMTs need documentation in literature for their rarity and diagnostic dilemma posed by them.
Keywords: Anaplastic lymphoma kinase-1 positivity, inflammatory myofibroblastic tumor, urachus
|How to cite this article:|
Venkatesh K, Madhusudhan H R. Anaplastic lymphoma kinase positive inflammatory myofibroblastic tumor of the urachus: A rare neoplasm in an unusual location. Indian J Pathol Microbiol 2016;59:93-5
|How to cite this URL:|
Venkatesh K, Madhusudhan H R. Anaplastic lymphoma kinase positive inflammatory myofibroblastic tumor of the urachus: A rare neoplasm in an unusual location. Indian J Pathol Microbiol [serial online] 2016 [cited 2020 Sep 19];59:93-5. Available from: http://www.ijpmonline.org/text.asp?2016/59/1/93/178240
| Introduction|| |
Inflammatory myofibroblastic tumors (IMTs) also called as inflammatory pseudotumors are rare benign lesions causing diagnostic dilemma for clinicians, radiologists, and pathologists. The tumor was first described by Roth in 1980, in the bladder of a 32-year-old female presenting with a history of recurrent cystitis.  Urachus is a vestigial structure rarely involved by neoplasms and most of them are malignant. The urachal IMT may show anaplastic lymphoma kinase (ALK) rearrangement by immunohistochemistry and fluorescence in situ hybridization techniques.  The case reported here is an IMT of the urachus which is extremely rare in adults.
| Case report|| |
A 50-year-old male presented with dysuria and intermittent gross hematuria of 15 days duration. Urine culture was negative, and cytology showed red blood cells and pus cells. Ultrasonography showed a urinary bladder mass/hematoma with small calcific specks. Other findings included prostatomegaly, cystitis, and bilateral small renal stones. The patient underwent transurethral prostatectomy along with lithotripsy and a bladder biopsy was taken. Histopathology showed cystitis and benign prostatic hyperplasia. There was no tumor seen in the bladder biopsy. The patient was asymptomatic for about 5 months after which he presented with pain abdomen. The computed tomography (CT) scan was done which showed an enhancing nodular lesion measuring 3.8 cm × 2.8 cm at the anterosuperior margin of the urinary bladder having both intravesicular component and cord like extention up to the umbilicus. The intravesicular component had irregular margins without abdominal or peritoneal infiltration. Liver, gallbladder, kidneys, and spleen were normal. CT scan report was that of an urachal neoplasm suggestive of adenocarcinoma with bladder infiltration (Stage IIIA) [Figure 1]a and b]. The patient underwent partial cystectomy with complete resection of the tumor.
|Figure 1: (a and b) Computed tomography scan pictures showing a nodular enhancing lesion in the anterosuperior margin of the urinary bladder reported as adenocarcinoma arising from urachus with an extension into the dome of the bladder. (c) Gross specimen of chord like urachus (arrow) with nodular mass extending into the bladder wall. (d) Cut surface showing gray white and gelatinous tumor extending into the upper portion of bladder|
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Grossly, the soft tissue mass had an elliptical piece of skin over it and cord like urachus measuring 6.0 cm × 2.5 cm. Attached to this was partial cystectomy specimen measuring 5.0 cm × 5.0 cm and with a thin layer of peritoneal fat. Cut section showed nodular glistening, gray-white, and soft to firm mass in lower part of the urachus measuring 3.8 cm × 3.0 cm extending into the bladder wall [Figure 1]c and d]. The bladder mucosa showed yellowish and hemorrhagic areas.
Microscopically, the skin was unremarkable. Sections from the nodular mass showed spindle cells having eosinophilic cytoplasmic processes arranged in interlacing bundles. The cells exhibited moderate nuclear pleomorphism with occasional large nuclei and mitosis. Myxoid and edematous areas were seen with foci of necrosis. There was prominent lymphoplasmacytic infiltrate, at places forming lymphoid follicles. Fibrosclerotic areas with hyalinized thick walled blood vessels were noted. The neoplastic tissue was seen insinuating between muscle bundles of the bladder and there was chronic cystitis with foci of granulation tissue [Figure 2].
|Figure 2: (a) Microscopy showing neoplasm composed of spindle cells in bundles admixed with chronic inflammatory cells (H and E, ×10). (b) Prominent lymphoplasmacytic infiltration amidst spindle cells (H and E, ×40). (c) Fibromyxoid and a focal necrotic area. (d) Urachal tumor next to the bladder wall. (e) Bladder muscle invasion and a lymphoid follicle seen. (f) Bladder mucosa showing chronic inflammation (H and E, ×10)|
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Immunohistochemistry showed strong cytoplasmic positivity of tumor cells for ALK-1 [Figure 3]a and b and smooth muscle actin [Figure 3]c and negative for DOG1 (to rule out gastrointestinal stromal tumor) and CD34 [Figure 3]d and e.
