Adenomatoid tumor

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sara Mohsin, M.D.[2]

Synonyms and keywords: Benign mesothelioma

Adenomatoid tumor is a rare benign mesothelial tumor affecting female and male genital tract (testicular adnexa). It generally presents in the genital tract, in regions such as the testis and epididymis. However, it also has been found in the pancreas.

• Adenomatoid tumors are benign, solid extratesticular lesions that can originate from the epididymis, tunica vaginalis, or spermatic cord.^[1][2][3]
• They are the most common tumor of the epididymis.^[4][5]
• They occur more often in the lower pole than in the upper pole by a ratio of 4:1.^[6][7][8]
• Usually an incidental finding, adenomatoid tumors manifest as a painless scrotal mass, with the majority diagnosed in patients aged 20–50 years.^[9][10][11]
• They are typically unilateral and occur more frequently on the left side. When they grow noninvasively into the testicular parenchyma, they can simulate intratesticular disease.^{[12][13][14][15]}

• 1 - 5 cm, well circumscribed solid tumor, adherent to testis / testicular adnexa
• Cut surface may have small cystic spaces

• No distinct growth pattern
• Unencapsulated, cuboidal to flat cells forming cords that are either epithelial-like or form channels with dilated lumina simulating vessels
• Cells have acidophilic cytoplasm with cytoplasmic vacuoles
• Nuclei lack nucleoli
• Mitoses and necrosis are usually absent
• Intervening stroma may have smooth muscle and elastic fibers, desmoplastic quality and inflammatory cells
• Rarely, tumor may extend into testicular parenchyma or even rarer, be totally inside the testis^[5][13]
• Patterns have been described but most tumors show a mixture of:^{[16][17][18][19][20]}
  • Adenomatoid (tubular): glandular pattern with cytoplasmic vacuoles giving a signet ring appearance
  • Angiomatoid (canalicular): cells have a more endothelial appearance
  • Solid (plexiform): cells have a more epithelial appearance
  • Cystic (mixed): rare; tumor is in form of cystic spaces lined by cuboidal to flattened lining epithelium

• Smears are moderately cellular with sheets of monotonous round to oval cells showing indistinct cell borders and moderate to abundant pale cytoplasm with vacuolations ^[8][21]
• Nuclei are eccentric in location but regular with inconspicuous nucleoli^[22][3][15]

• Adenomatoid tumor stains positive for:^[10]
  • Calretinin
  • Pan cytokeratins (EMA, AE1 / AE3, Cam5.2)
  • CK5 / 6
  • CK7 (variable, focal to diffuse)
• Adenomatoid tumor stains negative for:
  • Vascular / endothelial markers (CD31, CD34)
  • CEA
  • HBME1
  • Factor VIII Ag
  • MOC31 / BerEP4
  • B72.3
  • CD15
  • Ulex europeus agglutinin I
  • Germ cell markers including:
    • OCT3 / 4
    • SOX2
    • AFP
    • PLAP
    • CD117
    • CD30
    • NANOG

• Prominent microvilli
• Desmosomes
• Tonofilaments associated with dilated intercellular spaces

• Mesothelial origin based on immunohistochemical features and ultrastructural studies ^[23]
• Similar tumor in spermatic cord, ejaculatory duct, fallopian tube, uterus

• 30% of testicular adnexal tumors, 73% of benign tumors of testicular adnexa in study of 314 tumors^[24]
• Most commonly affects individuals in third to fifth decade of life with mean age of invlovement being 36 years
• Rarely can affect the two extremes of age:
  • A case report of adenomatoid tumor in a 5 year old boy^[25]
  • A case report of adenomatoid tumor in a 70 year old man^[26]
• White race is more prone to develop adenomatoid tumor
• Males are more likely to develop adenomatoid tumor comparative to females

• Schimmelpenning syndrome is associated with the presence of multiple adenomatoid odontogenic tumors^[27]
• Wilms tumors 1 WT1 gene has been implicated in the formation of the adenomatoid tumors^[28]
• Chronic myeloid leukemia (CML) patients on imatinib therapy may present with adenomatoid tumor as an incidental finding

• Uniformly benign behavior, no reports of malignant transformation

• Diagnosis is suspected clinicoradiologically, confirmed histologically

• Sites involved by adenomatoid tumor are mentioned in the table below:

Presents as:

• An incidental finding (asymptomatic for several years)
• A solid, well circumscribed, slowly growing scrotal mass
• Painless enlargement (normal scrotal skin and surrounding adenexa)
• Pain (often)
• Small in size usually ranging from 0.5–5.0 cm (rarely larger exceeding 2 cmm3)^[71]
• Benign (even if it extends into testis)

• No specific laboratory finding; however, negative markers for germ cell tumor are helpful in excluding a germ cell malignancy

• On an ultrasound, they appear as a solid, homogeneous, extratesticular mass with variable echogenicity (hyperechoic or hypoechoic).^[72]
• USG reveals a relatively hypo, iso to hyperechoic mass at lower pole of epididymis, not distorting the testis

• Commonly, MRI demonstrates low signal intensity relative to the testicular parenchyma on T2-weighted images.
• MRI can aid in determining the paratesticular origin of the lesion.
• Adenomatoid tumors enhance after administration of gadolinium contrast material.

• Complete excision
  • Radical orchidectomy
  • Laparoscopic excision of uterine adenomatoid tumor ^[51][50]
• Frozen section examination may prevent unnecessary radical orchiectomy^[73][74]
• Paratesticular tumors are rare tumors that are difficult to diagnose preoperatively and therefore, many patients are subjected to inguinal orchiectomy. However, radical orchiectomy can be avoided as the diagnosis of paratesticular tumor can be made on the basis of clinical suspicion, findings of tumor markers and radiological tests.

• Adenomatoid tumor must be differentiated from:
  • Malignant mesothelioma (HBME1+, mitoses and necrosis)
  • Metastatic adenocarcinoma (positive for one or more of CEA, PSA, MOC31 / BerEP4 and CD15 are useful)
  • Papillary cystadenoma of epididymis

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