Pituitary adenomas need to be differentiated from other saddle, suprasaddle and parasaddle disorders. In adults, most saddle lesions are pituitary adenomas, while in children, most saddle lesions are craniopharyngiomas and germ cell tumors, and pituitary adenomas are rare. Specific diseases include the following.
1. tumors or pseudotumors.
(1) Pituitary carcinoma or pituitary carcinosarcoma: fast growth rate, the differentiation from pituitary adenoma needs to rely on pathological diagnosis, and its pathological cell nuclear division phase is mostly seen.
(2) Pituitary tumors.
(1) Metastases: they are the most common tumors of the posterior pituitary gland or the entire pituitary gland, probably related to the abundant blood supply, with breast and lung being the most common primary foci.
(ii) Pituitary cell tumor: the most common tumor originating from the pituitary gland/pituitary stalk (primary).
(3) Astrocytoma: originates from the pituitary stalk or the posterior pituitary gland.
(3) Pituitary hyperplasia: Hypothyroidism can cause thyrotropin cell hyperplasia, which in turn leads to chronic stimulation of the pituitary gland by TRH, usually resulting in normal or reduced free T4 and markedly elevated TSH, with symmetrical masses in the saddle area on MRI images. In addition, the pituitary gland is usually slightly enlarged in women of childbearing age.
(4) Craniopharyngioma; it accounts for 20% of tumors in adults and 54% in children.
(5) Rathke’s Cleft Cyst: a non-neoplastic lesion, a remnant of Rathke’s bursa, often appears as a low-density cystic lesion on CT, and its MRI presentation varies.
(6) Meningioma (pars plana, saddle node and septum): The difference between meningioma of saddle node and pituitary macroadenoma on MRI is as follows: (1) there is obvious and homogeneous enhancement after contrast-enhanced scan (while pituitary macroadenoma enhancement is not obvious and homogeneous); (2) the center of the tumor is located in the suprasaddle (vs. intersaddle); (3) the dural base is tapered and expanded (dural tail sign). Meanwhile, the pterygoid saddle is usually not enlarged, and even larger suprasellar meningiomas rarely present with endocrine dysfunction. Meningioma may squeeze the pituitary stalk to displace it posteriorly, which may be accompanied by dilated pneumatization of the pterygoid sinus (enlargement of the pterygoid sinus beneath the tumor but no destruction of bone).
(7) Tumors of germ cell origin: choriocarcinoma, germ cell tumor, teratoma, embryonal carcinoma, and endodermal sinus tumor. Suprasellar germ cell-derived tumors are more common in women, and in men, they are common in the pineal region. Suprasellar germ cell tumors can present with uveitis, visual field defects, the triad of total hypopituitarism, and also with obstructive hydrocephalus. Lesions occurring in both the suprasellar and pineal regions can be diagnosed as germ cell tumors.
(8) Glioma: including hypothalamic glioma and optic nerve (or optic cross) glioma.
(9) Metastases: may be combined with clinical manifestations of the primary lesion.
(10) Chordoma.
(11) Parasitic infections: such as cysticercosis.
(12) Epidermoid cysts.
(13) Suprasellar arachnoid cyst.
(14) Sarcoidosis: involvement of the hypothalamus may cause anterior and/or posterior pituitary dysfunction =
(15) Bone abnormalities: giant cell tumor of bone, chondroblastoma, brown tumor of bone in patients with hyperparathyroidism, bone redundancy formation, extramedullary hematopoiesis.
2. Vascular diseases.
Aneurysm: It can occur in anterior communicating artery, internal carotid artery (cavernous sinus or superior pituitary artery) as well as ophthalmic artery and basilar artery bifurcation. Giant aneurysms may produce an occupying effect. MRA/CTA may be performed to confirm or exclude the diagnosis in cases of suspected saddle aneurysm.
Carotid cavernous sinus leak (CCF): the typical triad of “bulbar conjunctival edema, pulsating proptosis, and ocular murmur” may be present.
3. Inflammatory diseases.
Autoimmune pituitary inflammation: Clinically, there is often uveitis (pituitary adenomas rarely present with uveitis), and imaging shows enlarged pituitary gland, thickened pituitary stalk, inconspicuous enhancement, small lesions at first visit, loss of high signal in posterior pituitary lobe, and no change in saddle base. There are two forms of presentation.
(1) Lymphatic (adenosquamous) pituitaryitis: the more common form. Inflammation of the pituitary stalk leads to lymphocytic infiltration. The etiology is related to an autoimmune reaction, but the specific antigen remains to be determined. Most cases occur in women in late pregnancy and early postpartum.
(2) Granulomatous pituitaryitis: more aggressive, gender-neutral, and not associated with pregnancy. The etiology may be autoimmune, but the exact pathogenesis is unknown.
It is sometimes difficult to distinguish between autoimmune pituitary inflammation and non-functioning pituitary macroadenoma (enhanced in the saddle, normal endocrine examination), and it may be more reasonable to use medical therapy, such as hormonal use or interruption of possible causative factors.
Pituitary abscesses: can develop from inflammation of the pterygoid sinus/paranasal sinus or other sites, or from infection resulting from previous surgery for saddle lesions; in some patients, no clear source of primary infection can be found. Clinically, it mostly presents with total pituitary hypoplasia and uveitis, and can present with visual field impairment and oculomotor dysfunction due to oculomotor nerve palsy. On imaging, it presents as a cystic occupancy in the saddle area, with circumferential enhancement around the lesion on enhanced scan. In terms of treatment, anti-infection, hormone and neurotrophic drugs are given first. In some patients, the lesion shrinks or even disappears after the above treatment, while those whose lesions do not shrink or increase in size need surgery. In some patients, it is difficult to distinguish the lesion from pituitary adenoma cystic lesion before surgery, and the abscess is confirmed to be pituitary abscess only during surgery. The contents of the abscess are not cultured for pathogenic bacteria.
4.Empty saddle syndrome.
It can be primary empty saddle syndrome, and secondary empty saddle syndrome can appear after surgery of saddle area lesion.