|Figure 3: (a) Immunohistochemistry showing tumor cells exhibiting anaplastic lymphoma kinase - 1 cytoplasmic positivity (IHC for anaplastic lymphoma kinase - 1, ×10). (b) Anaplastic lymphoma kinase - 1 positivity under higher magnification (×40). (c) Tumor cells positive for smooth muscle actin just like the adjacent bladder muscle bundles. (d) Tumor cells negative for DOG1. (e) Negative for CD34 unlike the vascular lining (×10)|
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The patient is symptom free with no recurrence after 3 years of follow-up.
| Discussion|| |
The urachus is a vestigial remnant derived from urogenital sinus (precursor of the urinary bladder) and allantois (part of yolksac). The urachus gets obliterated and seen as a fibrous band between the umbilicus and the dome of urinary bladder. The urachal disorders include sinus or cyst formation, infections, and calculus formation or calcification. Tumors are rare, 95% are epithelial, and the remainder is mesenchymal tumors. About 90% of all urachal malignancies are adenocarcinomas, and interestingly urothelial and squamous cell carcinomas are rare. The first case of adenocarcinoma of urachus was described in a 32-year-old female by Roth. The urachal malignancies comprise only 0.34% of bladder neoplasms.  Benign tumors of the urachus are extremely rare and include fibromas, fibroadenomas, fibromyomas, leiomyomas, and hamartomas. Clinically patients present with hematuria, abdominal mass, and rarely with umbilical discharge. The extensive literature search yielded only five cases of urachal IMTs and all in children and none in adults. ,,,, Interestingly, the case presented here was in an adult.
The preoperative diagnosis of a tumor of urachal origin is important as the surgical management is different from that for primary neoplasms of the bladder. Urachal neoplasms in supravesical location, without extention into the bladder wall are easily diagnosed. Dilemma arises, when the neoplasm is intramuscular or intramucosal, to determine whether it is a primary bladder neoplasm or urachal. Six diagnostic criteria to support the urachal origin of malignancies have been described by Wheeler and Mustofi.  They are: (1) tumor located in dome of anterior wall of bladder, (2) bulk of tumor located in muscularis than in lamina propria, (3) tumor infiltration of the bladder wall with contiguous spread to the anterior abdominal wall, (4) urachal remnant associated with tumor, (5) a sharp demarcation between the tumor and the overlying bladder mucosa, and (6) absence of glandular or polypoid proliferations of bladder mucosa.
IMT of the bladder is more frequent in males and male to female ratio is approximately 3:1, and the age ranges between 7 and 77 years.  The differential diagnoses include postoperative spindle cell nodule, leiomyoma, neurofibroma, leiomyosarcoma, sarcomatoid carcinoma in adults, and embryonal/botryoid rhabdomyosarcoma in children. Classical histology with spindle cells having minimal atypia and inflammatory cell component aided by cytoplasmic positivity for ALK-1 will support the diagnosis of IMT. 
IMT though first described in the lungs, has been reported in different parts of the body. A study including 59 cases of IMTs revealed that abdomen-pelvic location was the most common (64%) followed by lungs (22%), head and neck (8%), and extremities (5%). Abdominal-pelvic IMTs had a recurrence rate of 85%. Recurrent and metastatic IMTs were larger, ALK-negative, found in older patients and had greater nuclear pleomorphism with atypical mitoses.  IMT as suggested by its name was previously considered as a reactive condition. The ultrastructural studies suggest that the spindle cells are of fibroblastic or myofibroblastic origin. ALK-1 has emerged as a fairly specific marker for IMT, but not very sensitive. ALK is a tyrosine kinase receptor, a member of the insulin growth factor superfamily and expressed by neoplastic fibroblasts. Although the ALK-1 positivity supports neoplastic nature of IMT, still the pathogenesis remains elusive. Immunohistochemistry shows negative results with CD34, myoglobin, DOG1, and S100.
| Conclusion|| |
Although benign tumors of urachus are very rare, the possibility of IMT should be considered. Immunostaining for ALK positivity aids in diagnosis and is a favorable prognostic indicator as emphasized by the nonrecurrence of the tumor in this case.
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3]